This document provides an overview of exothermic and endothermic reactions, calorimetry, and how to calculate enthalpy changes. The key points are:
- Exothermic reactions release heat while endothermic reactions absorb heat.
- Enthalpy change (ΔH) is the quantity of heat released or absorbed during a chemical reaction.
- Calorimetry experiments allow calculation of ΔH by measuring the temperature change of a reaction mixture.
- Sample problems demonstrate how to use calorimetry data like mass changes and temperature differences to calculate the enthalpy change for a reaction.
Carbon belongs to the group IV of the periodic table.
It has four electrons in its outermost orbit, so its valency is four.
Carbon is a non-metal.
Why so many Carbon Compounds in nature
Because carbon is chemically unique.
Only carbon atoms have the ability to combine with themselves to form long chains
The number of carbon compounds is larger than that of all other elements put together.
Occurrence of carbon
The name ‘carbon’ is derived from the Latin
word ‘carbo’ meaning coal. Carbon is found in
nature in free as well as compound state. Carbon in
the free state is found as diamond and graphite, and
in the combined state in the following compounds.
1. As carbon dioxide and in the form of carbonates
such as calcium carbonate, marble, calamine
(ZnCO3)
2. Fossil fuel – coal, petroleum, natural gas
3. Carbonaceous nutrients – carbohydrates,
proteins, fats
4. Natural fibres – cotton, wool, silk
Properties of carbon
Allotropic nature of Carbon
Allotropy - Some elements occur in nature in more than one form. The chemical properties
of these different forms are the same but their physical properties are different. This
property of elements is called allotropy. Like carbon, sulphur and phosphorus also exhibit
allotropy.
Allotropes of carbon
A. Crystalline forms
1. A crystalline form has a regular and definite arrangement of atoms.
2. They have high melting points and boiling points.
3. A crystalline form has a definite geometrical shape, sharp edges and plane surfaces.
This is a summary of the topic "Energy changes" in the GCE O levels subject: Chemistry. Students taking either the combined science (chemistry/physics) or pure chemistry will find this useful. These slides are prepared according to the learning outcomes required by the examinations board.
[ Visit http://www.wewwchemistry.com ] This is a summary presentation of the introductory topics in Organic Chemistry, prepared according to the Singapore-Cambridge GCE A Level 9647 H2 Chemistry syllabus.
Introduction
Discovery of Sub-atomic Particles
Atomic Models
Developments leading to Bohr’s Model of atom
Bohr’s Model for Hydrogen atom
Quantum Mechanical Model of the atoms
Carbon belongs to the group IV of the periodic table.
It has four electrons in its outermost orbit, so its valency is four.
Carbon is a non-metal.
Why so many Carbon Compounds in nature
Because carbon is chemically unique.
Only carbon atoms have the ability to combine with themselves to form long chains
The number of carbon compounds is larger than that of all other elements put together.
Occurrence of carbon
The name ‘carbon’ is derived from the Latin
word ‘carbo’ meaning coal. Carbon is found in
nature in free as well as compound state. Carbon in
the free state is found as diamond and graphite, and
in the combined state in the following compounds.
1. As carbon dioxide and in the form of carbonates
such as calcium carbonate, marble, calamine
(ZnCO3)
2. Fossil fuel – coal, petroleum, natural gas
3. Carbonaceous nutrients – carbohydrates,
proteins, fats
4. Natural fibres – cotton, wool, silk
Properties of carbon
Allotropic nature of Carbon
Allotropy - Some elements occur in nature in more than one form. The chemical properties
of these different forms are the same but their physical properties are different. This
property of elements is called allotropy. Like carbon, sulphur and phosphorus also exhibit
allotropy.
Allotropes of carbon
A. Crystalline forms
1. A crystalline form has a regular and definite arrangement of atoms.
2. They have high melting points and boiling points.
3. A crystalline form has a definite geometrical shape, sharp edges and plane surfaces.
This is a summary of the topic "Energy changes" in the GCE O levels subject: Chemistry. Students taking either the combined science (chemistry/physics) or pure chemistry will find this useful. These slides are prepared according to the learning outcomes required by the examinations board.
