Hydrogen and its importance

Hydrogen & itsHydrogen & its
ImportanceImportance
Hydrogen & itsHydrogen & its
ImportanceImportance
Prof. A. BalasubramanianProf. A. Balasubramanian
Centre for Advanced Studies in Earth Science,Centre for Advanced Studies in Earth Science,
University of Mysore, IndiaUniversity of Mysore, India

 Hydrogen is the first element inHydrogen is the first element in
the periodic table.the periodic table.

 Hydrogen is a tasteless, odourlessHydrogen is a tasteless, odourless
and colourless gas.and colourless gas.
 It is one of the most importantIt is one of the most important
chemical elements on earth.chemical elements on earth.
 Hydrogen has the chemicalHydrogen has the chemical
symbol H.symbol H.
 The hydrogen atom is the lightestThe hydrogen atom is the lightest
of all atoms and simplest inof all atoms and simplest in
nature.nature.

 The hydrogen atom is formedThe hydrogen atom is formed
by a nucleus with one unit ofby a nucleus with one unit of
positive charge and onepositive charge and one
electron.electron.
 Its atomic number is 1 andIts atomic number is 1 and
 its atomic weight is 1.008its atomic weight is 1.008
g/mol.g/mol.
HydrogenHydrogen

 The hydrogen molecule consistsThe hydrogen molecule consists
of two hydrogen atoms boundof two hydrogen atoms bound
together, as H2.together, as H2.
 Density is 0.0899*10 -3Density is 0.0899*10 -3
g.cm -3 at 20 °Cg.cm -3 at 20 °C
 Melting point is - 259.2 °CMelting point is - 259.2 °C
 Boiling point is - 252.8 °CBoiling point is - 252.8 °C
HydrogenHydrogen

Part of biogeochemical cyclesPart of biogeochemical cycles
 It recycles as in otherIt recycles as in other
biogeochemical cycles.biogeochemical cycles.
 It is actively involved with theIt is actively involved with the
other cycles like theother cycles like the
 carbon cycle,carbon cycle,
 nitrogen cycle andnitrogen cycle and
 sulfur cycle as well.sulfur cycle as well.

 At room temperature and atmosphericAt room temperature and atmospheric
pressure, pure hydrogen exists as apressure, pure hydrogen exists as a
diatomic gas (H2).diatomic gas (H2).
 There is a small amount of hydrogenThere is a small amount of hydrogen
gas in the Earth's atmosphere; itgas in the Earth's atmosphere; it
makes up less than one part permakes up less than one part per
million.million.
 Because hydrogen gas is so light, mostBecause hydrogen gas is so light, most
of it escaped from the lowerof it escaped from the lower
atmosphere early in the Earth's history.atmosphere early in the Earth's history.
HydrogenHydrogen

 Thirteen and a half percent of theThirteen and a half percent of the
atoms in the Earth's crust areatoms in the Earth's crust are
hydrogen (most of this hydrogenhydrogen (most of this hydrogen
is in sea water), but becauseis in sea water), but because
hydrogen is so light, it makes uphydrogen is so light, it makes up
only 0.75 percent of the Earth'sonly 0.75 percent of the Earth's
crust by weight.crust by weight.
HydrogenHydrogen

 By weight, it is the ninthBy weight, it is the ninth
most abundant element;most abundant element;
 by number of atoms it isby number of atoms it is
the third most abundant,the third most abundant,
after silicon and oxygen.after silicon and oxygen.
HydrogenHydrogen

 Pure, elemental hydrogen must bePure, elemental hydrogen must be
obtained by dissociating hydrogenobtained by dissociating hydrogen
atoms from the compounds thatatoms from the compounds that
contain them,contain them,
 the most plentiful of which arethe most plentiful of which are
water (H2O) and hydrocarbonswater (H2O) and hydrocarbons
such as methane (CH4).such as methane (CH4).

 The name hydrogen wasThe name hydrogen was
derived from two Greekderived from two Greek
words (Gr. hydro,words (Gr. hydro,
water, and genes,water, and genes,
forming) to mean asforming) to mean as
water forming.water forming.
 Hydrogen is a waterHydrogen is a water
forming element.forming element.
 It was named byIt was named by

 Ninety three percentNinety three percent
of all atoms in theof all atoms in the
universe areuniverse are
hydrogen.hydrogen.
 It was firstIt was first
identified by theidentified by the
English scientistEnglish scientist
Henry Cavendish inHenry Cavendish in
1766.1766.

 This element is found in the sunThis element is found in the sun
and also in most of the otherand also in most of the other
stars.stars.
 It plays an important part in theIt plays an important part in the
proton-proton reaction andproton-proton reaction and
carbon-nitrogen cycle, whichcarbon-nitrogen cycle, which
accounts for the radiant energyaccounts for the radiant energy
of the sun and other stars.of the sun and other stars.

 Hydrogen is thoughtHydrogen is thought
to be a majorto be a major
component ofcomponent of
JupiterJupiter

Hydrogen is a majorHydrogen is a major
constituent of the sunconstituent of the sun
 Hydrogen is a majorHydrogen is a major
constituent of the sun andconstituent of the sun and
most stars.most stars.
 The sun burns by a numberThe sun burns by a number
of nuclear processes butof nuclear processes but
mainly through the fusion ofmainly through the fusion of
hydrogen nuclei into heliumhydrogen nuclei into helium
nuclei.nuclei.

