IT CONTAINS ALL INFORMATION REGARDING TO HYDROGEN
THE PROJECT IS MADE FOR SEMINAR OF CHEMISTRY OF MOLEDINA JUNIOR COLLEGE , PUNE. FROM THE STUDENT OF 11TH SCIENCE, SPECIALLY EFFORTS OF SHAHRUKH ISAQUE PATHAN.
INTRODUCTION Hydrogen, chemical element that exists as a gas at room temperature. When hydrogen gas burns in air, it forms water. French chemist Antoine Lavoisier named hydrogen from the Greek words for ―water former.‖ Hydrogen has the smallest atoms of any element. A hydrogen atom contains one proton, and only one electron . The proton is the center, or nucleus, of the hydrogen atom, and the electron travels around the nucleus. Pure hydrogen exists as hydrogen gas, in which pairs of hydrogen atoms bond together to make molecules.
HOW WAS HYDRGOEN FOUND Discovered by Henry Cavendish Hydrogen was discovered in London It was discovered in the year of 1766
The hydrogen atomconsisting the protonin the centre or thenucleus of the hydro-gen atom and the ele-ctron travelling aroun-d the nucleus.
POSITION IN THE PERIODIC TABLE Hydrogen is the first element in the periodic table of the elements and is represented by the symbol H. Hydrogen, with only one proton, is the simplest element. It is usually placed in Period 1 and Group 1 of the periodic table. Hydrogen can combine chemically with almost every other element and forms more compounds than does any other element. These compounds include water, minerals, and hydrocarbons—compounds made of hydrogen and carbon—such as petroleum and natural gas.
How is Hydrogen Produced? Reforming fossil fuels Heat hydrocarbons with steam Produce H2 and CO Electrolysis of water Use electricity to split water into O2 and H2 High Temperature Electrolysis Experimental Biological processes Very common in nature Experimental in laboratories
STEAM REFORMING From any hydrocarbon Natural gas typically used Water (steam) and hydrocarbon mixed at high temperature (700–1100 °C) Steam (H2O) reacts with methane (CH4) CH4 + H2O → CO + 3 H2 - 191.7 kJ/mol The thermodynamic efficiency comparable to (or worse than) an internal combustion engine Difficult to motivate investment in technology
CARBON MONOXIDE REFORMING Additional hydrogen can be recovered using carbon monoxide (CO) low-temp (130°C) water gas shift reaction CO + H2O → CO2 + H2 + 40.4 kJ/mol Oxygen (O) atom stripped from steam Oxidizes the carbon (C) Liberates hydrogen bound to C and O2
High Temperature Electrolysis Electrolysis at high temperatures Use less energy to split water
Biological H2 Creation Nature has very simple methods to split water Scientists are working to mimic these processes in the lab; then commercially
PHYSICAL PROPERTIES OF H2 Dihydrogen is a : Colourless , Odourless Tasteless Combustible gas Lighter than air Insoluble in water It‘s melting point – 18.73 K & boiling point – 23.67 K
CHEMICAL PROPERTIES OF H2 Hydrogen gas does not usually react with other chemicals at room temperature, because the bond between the hydrogen atoms is very strong and can only be broken with a large amount of energy. Since its orbital is incomplete with 1s1 electronic configuration, it does combine with almost all the elements . It accomplishes reactions by: 1.loss of one e- to give H+ 2.gain of an e- to form H- 3.sharing electrons to form a single covalent bond.
BOSCH REACTION The Bosch reaction is a chemical reaction between carbondioxide and hydrogen that produces elemental carbon (graphite), water anda 10% return of invested heat. This reaction requires the introduction ofiron as a catalyst and requires a temperature level of 530-730 degreesCelsius.The overall reaction is as follows: CO2(g) + 2 H2(g) → C(s) + 2 H2O(g) The above reaction is actually the result of two reactions. The firstreaction, the reverse water gas shift reaction, is a fast one. CO2 + H2 → CO + H2OThe second reaction controls the reaction rate. CO + H2 → C + H2O
The overall reaction produces 2.3×103 joules for every gram ofcarbon produced at 650 °C. Reaction temperatures are in the rangeof 450 to 600 °C.The reaction can be accelerated in the presence ofan iron, cobalt or nickel catalyst. Ruthenium also serves to speedup the reaction. Together with the Sabatier reaction the Bosch reaction isstudied as a way to remove carbon dioxide and to generate cleanwater aboard a space station The reaction is also used to produce graphitefor radiocarbon dating with Accelerator Mass Spectrometry. It is named after the German chemist Carl Bosch.