[ Visit http://www.wewwchemistry.com ] This is a summary presentation of the introductory topics in Organic Chemistry, prepared according to the Singapore-Cambridge GCE A Level 9647 H2 Chemistry syllabus.
Introduction
Discovery of Sub-atomic Particles
Atomic Models
Developments leading to Bohr’s Model of atom
Bohr’s Model for Hydrogen atom
Quantum Mechanical Model of the atoms
Lecture materials for the Introductory Chemistry course for Forensic Scientists, University of Lincoln, UK. See http://forensicchemistry.lincoln.ac.uk/ for more details.
The chemical energy of a system is changed as a result of a reaction. Calorimetry. Heat of combustion . Calculation of caloric content of sucrose or food. Combustion reaction.
How to Make a Field invisible in Odoo 17Celine George
It is possible to hide or invisible some fields in odoo. Commonly using “invisible” attribute in the field definition to invisible the fields. This slide will show how to make a field invisible in odoo 17.
Unit 8 - Information and Communication Technology (Paper I).pdfThiyagu K
This slides describes the basic concepts of ICT, basics of Email, Emerging Technology and Digital Initiatives in Education. This presentations aligns with the UGC Paper I syllabus.
The Roman Empire A Historical Colossus.pdfkaushalkr1407
The Roman Empire, a vast and enduring power, stands as one of history's most remarkable civilizations, leaving an indelible imprint on the world. It emerged from the Roman Republic, transitioning into an imperial powerhouse under the leadership of Augustus Caesar in 27 BCE. This transformation marked the beginning of an era defined by unprecedented territorial expansion, architectural marvels, and profound cultural influence.
The empire's roots lie in the city of Rome, founded, according to legend, by Romulus in 753 BCE. Over centuries, Rome evolved from a small settlement to a formidable republic, characterized by a complex political system with elected officials and checks on power. However, internal strife, class conflicts, and military ambitions paved the way for the end of the Republic. Julius Caesar’s dictatorship and subsequent assassination in 44 BCE created a power vacuum, leading to a civil war. Octavian, later Augustus, emerged victorious, heralding the Roman Empire’s birth.
Under Augustus, the empire experienced the Pax Romana, a 200-year period of relative peace and stability. Augustus reformed the military, established efficient administrative systems, and initiated grand construction projects. The empire's borders expanded, encompassing territories from Britain to Egypt and from Spain to the Euphrates. Roman legions, renowned for their discipline and engineering prowess, secured and maintained these vast territories, building roads, fortifications, and cities that facilitated control and integration.
The Roman Empire’s society was hierarchical, with a rigid class system. At the top were the patricians, wealthy elites who held significant political power. Below them were the plebeians, free citizens with limited political influence, and the vast numbers of slaves who formed the backbone of the economy. The family unit was central, governed by the paterfamilias, the male head who held absolute authority.
Culturally, the Romans were eclectic, absorbing and adapting elements from the civilizations they encountered, particularly the Greeks. Roman art, literature, and philosophy reflected this synthesis, creating a rich cultural tapestry. Latin, the Roman language, became the lingua franca of the Western world, influencing numerous modern languages.
Roman architecture and engineering achievements were monumental. They perfected the arch, vault, and dome, constructing enduring structures like the Colosseum, Pantheon, and aqueducts. These engineering marvels not only showcased Roman ingenuity but also served practical purposes, from public entertainment to water supply.
Palestine last event orientationfvgnh .pptxRaedMohamed3
An EFL lesson about the current events in Palestine. It is intended to be for intermediate students who wish to increase their listening skills through a short lesson in power point.
Operation “Blue Star” is the only event in the history of Independent India where the state went into war with its own people. Even after about 40 years it is not clear if it was culmination of states anger over people of the region, a political game of power or start of dictatorial chapter in the democratic setup.
The people of Punjab felt alienated from main stream due to denial of their just demands during a long democratic struggle since independence. As it happen all over the word, it led to militant struggle with great loss of lives of military, police and civilian personnel. Killing of Indira Gandhi and massacre of innocent Sikhs in Delhi and other India cities was also associated with this movement.