Geological information-Geological information-
AbundancesAbundances
 It is very difficult toIt is very difficult to
determine the geologicaldetermine the geological
abundance of hydrogenabundance of hydrogen
with much certainty.with much certainty.
 A general evaluation showsA general evaluation shows
the following figures inthe following figures in
ppb.ppb.

Abundance ppb by weight ppb by atoms
Universe 750,000,000 930,000,000
Sun 750,000,000 930,000,000
Meteorite (carbonaceous) 24,000,000 170,000,000
Crustal rocks 1,500,000 31,000,000
Sea water 107,800,000 662,000,000
Stream 115,000,000 110,000,000
Human 100,000,000 620,000,000
Geological information-AbundancesGeological information-Abundances

IsotopesIsotopes
 The primary isotope of hydrogen,The primary isotope of hydrogen,
H, is known as Protium.H, is known as Protium.
 The other two isotopes areThe other two isotopes are
Deuterium and Tritium.Deuterium and Tritium.
 Hydrogen is the only elementHydrogen is the only element
whose isotopes have been givenwhose isotopes have been given
different names.different names.

 Protium has aProtium has a mass 1, found inmass 1, found in
more than 99.98% of themore than 99.98% of the
natural element;natural element;
 Deuterium has aDeuterium has a mass 2, foundmass 2, found
in nature in 0.015%in nature in 0.015%
approximately, andapproximately, and
 Tritium has aTritium has a mass 3, whichmass 3, which
appears in small quantities inappears in small quantities in
nature, but can be artificiallynature, but can be artificially
produced by various nuclearproduced by various nuclear
reactions.reactions.
Isotopes of HydrogenIsotopes of Hydrogen

Deuterium is a naturallyDeuterium is a naturally
occurring isotope ofoccurring isotope of
HydrogenHydrogen
 Deuterium is used extensively inDeuterium is used extensively in
organic chemistry in order toorganic chemistry in order to
study chemical reactions.study chemical reactions.
 It is also used in vitamin research.It is also used in vitamin research.
 One atom of Deuterium is found inOne atom of Deuterium is found in
about 6000 ordinary hydrogenabout 6000 ordinary hydrogen
atoms.atoms.
 Deuterium is used as a moderatorDeuterium is used as a moderator
to slow down neutrons.to slow down neutrons.

Tritium is anotherTritium is another
isotopeisotope
 Tritium atoms are also present butTritium atoms are also present but
in much smaller proportions.in much smaller proportions.
 Tritium is readily produced inTritium is readily produced in
nuclear reactors and is used in thenuclear reactors and is used in the
production of the hydrogen (fusion)production of the hydrogen (fusion)
bomb.bomb.
 It is also used as a radioactiveIt is also used as a radioactive
agent in making luminous paints.agent in making luminous paints.
 Tritium is a good tracer forTritium is a good tracer for
detecting the movement of fluids.detecting the movement of fluids.

TritiumTritium
 One of hydrogen's isotopes,One of hydrogen's isotopes,
tritium (3H) is radioactive.tritium (3H) is radioactive.
 Tritium is produced in nuclearTritium is produced in nuclear
reactors and is used in thereactors and is used in the
production of the hydrogen bomb.production of the hydrogen bomb.
 It is also used as a radioactiveIt is also used as a radioactive
agent in making luminous paintsagent in making luminous paints
and as a tracer isotope.and as a tracer isotope.

Forms of hydrogenForms of hydrogen
 Quite apart from isotopes,Quite apart from isotopes,
hydrogen gas is a mixture of twohydrogen gas is a mixture of two
kinds of molecules, known askinds of molecules, known as
ortho- and para-hydrogen.ortho- and para-hydrogen.
 They differ from one another byThey differ from one another by
the spins of their electrons andthe spins of their electrons and
nuclei.nuclei.
 Normal hydrogen at roomNormal hydrogen at room
temperature contains 25% of thetemperature contains 25% of the
para form and 75% of the orthopara form and 75% of the ortho
form.form.

 The ortho form cannot beThe ortho form cannot be
prepared in the pure state.prepared in the pure state.
 Since the two forms differ inSince the two forms differ in
energy, the physicalenergy, the physical
properties also differ.properties also differ.
 The melting and boiling pointsThe melting and boiling points
of parahydrogen are about 0.1of parahydrogen are about 0.1
deg C lower than those ofdeg C lower than those of
normal hydrogen.normal hydrogen.

Heavy waterHeavy water
 is a form of water in whichis a form of water in which
both the hydrogen atoms areboth the hydrogen atoms are
replaced by deuterium (2H, orreplaced by deuterium (2H, or
D)D)
 The formula for "heavy water"The formula for "heavy water"
is D2O.is D2O.
 It is highly toxic to mammals.It is highly toxic to mammals.
 Some bacteria are known toSome bacteria are known to
metabolise molecular hydrogenmetabolise molecular hydrogen
(H2).(H2).

Liquid hydrogenLiquid hydrogen
 Liquid hydrogen isLiquid hydrogen is
important in cryrogenicsimportant in cryrogenics
and in the study ofand in the study of
superconductivity, as itssuperconductivity, as its
melting point is only 20melting point is only 20
degrees above absolutedegrees above absolute
zero.zero.