Hydrogenation To treat with hydrogen - is a chemical reaction betweenmolecular hydrogen (H2) and another compound or element, usually inthe presence of a catalyst. The process is commonly employedto reduce or saturate organic compounds. Hydrogenation typicallyconstitutes the addition of pairs of hydrogen atoms to a molecule,generally an alkene. Catalysts are required for the reaction to be usable;non-catalytic hydrogenation takes place only at very hightemperatures. Hydrogen adds to double and triple bonds in hydrocarbons Because of the importance of hydrogen, many related reactionshave been developed for its use. Most hydrogenations use gaseoushydrogen (H2), but some involve the alternative sources of hydrogen, notH2: these processes are called transfer hydrogenations. The reversereaction, removal of hydrogen from a molecule, is called dehydrogenation.
A reaction where bonds are broken while hydrogen is added iscalled hydrogenolysis, a reaction that may occur to carbon-carbon andcarbon-heteroatom (oxygen, nitrogen or halogen) bonds. Hydrogenationdiffers from protonation or hydride addition: in hydrogenation, theproducts have the same charge as the reactants. An illustrative example of a hydrogenation reaction is theaddition of hydrogen to maleic acid to form succinic acid. Numerousimportant applications of this petrochemical are found in pharmaceuticaland food industries. Hydrogenation of unsaturatedfats produces saturated fats and, in some cases, trans fats.
DEHYDROGENATION Dehydrogenation is a chemical reaction that involves theremoval of hydrogen from a molecule as (H2). It is the reverse processof hydrogenation. Dehydrogenation reactions may be either large scaleindustrial processes or smaller scale laboratory procedures. Classes of the reaction There are a variety of classes of dehydrogenations: •Aromatization — Six-membered alicyclic rings can be aromatized in the presence of hydrogenation catalysts, the elements sulfur and selenium, or quinones (such as DDQ). •Oxidation — The conversion of alcohols to ketones or aldehydes can be effected by metal catalysts such as copper chromite. In the Oppenauer oxidation, hydrogen is transferred from one alcohol to another to bring about the oxidation.
• Dehydrogenation of amines — amines can be convertedto nitriles using a variety of reagents, such as Iodinepentafluoride (IF5).• Dehydrogenation of paraffins and olefins — paraffins like n-pentane and isopentane can be convertedto pentene and isoprene using chromium (III) oxide as a catalyst at500 degree C. Dehydrogenation converts saturated fats to unsaturated fats.Enzymes that catalyze dehydrogenation are called dehydrogenases.Dehydrogenation processes are used extensively to produce styrene inthe fine chemicals, oleochemicals, petrochemicals, and detergentsindustries.
TRANSFER HYDROGENATIONIs the addition of hydrogen (H2; dihydrogenin inorganic and organometallic chemistry) to a molecule from a source otherthan gaseous H2. It is applied in industry and in organic synthesis, in partbecause of the inconvenience and expense of using gaseous H2. One large scaleapplication of transfer hydrogenation is coal liquefaction using "donor solvents"such as tetralin HYDROGENOLYSIS Hydrogenolysis is a chemical reaction whereby a carbon–carbon or carbon–heteroatom single bond is cleaved or undergoes "lysis" by hydrogen. The heteroatom may vary, but it usually is oxygen, nitrogen, or sulfur. A related reaction is hydrogenation, where hydrogen is added to the molecule, without cleaving bonds. Usually hydrogenolysis is conducted catalytically using hydrogen gas.
HYDROGEN STORAGE OPTIONS PHYSICAL STORAGE CHEMICAL STORAGE Molecular Dissociative H2 H2 2H REVERSIBLE REVERSIBLE NON-REVERSIBLE REFORMED FUEL HYDROLYZED FUEL DECOMPOSED FUELCOMPRESSED HYBRID LIQUID GAS TANKS HYDROGEN CONVENTIONAL COMPLEX METAL LIGHT ELEMENT METAL HYDRIDES HYDRIDES SYSTEMS
Compressed Storage Prototype vehicle tanks developed Efficient high-volume manufacturing processes needed Less expensive materials desired carbon fiber binder Evaluation of engineering factors related to safety required understanding of failure processes
Liquid Storage Prototype vehicle tanks developed Reduced mass and especially volume needed Reduced cost and development of high-volume production processes needed • Extend dormancy (time to start of ―boil off‖ loss) without increasing cost, mass, volume • Improve energy efficiency of liquefaction
Hybrid Physical Storage Compressed H2 @ cryogenic temperatures H2 density increases at lower temperatures further density increase possible through use of adsorbents – opportunity for new materials The best of both worlds, or the worst ?? Concepts under development
Non-reversible On-board Storage On-board reforming of fuels has been rejected as a source of hydrogen because of packaging and cost energy station reforming to provide compressed hydrogen is still a viable option Hydrolysis hydrides suffer from high heat rejection on-board and large energy requirements for recycle On-board decomposition of specialty fuels is a real option need desirable recycle process engineering for minimum cost and ease of use
Reversible On-board Storage Reversible, solid state, on-board storage is the ultimate goal for automotive applications Accurate, fast computational techniques needed to scan new formulations and new classes of hydrides Thermodynamics of hydride systems can be “tuned” to improve system performance storage capacity temperature of hydrogen release kinetics/speed of hydrogen refueling Catalysts and additives may also improve storage characteristics
Hydrogen has three naturallyoccurring isotopes,denoted 1H, 2H and 3H. Other,highly unstable nuclei (4H to 7H)have been synthesized in thelaboratory but not observed innature
1H1H is the most common hydrogen isotope withan abundance of more than 99.98%. Becausethe nucleus of this isotope consists of only asingle proton, it is given the descriptive butrarely used formal name protium.
2H2H, the other stable hydrogen isotope, is known as deuterium andcontains one proton and one neutron in its nucleus. Essentially alldeuterium in the universe is thought to have been produced at thetime of the Big Bang, and has endured since that time. Deuteriumis not radioactive, and does not represent a significant toxicityhazard. Water enriched in molecules that include deuteriuminstead of normal hydrogen is called heavy water. Deuterium andits compounds are used as a non-radioactive label in chemicalexperiments and in solvents for 1H-NMR spectroscopy. Heavywater is used as a neutron moderator and coolant for nuclearreactors. Deuterium is also a potential fuel forcommercial nuclear fusion
3H3H is known as tritium and contains one proton and twoneutrons in its nucleus. It is radioactive, decaying into helium-3 through beta decay with a half-life of 12.32 years. It is soradioactive that it can be used in luminous paint, making ituseful in such things as watches. The glass prevents the smallamount of radiation from getting out. Small amounts oftritium occur naturally because of the interaction of cosmicrays with atmospheric gases; tritium has also been releasedduring nuclear weapons tests. It is used in nuclear fusionreactions, as a tracer in isotope geochemistry, and specializedin self-powered lighting devices. Tritium has also been used inchemical and biological labeling experiments as a radiolabe
4H4H contains one proton and three neutrons in its nucleus. Itis a highly unstable isotope of hydrogen. It has beensynthesized in the laboratory by bombarding tritium withfast-moving deuterium nuclei. In this experiment, thetritium nuclei captured neutrons from the fast-movingdeuterium nucleus. The presence of the hydrogen-4 wasdeduced by detecting the emitted protons. Its atomicmass is 4.02781 ± 0.00011. It decays through neutronemission with a half-life of (1.39 ± 0.10) × 10−22 seconds.
5H5H is a highly unstable isotope of hydrogen. Thenucleus consists of a proton and four neutrons.It has been synthesized in the laboratory bybombarding tritium with fast-moving tritiumnuclei. In this experiment, one tritium nucleuscaptures two neutrons from the other, becominga nucleus with one proton and four neutrons.The remaining proton may be detected, and theexistence of hydrogen-5 deduced. It decaysthrough double neutron emission and has a half-life of at least 9.1 × 10−22 seconds.
6H6H decays through triple neutronemission and has a half-life of2.90×10−22 seconds. It consists of 1proton and 5 neutrons.
7H7H consists of a proton and six neutrons. It was firstsynthesized in 2003 by a group of Russian, Japaneseand French scientists at RIKENs RI Beam ScienceLaboratory by bombarding hydrogen with helium-8 atoms. In the resulting reaction, the helium-8sneutrons were donated to the hydrogens nucleus.The two remaining protons were detected by the"RIKEN telescope", a device composed of severallayers of sensors, positioned behind the target of theRI Beam cyclotron.
IMPORTANT Hydrogen is the only element that has different namesfor its isotopes in common use today. During the early study ofradioactivity, various heavy radioactive isotopes were giventheir own names, but such names are no longer used, except fordeuterium and tritium. The symbols D and T (insteadof2H and 3H) are sometimes used for deuterium and tritium,but the corresponding symbol for protium, P, is already in usefor phosphorus and thus is not available for protium. Inits nomenclatural guidelines, the International Union of Pureand Applied Chemistry allows any of D, T, 2H, and 3H to beused, although 2H and 3H are preferred.