Binary CompoundsBinary Compounds
 some binary compoundssome binary compounds
exists with halogens (knownexists with halogens (known
as halides),as halides),
 oxygen (known as oxides),oxygen (known as oxides),
 hydrogen (known as hydrides),hydrogen (known as hydrides),
and some other compounds ofand some other compounds of
hydrogen.hydrogen.

Hydrogen exists in nature asHydrogen exists in nature as
 Hydrides-Hydrides-The term hydride is used toThe term hydride is used to
indicate compounds of the type MxHyindicate compounds of the type MxHy
 Fluorides-Fluorides- HF: hydrogen (I) fluorideHF: hydrogen (I) fluoride
 Chlorides-Chlorides- HCl: hydrogen (I) chlorideHCl: hydrogen (I) chloride
 Bromides-Bromides- HBr: hydrogen (I) bromideHBr: hydrogen (I) bromide
 Iodides-Iodides- HI: hydrogen (I) iodideHI: hydrogen (I) iodide

 Oxides- H2O: hydrogen (I) oxideOxides- H2O: hydrogen (I) oxide
 Sulfides- H2S: hydrogen (I) sulphide ,Sulfides- H2S: hydrogen (I) sulphide ,
H2S2: hydrogen (I) persulphideH2S2: hydrogen (I) persulphide
 Selenides-H2Se: hydrogen (I) selenideSelenides-H2Se: hydrogen (I) selenide
 Tellurides-H2Te: hydrogen (I) tellurideTellurides-H2Te: hydrogen (I) telluride
 Nitrides- NH3: hydrogen (I) nitrideNitrides- NH3: hydrogen (I) nitride
Hydrogen exists inHydrogen exists in
nature asnature as

 On earth,On earth,
hydrogenhydrogen
occurs chieflyoccurs chiefly
in combinationin combination
with oxygen towith oxygen to
form waterform water
moleculesmolecules

WaterWater
moleculemolecule
Hydrogen asHydrogen as
water (H2O)water (H2O)
is absolutelyis absolutely
essential toessential to
life and it islife and it is
present in allpresent in all
organicorganic
compounds.compounds.

Hydrogen and hydroxideHydrogen and hydroxide
 Water tends toWater tends to
disassociate into H+ anddisassociate into H+ and
OH- ions.OH- ions.
 In this disassociation, theIn this disassociation, the
oxygen retains theoxygen retains the
electrons and only one ofelectrons and only one of
the hydrogens, becoming athe hydrogens, becoming a
negatively charged ionnegatively charged ion
known as hydroxide.known as hydroxide.

pH – hydrogen ion concentrationpH – hydrogen ion concentration
 The chemical parameterThe chemical parameter
pH – refers to the hydrogenpH – refers to the hydrogen
ion conc. Of a solution likeion conc. Of a solution like
water.water.
 Let us see the pH of someLet us see the pH of some
common solutions in life.common solutions in life.

 Pure water has the same number (orPure water has the same number (or
concentration) of H+ as OH- ions.concentration) of H+ as OH- ions.
 Acidic solutions have more H+ ionsAcidic solutions have more H+ ions
than OH- ions.than OH- ions.
 Basic solutions have the oppositeBasic solutions have the opposite
characters.characters.
 An acid causes an increase in theAn acid causes an increase in the
numbers of H+ ions and a basenumbers of H+ ions and a base
causes an increase in the numberscauses an increase in the numbers
of OH- ions.of OH- ions.

HydrocarbonsHydrocarbons
 Molecules made up of HydrogenMolecules made up of Hydrogen
and Carbon are known asand Carbon are known as
hydrocarbons.hydrocarbons.
 They are the building blocks of lifeThey are the building blocks of life
forms and matter.forms and matter.
 A casual look at the formulas andA casual look at the formulas and
structural representations ofstructural representations of
several simple organic moleculesseveral simple organic molecules
can clearly show the role ofcan clearly show the role of
hydrogen in organic matter.hydrogen in organic matter.

Hydrogen in organic matterHydrogen in organic matter
 In the organic world, hydrogen isIn the organic world, hydrogen is
present aspresent as
 living plants and animals asliving plants and animals as
tissues,tissues,
 Acids and basesAcids and bases
 petroleum,petroleum,
 Natural gas,Natural gas,
 coal, etc.coal, etc.

Organic moleculesOrganic molecules
 Organic molecules are those that:Organic molecules are those that:
 1) formed by the actions of living1) formed by the actions of living
things; and/orthings; and/or
 2) have a carbon backbone.2) have a carbon backbone.
 Methane (CH4) is an example ofMethane (CH4) is an example of
this.this.

 The building block of anyThe building block of any
protein is the aminoprotein is the amino
acid, which has anacid, which has an
amino end (NH2) and aamino end (NH2) and a
carboxyl end (COOH).carboxyl end (COOH).

 If we remove the H from oneIf we remove the H from one
of the methane units, andof the methane units, and
begin linking them up, whilebegin linking them up, while
removing other H units, weremoving other H units, we
begin to form an organicbegin to form an organic
molecule.molecule.
 When two methane areWhen two methane are
combined, the resultantcombined, the resultant
molecule is Ethane, which hasmolecule is Ethane, which has
a chemical formula C2H6.a chemical formula C2H6.