Table:- Atomic And Physical Properties Of Isotopes HydrogenProperty Hydrogen Deuterium TritiumActive (%) 99.985 0.0156 -15Abundance 10Relative at mass 1.008 2.014 3.016Melting point 13.96 18.73 20.62Boiling point 20.39 23.67 25.0Density 0.09 0.18 0.27E of fusion 0.117 0.197 _E of vaporization 0.904 0.197 _E of dissociation 435.88 443.35 _Interneuclar dist 74.14 74.14 _Electronic gain e -73 _ _Covalent radius 37 _ _Ionic radius 208 _ _
USES OF HYDROGEN ENERGY SECURITY ECONOMIC PROSPERITY ENVIRONMENTAL STEWARDSHIP
INTERIOR OF THE SUN The Sun‘s energy is produced in the core through nuclear fusion of hydrogen atoms into helium. Gases in the core are about 150 times as dense as water and reach temperatures as high as 16 million degrees C (29 million degrees F).
Presence of hydrogen in volcanoes and in our food particles
Cont…. Hydrogen accounts for about 73 percent of the observed mass of the universe and is the most common element in the universe. Hydrogen atoms were the first atoms to form in the early universe and that the atoms of the other elements formed later from the hydrogen atoms. About 90 percent of the atoms in the universe are hydrogen, about 9 percent are helium, and all the other elements account for less than 1 percent.
Cont…. Common Molecules: Many common molecules contain hydrogen. In these molecules, butane contains ten hydrogen atoms, ammonia contains three hydrogen atoms, and water contains two hydrogen atoms.
Biomass Transportation Hydro HIGH EFFICIENCY Wind & RELIABILITY . SolarGeothermal Nuclear With Carbon Sequestration Oil Distributed ZERO/NEAR ZERO Generation EMISSIONS Coal Natural Gas
With advancement of science and technology we realize in orderto make our lives comfortable fossil fuels are depleating at analarming rate and will be exhausted soon. The electricity cannotbe stored to run automobiles. It is not possible to store andtransport nuclear energy. Hydrogen is another alternativesource of energy and hence called as ‘hydrogen economy’.Hydrogen has some advantages as fuel • Available in abundance in combined form as water. • On combustion produces H2O. Hence pollution free. • H2-O2 fuel cell give more power. • Excellent reducing agent. Therefore can be used as substitute of carbon in reduction for processes in industry.
Flexibility Of UseTransportation Desired range can be achieved with on-board hydrogen storage (unlike Battery Electric Vehicle) Can be used in internal combustion engines Trains, automobiles, buses, and shipsBuildings Combined heat, power, and fuel Reliable energy services for critical applications Grid independenceIndustrial Sector Already plays an important role as a chemical Opportunities for additional revenue streams
Storing & Transporting Hydrogen Store and Transport as a Gas Bulky gas Compressing H2 requires energy Compressed H2 has far less energy than the same volume of gasoline Store and Transport as a Solid Sodium Borohydride Calcium Hydride Lithium Hydride Sodium Hydride
Fuel Cell LifeWhile fuel cells do wearout over time, A PEMfuel cell in a vehicleshould have a 4,000hour service life, whilestationary applicationsshould last 40,000hours.
Hydrogen Safety Hydrogen Gasoline Three Second seconds Fuel leak simulation Hydrogen on left Gasoline on right Equivalent energy release One minute
Advantages of a Hydrogen Economy Waste product of burning H2 is water Elimination of fossil fuel pollution Elimination of greenhouse gases Elimination of economic dependence Distributed production The stuff of stars
Disadvantages of Hydrogen Economy Low energy densities Difficulty in handling, storage, transport Requires an entirely new infrastructure Creates CO2 if made from fossil fuels Low net energy yields Much energy needed to create hydrogen Possible environmental problems Ozone depletion (not proven at this point)
"I believe that water will one day be employed as fuel, thathydrogen and oxygen which constitute it, used singly ortogether, will furnish an inexhaustible source of heat andlight, of an intensity of which coal is not capable. I believethen that when the deposits of coal are exhausted, we shallheat and warm ourselves with water. Water will be the coalof the future." Jules Vernes (1870) L´île mystérieuse
HYDROGEN DAMAGE Hydrogen damage is the generic name given to a large numberof metal degradation processes due to interaction with hydrogen.Hydrogen is present practically everywhere, several kilometers above theearth and inside the earth. Engineering materials are exposed to hydrogen andthey may interact with it resulting in various kinds of structural damage.Damaging effects of hydrogen in metallic materials have been known since1875 when W. H. Johnson reported ―some remarkable changes producedin iron by the action of hydrogen and acids‖. During the intervening yearsmany similar effects have been observed in different structural materials,such as steel, aluminum, titanium, and zirconium. Because of thetechnological importance of hydrogen damage, many people explored thenature, causes and control measures of hydrogen related degradation ofmetals. Hardening, embrittlement and internal damage are the main hydrogendamage processes in metals. This article consists of a classification ofhydrogen damage, brief description of the various processes and theirmechanisms, and some guidelines for the control of hydrogen damage.
HYDROGEN EMBRITTLEMENT Hydrogen embrittlement is the process by which various metals, most importantly high-strength steel, become brittle and fracture following exposure to hydrogen. Hydrogen embrittlement is often the result of unintentional introduction of hydrogen into susceptible metals during forming or finishing operations and increases cracking in the material. Hydrogen embrittlement is also used to describe the formation of zircaloy hydride. Use of the term in this context is common in the nuclear industry.
HYDROGEN LEAK TESTING Hydrogen leak testing is the normal way in whicha hydrogen pressure vessel or installation is checked for leaks or flaws. Thereare various tests. The Hydrostatic test, The vessel is filled with a nearly incompressibleliquid - usually water or oil - and examined for leaks or permanent changes inshape. The test pressure is always considerably more than the operatingpressure to give a margin for safety, typically 150% of the operating pressure. The Burst test, The vessel is filled with a gas and tested for leaks. Thetest pressure is always considerably more than the operating pressure to givea margin for safety, typically 200% or more of the operating pressure.The Helium leak test, The leak detection method uses helium (the lightestinert gas) as a tracer gas and detects it in concentrations as small as one partin 10 million. The helium is selected primarily because it penetrates smallleaks readily.
Usually a vacuum inside the object is created with an externalpump connected to the instrument.Alternatively helium can be injected inside the product while theproduct itself is enclosed in a vacuum chamber connected to theinstrument. In this case Burst and leakage tests can be combined inone operation. The Hydrogen sensor, The object is filled with a mixture of5% hydrogen/ 95% nitrogen, (below 5.7% hydrogen is non-flammable (ISO-10156). This is called typically a sniffing test. The handprobe connected to the microelectronic hydrogensensors is used to check the object. An audio signal increases inproximity of a leak. Detection of leaks go down to 5x10-7 cubiccentimeters per second. Compared to the helium test: hydrogen ischeaper than helium, no need for a vacuum, the instrument could becheaper.
HYDROGEN SAFETY Hydrogen safety covers the safe production, handling and use of hydrogen. Hydrogen poses unique challenges due to its ease of leaking, low-energy ignition, wide range of combustible fuel-air mixtures, buoyancy, and its ability to embrittle metals that must be accounted for to ensure safe operation. Liquid hydrogen poses additional challenges due to its increased density and the extremely low temperatures needed to keep it in liquid form.
OCCURRENCE OF DIHYDROGEN Hydrogen is the tenth most common element on Earth. Because it is so light, though, hydrogen accounts for less than 1 percent of Earths total mass. It is usually found in compounds. Pure hydrogen gas rarely occurs in nature, although volcanoes and some oil wells release small amounts of hydrogen gas. Hydrogen is in nearly every compound in the human body. For example, it is in keratin, the main protein that forms our hair and skin, and in the enzymes that digest food in our intestines. Hydrogen is in the molecules in food that provide energy: fats, proteins, and carbohydrates.
PREPARATION OF DIHYDROGEN Laboratory preparation of dihydrogen: 1.It is usually prepared by the reaction of granulated zinc with dilute hydrochloric acid. The chemical equation for this reaction is the following: Zn + 2HCl → ZnCl2 + H2 2.It can also be prepared by the reaction of zinc with aqueous alkali. The chemical equation for this reaction is the following: Zn +2NaOH Na2ZnO2 + H2 (Sodium zincate)
Cont…. Commercial production of dihydrogen:1. Electrolysis of acidified water using platinum electrodes gives hydrogen. 2 H2O electrolysis 2H2 + O2 This chemical equation shows that two water molecules (with electricity), form two molecules of hydrogen gas and one molecule of oxygen gas.2.High purity (>99.95%) dihydrogen is obtained by electrolysing warm aqueous barium hydroxide solution between nickel electrodes.
Cont….3. It is obtained as a byproduct in the manufacture of sodium hydroxide & chlorine by the electrolysis of brine solutions . The reactions that takes place are: At anode : 2Cl- Cl2 +2e- At cathode: 2H2O + 2e- H2 + 2OH- The overall reaction is 2Na+ + 2Cl- +2H2O Cl2 + H2 + 2Na+ + 2OH-
Cont….4. Reaction of steam on hydrocarbons at high temperature in the presence of catalyst yields hydrogen. e.g., CH4 + H2O 1270K Ni CO + 3H2 The mixture of CO & H2 is called water gas. It is used for synthesis of methanol & a number of hydrocarbons, therefore it is called synthesis gas or ‘syngas’. The production of dihydrogen can be increased by reacting carbon monoxide with steam in the presence iron chromate as catalyst. CO + H2O 673K CO2 + H2 Catalyst This is called water-gas shift reaction. Carbon dioxide is removed by scrubbing with sodium arsenite solution.