Hydrogen is a constituent ofHydrogen is a constituent of
methane and ethanemethane and ethane

It is a part of Ethylene and benzeneIt is a part of Ethylene and benzene

It is a part of the functional groups ofIt is a part of the functional groups of
alcohols, amines, aldehydes andalcohols, amines, aldehydes and
ketonesketones

Almost all sugars contain hydrogenAlmost all sugars contain hydrogen

Glucose, maltose, sucrose andGlucose, maltose, sucrose and
fructose all show the structuralfructose all show the structural
relationships with hydrogenrelationships with hydrogen

Hydrogen is preparedHydrogen is prepared
by one of theseby one of these
methodsmethods steam on heated carbonsteam on heated carbon
 decomposition of certaindecomposition of certain
hydrocarbons with heathydrocarbons with heat
 action of sodium or potassiumaction of sodium or potassium
hydroxide on aluminumhydroxide on aluminum
 electrolysis of water, orelectrolysis of water, or
 displacement from acids bydisplacement from acids by
certain metals.certain metals.

 H2 production from crops
is a sustainable zero
carbon route.
 Carbohydrates in crops can
be fermented by anaerobic
micro-organisms to
produce H2 and CO2.
 This is a cyclic process.

 Hydrogen can be produced
through dark fermentation of
carbohydrate rich substrates,
such as crops, and methane can
be produced in a methanogenic
second stage.
 Dark fermentation to hydrogen is
a technology that could be
managed and operated at farm
scale, as is already the case with
anaerobic digestion to methane.

Fermentative hydrogen productionFermentative hydrogen production

Production of hydrogenProduction of hydrogen
 There are many industrial methods forThere are many industrial methods for
the production of hydrogen and thatthe production of hydrogen and that
used will depend upon local factorsused will depend upon local factors
such as the quantity required and thesuch as the quantity required and the
raw materials used.raw materials used.
 Two processes in use involve heatingTwo processes in use involve heating
coke with steam in the water gas shiftcoke with steam in the water gas shift
reaction or hydrocarbons such asreaction or hydrocarbons such as
methane with steam.methane with steam.
 CH4 + H2O (1100°C) → CO + 3H2CH4 + H2O (1100°C) → CO + 3H2
 C(coke) + H2O (1000°C) → CO + H2C(coke) + H2O (1000°C) → CO + H2

 In both these cases, furtherIn both these cases, further
hydrogen may be made by passinghydrogen may be made by passing
the Cobalt oxide- CO and steamthe Cobalt oxide- CO and steam
over hot (400°C) iron oxide orover hot (400°C) iron oxide or
cobalt oxide.cobalt oxide.
 CO + H2O → CO2 + H2CO + H2O → CO2 + H2

IsolationIsolation
 Hydrogen can be isolated in theHydrogen can be isolated in the
lab.lab.
 A small amount of hydrogen gasA small amount of hydrogen gas
may be made by the reaction ofmay be made by the reaction of
calcium hydride( CaH2 ) withcalcium hydride( CaH2 ) with
water.water.
 CaH2 + 2H2O → Ca(OH)2 + 2H2CaH2 + 2H2O → Ca(OH)2 + 2H2
 This is quite efficient in the senseThis is quite efficient in the sense
that 50% of the hydrogenthat 50% of the hydrogen
produced comes from water.produced comes from water.

 Another very convenientAnother very convenient
laboratory scale experimentlaboratory scale experiment
follows Boyle's earlyfollows Boyle's early
synthesis, the reaction of ironsynthesis, the reaction of iron
filings with dilute sulphuricfilings with dilute sulphuric
acid.acid.
 Fe + H2SO4 → FeSO4 + H2Fe + H2SO4 → FeSO4 + H2

 Producing hydrogen gas fromProducing hydrogen gas from
volatile hydrocarbons such asvolatile hydrocarbons such as
methane, propane, or gasoline ismethane, propane, or gasoline is
done in a "reforming" processdone in a "reforming" process
where the hydrocarbons arewhere the hydrocarbons are
reacted with steam over a nickelreacted with steam over a nickel
catalyst at 700-1000 degreescatalyst at 700-1000 degrees
Celsius.Celsius.
PRODUCINGPRODUCING
HYDROGENHYDROGEN

 A typical reaction would be:A typical reaction would be:
CH4 + H2O ---> CO + 3H2CH4 + H2O ---> CO + 3H2
methane steam carbon hydrogenmethane steam carbon hydrogen
monoxidemonoxide
 The products of this reaction areThe products of this reaction are
carbon monoxide and hydrogencarbon monoxide and hydrogen
gas.gas.

 The carbon monoxide can then beThe carbon monoxide can then be
reacted with steam over an ironreacted with steam over an iron
oxide catalyst at 350 degreesoxide catalyst at 350 degrees
Celsius to produce carbon dioxideCelsius to produce carbon dioxide
and more hydrogen gas:and more hydrogen gas:
CO     +   H20   --->   CO2    +    H2CO     +   H20   --->   CO2    +    H2
  carbon      steam        carbon    hydrogen  carbon      steam        carbon    hydrogen
monoxide                  dioxide monoxide                  dioxide
PRODUCINGPRODUCING
HYDROGENHYDROGEN

 So the net products of these twoSo the net products of these two
reactions are hydrogen gas andreactions are hydrogen gas and
carbon dioxide.carbon dioxide.
 Carbon dioxide has become anCarbon dioxide has become an
object of concern because it is aobject of concern because it is a
greenhouse gas.greenhouse gas.
PRODUCINGPRODUCING
HYDROGENHYDROGEN

 Human contributions ofHuman contributions of
greenhouse gasses to thegreenhouse gasses to the
atmosphere have alteredatmosphere have altered
its composition, and thisits composition, and this
may have a long-termmay have a long-term
effect on the globaleffect on the global
climate.climate.