CHEMISTRY OF DIHYDROGEN Reaction with halogens: It reacts with halogens, X2 to give hydrogen halides, HX, H2+X2 2HX (X= F, Cl, Br, I) While the reaction with fluorine occurs even in the dark, with iodine it requires a catalyst. Reaction with dioxygen: It reacts with dioxygen to form water. The reaction is highly exothermic. 2H2 + O2 catalyst or heating 2H2O ; H = -285.9 kJ mol-1
Cont…. Reaction with dinitrogen: With dintrogen it forms ammonia. 3H2 +N2 673K,200atm 2NH3; H=-92.6 kJ mol-1 This is the method for the manufacture of ammonia by Haber process. Haber Process: German chemist and Nobel laureate Fritz Haber developed an economical method of producing ammonia from air and seawater. In his process, nitrogen is separated from the other components of air through distillization. Hydrogen is obtained from seawater by passing an electric current through the water. The nitrogen and hydrogen are combined to form ammonia (NH3).
Cont…. Reaction with metals: Hydrogen also forms ionic bonds with some metals, at a high temperature, creating a compound called a hydride. H2 +2M 2MH Where M is an alkali metal (e.g. lithium, sodium, potassium, rubidium, cesium, and francium.) Reactions with metal ions & metal oxides: It reduces some metal ions in aqueous solution & oxides of metals (less active than iron ) into corresponding metals. H2+Pd 2+ Pd + 2H+ yH2 +MxOy xM + yH2O
Cont…. Reactions with organic compounds: 1.Hydrogenation of vegetable oils using nickel as catalyst gives edible fats. (margarine & vanaspati ghee). 2.Hydroformylation of olefins yields aldehydes which further undergo reduction to give alcohols. H2+CO+RCH=CH2 RCH2CH2CHO H2 +RCH2CH2CHO RCH2CH2CH2OH
USES OF DIHYDROGEN The largest use of dihydrogen is in the synthesis of ammonia which is used in the manufacture of nitric acid & nitrogenous fertilizers. Dihydrogen is used in the manufacture of vanaspati fat. It is used in the manufacture of bulk organic chemicals, particularly methanol. CO + 2H2 catalyst cobalt CH3OH It is widely used for the manufacture of metal hydrides. It is used for the preparation of hydrogen chloride, a highly useful chemical.
Cont…… In metallurgical processes, it is widely used to reduce heavy metal oxides to metals. Atomic hydrogen & oxy-hydrogen torches find use for cutting & welding purposes. It is used as a rocket fuel in space research. Dihydrogen is used in the fuel cells for generating electrical energy. It has many advantages over the conventional fossil fuels & electric power.
DIHYDROGEN AS A FUEL: Dihydrogen releases large quantities of heat on combustion. Dihydrogen can release more energy than petrols. HYDROGEN ECONOMY: The basic principle of hydrogen economy is the transportation & storage of energy in the form of liquid or gaseous dihydrogen. Energy is transmitted in the form of dihydrogen & not as electric power. It is also use in fuel cell for generation of electric power.
HYDRIDES Dihydrogen also forms ionic bonds with some metals, at a high temperature, creating a compound called a hydride. If E is the symbol of an element then hydride can be expressed as EHX (e.g. MgH2) or EmHn (e.g. B2H6). The hydrides are classified into three categories: 1.Ionic or saline or saltlike hydrides. 2.Covalent or molecular hydrides. 3.Metallic or non-stoichiometric hydrides.
Nearly all elements are able to form hydride compound
IONIC OR SALINE HYDRIDES These are stoichiometric compounds of dihydrogen formed with most of the s-block elements which are highly electropositive in character. Covalent character is found in the lighter metal hydrides (e.g. LiH, BeH2 & MgH2). The ionic hydrides are crystalline, non-volatile & non- conducting in solid state. Their melts conduct electricity & on electrolysis liberate dihydrogen gas at anode, which confirms the existence of H-ion. 2H-(melt) anode H2+2e- Saline hydrides react violently with water producing dihydrogen gas . NaH + H2O NaOH + H2
COVALENT OR MOLECULAR HYDRIDE Dihydrogen forms molecular compounds with most of the p-block elements. For e.g. CH4, NH3, H2O & HF. Hydrogen compounds of non metals have also been considered as hydrides. Being covalent they are volatile compounds. Molecular hydrides are further classified according to the relative number of electrons & bonds in their Lewis structure into: 1.Electron-deficient 2.Electron-precise 3.Electron-rich hydrides.