Uses of hydrogenUses of hydrogen
 commercial fixation of nitrogen fromcommercial fixation of nitrogen from
the air in the Haber ammonia processthe air in the Haber ammonia process
 hydrogenation of fats and oilshydrogenation of fats and oils
 methanol production, in hydro-de--methanol production, in hydro-de--
alkylation, hydro-cracking, and hydro-alkylation, hydro-cracking, and hydro-
de-sulphurizationde-sulphurization
 rocket fuelrocket fuel
 weldingwelding
 production of hydrochloric acidproduction of hydrochloric acid
 reduction of metallic oresreduction of metallic ores

Hydrogen is also usedHydrogen is also used
 for filling balloons (hydrogen gasfor filling balloons (hydrogen gas
much lighter than air; however itmuch lighter than air; however it
ignites easily)ignites easily)
 liquid H2 is important in the studyliquid H2 is important in the study
of superconductivity since itsof superconductivity since its
melting point is only just abovemelting point is only just above
absolute zeroabsolute zero

Hazards and RisksHazards and Risks
 There are also some hazards andThere are also some hazards and
risks associated with hydrogen.risks associated with hydrogen.
 Hydrogen gas is not toxic but isHydrogen gas is not toxic but is
dangerous if mixed with air ordangerous if mixed with air or
oxygen because of the fire andoxygen because of the fire and
explosion risk.explosion risk.
 In principle, it can asphyxiateIn principle, it can asphyxiate
through denying the body accessthrough denying the body access
to oxygen.to oxygen.

HCl and Sulphuric acidHCl and Sulphuric acid
 Hydrogen chloride gas may beHydrogen chloride gas may be
made in the laboratory by themade in the laboratory by the
reaction of concentratedreaction of concentrated
sulphuric acid upon sodiumsulphuric acid upon sodium
chloride or by the reaction ofchloride or by the reaction of
concentrated sulphuric acid uponconcentrated sulphuric acid upon
concentrated hydrochloric acid.concentrated hydrochloric acid.
 In the latter case this involvesIn the latter case this involves
adding hydrochloric acid toadding hydrochloric acid to
sulphuric acid and collecting thesulphuric acid and collecting the
evolved hydrogen chloride gas.evolved hydrogen chloride gas.
The yield is around 80%.The yield is around 80%.

 NaCl(s) + H2SO4 → HCl(g) +NaCl(s) + H2SO4 → HCl(g) +
NaHSO4(s)NaHSO4(s)
 HCl(aq) + H2SO4 → HCl(g) +HCl(aq) + H2SO4 → HCl(g) +
H2SO4(aq)H2SO4(aq)
 The first of these routes isThe first of these routes is
used in industry, whereused in industry, where
temperatures of about 150°Ctemperatures of about 150°C
are used.are used.
 Crude hydrogen chloride gasCrude hydrogen chloride gas
is an important byproduct ofis an important byproduct of
the organic chemicalsthe organic chemicals
industries.industries.

Hydrogen sulphideHydrogen sulphide
 Hydrogen sulphide may be madeHydrogen sulphide may be made
in the laboratory by the reactionin the laboratory by the reaction
of calcium(II) sulphide,of calcium(II) sulphide,
magnesium(II) chloride, andmagnesium(II) chloride, and
water.water.
 The hydrogen(I) sulphide isThe hydrogen(I) sulphide is
collected by condensation.collected by condensation.
 The yield is about 80%.The yield is about 80%.
 CaS + MgCl2 + 2H2O → CaCl2 +CaS + MgCl2 + 2H2O → CaCl2 +
Mg(OH)2 + H2SMg(OH)2 + H2S

 Other routes include the reactionOther routes include the reaction
between iron(II) sulphide andbetween iron(II) sulphide and
dilute hydrochloric acid, or thedilute hydrochloric acid, or the
direct reaction between thedirect reaction between the
elements at high temperatures.elements at high temperatures.
 2HCl + FeS → Fe2+(aq) + 2Cl-(aq) +2HCl + FeS → Fe2+(aq) + 2Cl-(aq) +
H2SH2S
 8H2 + S8 (600°C) → 8H2S8H2 + S8 (600°C) → 8H2S

RadiiRadii
 There are several ways to defineThere are several ways to define
radius for atoms and ions.radius for atoms and ions.
 Atomic radii are expressed in pmAtomic radii are expressed in pm
(picometres).(picometres).
 Conversion factors are:Conversion factors are:
 1 pm = 1 x 10^-12 metre (meter)1 pm = 1 x 10^-12 metre (meter)
 100 pm = 1 Ångstrom100 pm = 1 Ångstrom
 1000 pm = 1 nanometre (nm,1000 pm = 1 nanometre (nm,
nanometer)nanometer)

HYDROGEN has manyHYDROGEN has many
usesuses
 The biggest industrial use of hydrogenThe biggest industrial use of hydrogen
is in the production of ammonia (NH3).is in the production of ammonia (NH3).
 This consumes about 42 percent of theThis consumes about 42 percent of the
hydrogen produced.hydrogen produced.
 Another 38 percent is used inAnother 38 percent is used in
petroleum refining.petroleum refining.
 Of the remainder, a significant fractionOf the remainder, a significant fraction
is used in food processing, includingis used in food processing, including
the production of hydrogenated oilsthe production of hydrogenated oils
such as margarine.such as margarine.
 Liquid hydrogen is used as a rocketLiquid hydrogen is used as a rocket
fuel.fuel.