ELECTRON- ELECTRON-PRECISE ELECTRON-RICHDEFICIENT HYDRIDES HYDRIDESHYDRIDESHas few electrons for Have the required Have excess electronsLewis structure. number of electrons which are present as for Lewis structure. lone pair.Elements of group 13 Elements of group 14 Electrons of group 15-forms these forms these 17 forms suchcompounds. compounds. compounds.For e.g. Diborane For e.g. CH4. For e.g.NH3-(B2H6). has1lonepair, H2O- has 2 lone pairs.They act as Lewis They act as Lewisacids i.e. electron bases i.e. electronacceptor. donor.
METALLIC HYDRIDES These are formed by many d-block & f-block elements. The metals of group 7,8 & 9 do not form hydride. These hydrides conduct heat & electricity though not as efficiently as their parent metals do. Unlike saline hydrides, they are almost non-stoichiometric, being deficient in hydrogen. For e.g. LaH2.87 & YbH2.55. Law of constant composition does not hold good. The property of absorption of hydrogen on transition metal is widely used in catalytic reduction/hydrogenation reactions for the preparation of large number of compounds. Some of the metals can accommodate a very large volume of hydrogen & can be used as its storage media.
Water A major part of all living organisms is made up of water. Human body has about 65% & some plants have as much as 95% water. It is a crucial compound for the survival of all life forms. It is a solvent of great importance.
Physical properties of water It is a colourless & tasteless liquid. The unusual properties of water in the condensed phase (liquid & solid) are due to the presence of extensive hydrogen bonding between water molecules. Water has a higher specific heat, thermal conductivity, surface tension, dipole moment & dielectric constant when compared to other liquids. It is an excellent solvent for transportation of ions & molecules required for plant & animal metabolism. Due to hydrogen bonding with polar molecules, even covalent compounds like alcohol & carbohydrates dissolve in water.
STRUCTURE OF WATER In the gas phase water is a bent molecule with a bond angle of 104.50 , and O-H bond length of 95.7 pm. It is a highly polar molecule . In the liquid phase water molecules are associated together by hydrogen bonds. Density of water is more than that of ice.
Hydrogen Bonding in Water:Hydrogen bonds are chemical bonds that form betweenmolecules containing a hydrogen atom bonded to a stronglyelectronegative atom . Because the electronegative atompulls the electron from the hydrogen atom, the atoms forma very polar molecule, meaning one end is negativelycharged and the other end is positively charged. Hydrogenbonds form between these molecules because the negativeends of the molecules are attracted to the positive ends ofother molecules, and vice versa. Hydrogen bonding makeswater form a liquid at room temperature.
STRUCTURE OF ICE: Ice has a highly ordered three dimensional hydrogen bonded structure. Examination of ice crystals with x-rays shows that each oxygen atom is surrounded tetrahedrally by four other oxygen atoms a distance of 276pm. Hydrogen bonding gives ice a rather open type structure with wide holes. These holes can hold some other molecules of appropriate size interstitially.
Chemical properties of water Amphoteric nature: it has the ability to act as an acid as well as a base i.e., it behaves as an amphoteric substance. In the Bronsted sense it acts an acid with NH3 and a base with H2S. H2O+ NH3 OH- + NH4+ H2O+ H2S H3O++ HS- The auto-protolysis (self- ionization) of water takes place as follows: H2O +H2O H3O+ +OH- acid-1 base-2 acid-2 base-1
REDOX REACTIONS INVOLVING WATER Water can be easily reduced to dihydrogen by highly electropositive metals. 2H2O +2Na 2NaOH +H2 Thus ,it is a great source of dihydrogen. Water is oxidised to O2 during photosynthesis. 6CO2 +12H2O C6H12O6 + 6H2O +6O2 With fluorine also it is oxidised toO2. 2F2 + 2H2O 4H+ + 4F- +O2
Hydrolysis reaction Due to high dielectric constant, it has a very strong hydrating tendency. It dissolves many ionic compounds. However, certain covalent& some ionic compounds are hydrolysed in water. P4O10 +6H2O 4H3PO4 SiCl4 +2H2O SiO2 + 4HCl N3- + 3H2O NH3 +3OH-
A hydrolysis process generally involves water
HYDRATES FORMATION From aqueous solutions many salts can be crystallised as hydrated salts. Such an association of water is of different types viz., (i) coordinated water e.g., [Cr(H2O)6 ]3+ 3Cl- (ii) interstitial water e.g., BaCl2.2H2O (iii) hydrogen-bonded water e.g., [Cu(H2O)4]2+SO42-.H2O in CuSO4.5H2O
HYDROGEN PEROXIDE: Hydrogen peroxide is an important chemical used in pollution control treatment of domestic & industrial effluents. PREPARATION: It can be prepared by the following methods: 1.Acidifying barium peroxide & removing excess water by evaporation under reduced pressure gives hydrogen peroxide. BaO2.8H2O+H2SO4 BaSO4+H2O2+8H2O 2.Preoxodisulphate, obtained by electrolytic oxidation of acidified sulphate solutions at high current density, on hydrolysis yields hydrogen peroxide. 2HSO4- electrolysis HO3SOOSO3H hydrolysis 2HSO4- +2H++H2O2
Cont…. This method is now used for the laboratory preparation of D2O2. K2S2O8+2D2O 2KDSO4+D2O2 3.Industially it is prepared by the auto-oxidation of 2- alklylanthraquinols. 2-ethylanthraquinol H2O2+(oxidised product) In this case 1% H2O2 is formed. It is extracted with water & concentrated to 30% (by mass) by distillation under reduced pressure. It can be further concentrated to 85% by careful distillation under low pressure. The remaining water can be frozen out to obtain pure H2O2.