Pure hydrogen gasPure hydrogen gas
 Pure hydrogen gas, oncePure hydrogen gas, once
obtained, burns very cleanly.obtained, burns very cleanly.
 Whereas hydrocarbon fossil fuelsWhereas hydrocarbon fossil fuels
produce carbon dioxide, carbonproduce carbon dioxide, carbon
monoxide, and oxides of nitrogenmonoxide, and oxides of nitrogen
when burned.when burned.
 Hydrogen's only combustionHydrogen's only combustion
product is water vapor.product is water vapor.

 For this reason, technologies areFor this reason, technologies are
being developed to use hydrogenbeing developed to use hydrogen
in place of fossil fuels.in place of fossil fuels.
 But it must be understood that,But it must be understood that,
unlike fossil fuels, hydrogen is notunlike fossil fuels, hydrogen is not
a source of energy, merely aa source of energy, merely a
means of transporting and storingmeans of transporting and storing
energy.energy.

Very expensiveVery expensive
 It takes energy to make hydrogen in itsIt takes energy to make hydrogen in its
pure formpure form (whether by electrolysis of(whether by electrolysis of
water, which uses electricity, or fromwater, which uses electricity, or from
the reforming of hydrocarbons, whichthe reforming of hydrocarbons, which
requires heat),requires heat), andand
 that energy must be supplied by somethat energy must be supplied by some
other source.other source.
 So, the use of hydrogen shiftsSo, the use of hydrogen shifts
environmental costs further upstream.environmental costs further upstream.

 Consideration is being given to anConsideration is being given to an
entire economy based on solar-entire economy based on solar-
and nuclear-generated hydrogen.and nuclear-generated hydrogen.
 Public acceptance,Public acceptance,
 high capital investment, andhigh capital investment, and
 the high cost of hydrogen withthe high cost of hydrogen with
respect to today's fuels are but arespect to today's fuels are but a
few of the problems facing suchfew of the problems facing such
an economy.an economy.
HYDROGEN ECONOMY

Pollution free hydrogenPollution free hydrogen
 power plants would electrolyzepower plants would electrolyze
sea water and produce hydrogen.sea water and produce hydrogen.
 The hydrogen produced can beThe hydrogen produced can be
taken to cities by pipelines.taken to cities by pipelines.
 Pollution-free hydrogen couldPollution-free hydrogen could
replace the other natural gas,replace the other natural gas,
gasoline, etc., andgasoline, etc., and
 could serve as a reducing agent incould serve as a reducing agent in
metallurgy, chemical processing,metallurgy, chemical processing,
refining, etc.refining, etc.

 It could also be used toIt could also be used to
convert trash into methaneconvert trash into methane
and ethylene.and ethylene.
 These are some of theThese are some of the
possible routes ofpossible routes of
development.development.

 The main advantage of hydrogen is that itThe main advantage of hydrogen is that it
produces no polluting emissions at theproduces no polluting emissions at the
place where it is put to its final end use.place where it is put to its final end use.
 It is like electricity in this respect;It is like electricity in this respect;
 we burn coal some place far away towe burn coal some place far away to
generate electricity, which we then usegenerate electricity, which we then use
in our homes without local pollution.in our homes without local pollution.
 But unlike electricity, hydrogen is a formBut unlike electricity, hydrogen is a form
of clean energy that can be stored.of clean energy that can be stored.
 Because we do not yet have means forBecause we do not yet have means for
storing large amounts of electricity, itstoring large amounts of electricity, it
must be used as soon as it is generated,must be used as soon as it is generated,
and this leads to various inefficiencies.and this leads to various inefficiencies.

 Hydrogen is a versatile
energy carrier that can be
used to power nearly
every end-use energy
need.
 The fuel cell — an energy
conversion device that
can efficiently capture
and use the power of
hydrogen — is the key to

 Stationary fuel cells can be used
for backup power, power for
remote locations, distributed power
generation, and cogeneration (in
which excess heat released during
electricity generation is used for
other applications).
 Fuel cells can power almost any
portable application that typically
uses batteries, from hand-held
devices to portable generators.

Fuel cells can also power our
transportation, including personal
vehicles, trucks, buses, and marine
vessels, as well as provide auxiliary
power to traditional transportation
technologies.
Hydrogen can play a particularly
important role in the future by
replacing the imported petroleum we
currently use in our cars and trucks.

Fuel cells directly
convert the chemical
energy in hydrogen to
electricity, with pure
water and potentially
useful heat as the only
byproducts.

Hydrogen-powered fuel
cells are not only
pollution-free, but also
can have two to three
times the efficiency of
traditional combustion
technologies.

 A conventional
combustion-based power
plant typically generates
electricity at efficiencies of
33 to 35 percent, while fuel
cell systems can generate
electricity at efficiencies
up to 60 percent (and even
higher with cogeneration).

 The gasoline engine in a conventional
car is less than 20% efficient in
converting the chemical energy in
gasoline into power that moves the
vehicle, under normal driving conditions.
 Hydrogen fuel cell vehicles, which use
electric motors, are much more energy
efficient and use 40-60 percent of the
fuel’s energy — corresponding to more
than a 50% reduction in fuel
consumption, compared to a
conventional vehicle with a gasoline
internal combustion engine.
 In addition, fuel cells operate quietly,
have fewer moving parts, and are well
suited to a variety of applications.

 Hydrogen is an energy carrier, not
an energy source, meaning that it
stores and delivers energy in a
usable form.
 Hydrogen can be produced using
abundant and diverse domestic
energy resources, including fossil
fuels, such as natural gas and
coal; renewable energy resources,
such as solar, wind, and biomass;
and nuclear energy.

 Using hydrogen as a form of
energy can not only reduce our
dependence on imported oil, but
also benefit the environment by
reducing emissions of greenhouse
gases and criteria pollutants that
affect our air quality.

What Are the Challenges?
 Hydrogen has a very high energy
content by weight (about three
times more than gasoline), but it
has a very low energy content by
volume (about four times less than
gasoline).
 This makes hydrogen a challenge
to store, particularly within the
size and weight constraints of a
vehicle.

hydrogen as a form of energy
 Developing safe, reliable, compact, and
cost-effective hydrogen storage
technologies is one of the most
technically challenging barriers to the
widespread use of hydrogen as a form
of energy.
 To be competitive with conventional
vehicles, hydrogen-powered cars must
be able to travel more than 500km
between fills.

 Hydrogen (H2) is widely regarded as a
key component in future energy
systems because it is a sustainable,
clean, and transportable energy
carrier.
 It can be generated from pure water,
and burned to produce nothing but
water.
 Thus if hydrogen generated using clean
and sustainable processes replaces
fossil fuels as our main energy carrier,
we will have significantly lower
emissions of greenhouse gases,
especially carbon dioxide (CO2), and
air pollutants, notably nitrogen oxides
and volatile organic compounds.

 It is important to assess the overall
impact of hydrogen on the
environment.
 The environment is a complex, highly
coupled, non-linear system which may
react in unforeseen ways to changes in
the status quo.
 Emissions of man-made compounds
including CFCs, which destroy ozone
and act as greenhouse gases, other
halogenated compounds and of course
carbon dioxide have already caused
environmental problems.
 We should not repeat the same
mistakes with hydrogen.

Sources, sinks and concentrations
of atmospheric hydrogen
 The (incomplete) combustion
of fossil fuel and biomass in
boilers and internal
combustion engines generates
hydrogen along with carbon
monoxide and carbon dioxide.
 At present, this source
accounts for about 40% of all
the hydrogen released into the
atmosphere.

 Another important source,
accounting for an estimated
50% of atmospheric hydrogen
emissions, is the atmospheric
photochemical oxidation of
methane (CH4) and non-
methane hydrocarbons
(NMHCs).
 Emissions from volcanoes,
oceans and nitrogen-fixing
legumes account for the
remaining 10%.

 Movement of hydrogen into the upper
atmosphere and then to space is
negligible in terms of the global
hydrogen budget.
 Instead, hydrogen is removed from the
atmosphere largely through dry
deposition at the surface and
subsequent microbiological uptake in
soils.
 The rate of uptake depends on
microbial activity, soil texture and
moisture content. This accounts about
75%.

 The remaining 25% of hydrogen is
removed through oxidation by hydroxyl
free radicals (OH) in the atmosphere:
 H2 + OH → H + H2O
 H + O2 + M → HO2 + M
 The hydrogen peroxy radical (HO2)
produced continues to react with
nitrogen oxide (NO), a key step in
photochemical ozone formation or it
reacts with itself or other peroxy
radicals, thereby terminating the
photochemical oxidation chain.

 Measurements from ground
stations, balloons and
research aircrafts typically
find about 0.5 ppmv (parts
per million by volume) of
hydrogen in the
troposphere and
 0.4-0.5 ppmv in the
stratosphere

 Many hydrogen compounds, such asMany hydrogen compounds, such as
ammonia, ethyl alcohol, and hydrogenammonia, ethyl alcohol, and hydrogen
peroxide, have extensive industrial uses.peroxide, have extensive industrial uses.
 Hydrogen is widely used to recover someHydrogen is widely used to recover some
metals from their compounds because it ismetals from their compounds because it is
a good reducing agent.a good reducing agent.
 In other words, hydrogen can withdrawIn other words, hydrogen can withdraw
oxygen and other nonmetallic elementsoxygen and other nonmetallic elements
from metallic compounds, leaving a purefrom metallic compounds, leaving a pure
metal.metal.

 In New York City, a power plantIn New York City, a power plant
uses hydrogen fuel to produceuses hydrogen fuel to produce
electricity.electricity.
 Engineers have builtEngineers have built
experimental cars that run onexperimental cars that run on
hydrogen fuel.hydrogen fuel.
 By chemically adding hydrogenBy chemically adding hydrogen
to coal, coal can be convertedto coal, coal can be converted
into petrol, fuel oil, or syntheticinto petrol, fuel oil, or synthetic
natural gasnatural gas

Uses of HydrogenUses of Hydrogen
 The most important use ofThe most important use of
hydrogen is the ammoniahydrogen is the ammonia
synthesis.synthesis.
 The use of hydrogen is extendingThe use of hydrogen is extending
quickly in fuel refinement, like thequickly in fuel refinement, like the
breaking down by hydrogenbreaking down by hydrogen
(hydrocracking), and in sulphur(hydrocracking), and in sulphur
elimination.elimination.