PHYSICAL PROPERTIES: The pure state H2O2 is an almost colourless liquid Meting point - 272.4K. Boiling point - 423K Vapour pressure (298K) – 1.9mmHg. H2O2 is miscible with water in all proportions & forms a hydrate H2O2.H2O. A 30% solution of H2O2 is marketed as ‗100V‘ hydrogen peroxide. It means that 1ml of 30% H2O2 solution will give 100V of oxygen at STP. Hydrogen peroxide has a non-planar structure.
CHEMICAL PROPERTIES: It acts as an oxidising as well as reducing agent in both acidic & alkaline media. 1.Oxidising action in acidic medium: 2Fe2+ +2H+ +H2O2 2Fe3+ +2H2O PbS +4H2O2 PbSO4+4H2O 2.Reducing action in acidic medium: 2MnO4- +6H+ +5H2O2 2Mn2+ +8H2O+5O2 HOCl +H2O2 H3O+ +Cl- +O2
STORAGE H2O2 decomposes slowly on exposure to light. 2H2O2 2H2O+O2 In the presence of metal surfaces or traces of alkali, the above reaction is catalysed. It is, therefore stored in wax-lined glass or plastic vessels in dark. It is kept away from dust because dust can induce explosive decomposition of the compound.
USES: It is used as hair bleach & as a mild disinfectant. As an antiseptic it is sold in the market as perhydrol. It is used to manufacture chemicals like sodium perborate & per-carbonate, which are used in high quality detergents. It is used in the synthesis of hydroquinone, tartaric acid & certain food products & pharmaceuticals etc. It is employed in the industries as bleaching agent for textiles, paper pulp, leather, oils, fats etc. It is also used in environmental chemistry.
HEAVY WATER,D2O It is extensively used as a moderator in nuclear reactors & in exchange reactions for the study of reaction mechanisms. It can be prepared by exhaustive electrolysis of water or as a by-product in some fertilizer industries. PHYSICAL PROPERTIES: Molecular mass: 20.0276 g/mol. Melting point: 276.8K. Boiling point: 374.4K.
Cont….. The bottom ice cubes were made with heavy water, which is water that uses deuterium hydrogen (nucleus with an extra neutron) not regular hydrogen which has no neutron.
USES: It is used for the preparation of other deuterium compounds. For e.g. CaC2 + 2D2O C2D2 + Ca(OD)2 SO3 + D2O D2SO4 Al4C3 + 12D2O 3CD4 + 4Al(OD)3
PROJECT HYDROGEN SUMMARY:-1)Hydrogen is the most abundant and simplest elementin the universe.2)Hydrogen has no elasticity.3)Hydrogen is flameable.4)Hydrogen is energy carrier.5)Hydrogen can be cooled and stored as a liquid.6)Atomic hydrogen is highly reactive.7)Nascent hydrogen is very reactive form of hydrogen.
Liquid and compressed hydrogen storage Technically feasible; in use on prototype vehicles Focus is on meeting packaging, mass, and cost targets Both methods fall below energy density goals Unique vehicle architecture and design could enable efficient packaging and extended range Solid state storage Fundamental discovery and intense development necessary “Idea-rich” research environment
PROJECT HELPERS GUIDANCE :- HEENA SHAIKH MADAM 10TH , 11TH TEXTBOOKS. HYDROGEN REFERENCE BOOK (BRITISH LIBIRARY). INTERNET :- GOOGLE,YAHOO ETC. INTERNET :- MAPS , STATITICS , PHOTOS ETC.