Uses of HydrogenUses of Hydrogen
 Huge quantities of hydrogen areHuge quantities of hydrogen are
consumed in the catalyticconsumed in the catalytic
hydrogenation of unsaturatedhydrogenation of unsaturated
vegetable oils to obtain solid fat.vegetable oils to obtain solid fat.

 Hydrogenation is used in theHydrogenation is used in the
manufacture of organic chemicalmanufacture of organic chemical
products.products.
 Huge quantities of hydrogen areHuge quantities of hydrogen are
used as rocket fuels, inused as rocket fuels, in
combination with oxygen or fluor,combination with oxygen or fluor,
and as a rocket propellentand as a rocket propellent
propelled by nuclear energy.propelled by nuclear energy.

 Hydrogen is the most flammableHydrogen is the most flammable
of all the known substances.of all the known substances.
 Hydrogen is slightly more solubleHydrogen is slightly more soluble
in organic solvents than in water.in organic solvents than in water.
 Many metals absorb hydrogen.Many metals absorb hydrogen.
 Hydrogen absorption by steel canHydrogen absorption by steel can
result in brittle steel, which leadsresult in brittle steel, which leads
to fails in the chemical processto fails in the chemical process
equipment.equipment.

 At normal temperature hydrogenAt normal temperature hydrogen
is a not very reactive substance,is a not very reactive substance,
unless it has been activatedunless it has been activated
somehow; for instance, by ansomehow; for instance, by an
appropriate catalyser.appropriate catalyser.
 At high temperatures it’s highlyAt high temperatures it’s highly
reactive.reactive.

 Although in general it’s diatomic,Although in general it’s diatomic,
molecular hydrogen dissociatesmolecular hydrogen dissociates
into free atoms at highinto free atoms at high
temperatures.temperatures.
 Atomic hydrogen is a powerfulAtomic hydrogen is a powerful
reductive agent, even at ambientreductive agent, even at ambient
temperature.temperature.
 It reacts with the oxides andIt reacts with the oxides and
chlorides of many metals, likechlorides of many metals, like
silver, copper, lead, bismuth andsilver, copper, lead, bismuth and
mercury, to produce free metals.mercury, to produce free metals.

 It reduces some salts to theirIt reduces some salts to their
metallic state, like nitrates,metallic state, like nitrates,
nitrites and sodium and potassiumnitrites and sodium and potassium
cyanide.cyanide.

 The heat released when theThe heat released when the
hydrogen atoms recombine tohydrogen atoms recombine to
form the hydrogen moleculesform the hydrogen molecules
is used to obtain highis used to obtain high
temperatures in atomictemperatures in atomic
hydrogen welding.hydrogen welding.

Health effects of hydrogen Health effects of hydrogen
 Effects of exposure to hydrogen:Effects of exposure to hydrogen:
 Fire: Extremely flammable. ManyFire: Extremely flammable. Many
reactions may cause fire orreactions may cause fire or
explosion.explosion.
 Explosion: Gas/air mixtures areExplosion: Gas/air mixtures are
explosive.explosive.
 Routes of exposure:Routes of exposure: TheThe
substance can be absorbed intosubstance can be absorbed into
the body by inhalation.the body by inhalation.

 Physical dangers:Physical dangers:
 The gas mixes well with air, explosiveThe gas mixes well with air, explosive
mixtures are easily formed. The gas ismixtures are easily formed. The gas is
lighter than air.lighter than air.
 CChemical dangers:hemical dangers: Heating may causeHeating may cause
violent combustion or explosion.violent combustion or explosion.
Reacts violently with air, oxygen,Reacts violently with air, oxygen,
halogens and strong oxidants causinghalogens and strong oxidants causing
fire and explosion hazard.fire and explosion hazard.
 Metal catalysts, such as platinum andMetal catalysts, such as platinum and
nickel, greatly enhance thesenickel, greatly enhance these
reactions.reactions.

 Inhalation: High concentrations of thisInhalation: High concentrations of this
gas can cause an oxygen-deficientgas can cause an oxygen-deficient
environment.environment.
 Individuals breathing such anIndividuals breathing such an
atmosphere may experience symptomsatmosphere may experience symptoms
which include headaches, ringing inwhich include headaches, ringing in
ears, dizziness, drowsiness,ears, dizziness, drowsiness,
unconsciousness, nausea, vomitingunconsciousness, nausea, vomiting
and depression of all the senses.and depression of all the senses.
 The skin of a victim may have a blueThe skin of a victim may have a blue
color.color.

Jules Verne, 1874Jules Verne, 1874
 ““ I believe that water will one dayI believe that water will one day
be employed as a fuel; thatbe employed as a fuel; that
hydrogen or oxygen whichhydrogen or oxygen which
constitute it, used singly orconstitute it, used singly or
together, will furnish astogether, will furnish as
inexhaustible source of heat andinexhaustible source of heat and
light”.light”.
 Hydrogen has a lot to do for man-Hydrogen has a lot to do for man-
kind and environment.kind and environment.

Hydrogen and its importance

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