2. Great thanks to
JONATHAN HOPTON & KNOCKHARDY PUBLISHING
www.knockhardy.org.uk/sci.htm
Much taken from
ENTHALPY
CHANGES
3. Background and Review
First Law of Thermodynamics (Law of Energy Conservation)
Energy can be neither created nor destroyed but it can be converted from one
form to another
Energy Changes in Chemical Reactions
All chemical reactions are accompanied by some form of energy change
Exothermic Energy is given out
Endothermic Energy is absorbed
Examples Exothermic combustion reactions
neutralization (acid + base)
Endothermic photosynthesis
thermal decomposition of calcium carbonate
4. The heat content of a chemical system is called
enthalpy (represented by H).
Key Concept
We cannot measure enthalpy directly, only
the change in enthalpy ∆H i.e. the amount of
heat released or absorbed when a chemical
reaction occurs at constant pressure.
∆H = H(products) – H(reactants)
∆Ho (the STANDARD enthalpy of reaction) is the
value measured when temperature is 298 K and
pressure is 100.0 kPa.
5. If ∆H is negative, H(products) < H(reactants)
There is an enthalpy decrease and heat is
released to the surroundings.
Enthalpy Diagram -Exothermic Change
enthalpy
6. If ∆H is positive, H(products) > H(reactants)
There is an enthalpy increase and heat is
absorbed from the surroundings.
Enthalpy Diagram - Endothermic Change
enthalpy
7. Exothermic reactions release heat
Example: Enthalpy change in a chemical reaction
N2(g) + 3H2(g) 2 NH3(g)
∆H = -92.4 kJ/mol
The coefficients in the
balanced equation
represent the number of
moles of reactants and
products.
8. N2(g) + 3H2(g) 2 NH3(g)
∆H = -92.4 kJ/mol
State symbols are ESSENTIAL as changes of state
involve changes in thermal energy.
The enthalpy change is directly proportional to the
number of moles of substance involved in the reaction.
For the above equation, 92.4 kJ is released
- for each mole of N2 reacted
- for every 3 moles of H2 reacted
- for every 2 moles of NH3 produced.
9. The reverse reaction
2 NH3(g) N2(g) + 3H2(g)
∆H = +92.4 kJ/mol
Note: the enthalpy
change can be read
directly from the
enthalpy profile diagram.
10. Thermochemical Standard Conditions
The ∆H value for a given reaction will depend
on reaction conditions.
Values for enthalpy changes are standardized :
for the standard enthalpy ∆Ho
-Temperature is 298 K
- Pressure is 100 kPa
- All solutions involved are 1 M concentration
11. Calorimetry – Part 1
Specific Heat Capacity
The specific heat capacity of a substance is a physical
property. It is defined as the amount of heat (Joules)
required to change the temperature (oC or K) of a unit
mass (g or kg) of substance by ONE degree.
Specific heat capacity (SHC) is measured in
J g-1 K-1 or kJ kg-1 K-1 (chemistry)
J kg-1 K-1 (physics)
12. Calorimetry – continued
Heat and temperature change
Knowing the SHC is useful in thermal chemistry. Heat
added or lost can be determined by measuring
temperature change of a known substance (water).
Q = mc∆T
heat = mass x SHC x ∆Temp
13. Calorimetry – Part 2
Applications
A calorimeter is used to
measure the heat
absorbed or released in
a chemical (or other)
process by measuring
the temperature change
of an insulated mass of
water.
14. Sample Problem 1
When 3 g of sodium carbonate are added to 50 cm3 of
1.0 M HCl, the temperature rises from 22.0 °C to 28.5 °C.
Calculate the heat required for this temperature change.
15. Sample problem 2: 50.0 cm
3
of a 1.00 mol dm
-3
HCl solution is mixed with 25.0
cm
3
of 2.00 mol dm
-3
NaOH. A neutralization reaction occurs. The initial
temperature of both solutions was 26.7
o
C. After stirring and accounting for
heat loss, the highest temperature reached was 33.5
o
C. Calculate the enthalpy
change for this reaction.
NaOH HCl
both 26.7o
.
26.7o 33.5o
16. After writing a balanced equation, the molar quantities and
limiting reactant needs to be determined.
Note that in this example there is exactly the right amount of
each reactant. If one reactant is present in excess, the heat
evolved will associated with the mole amount of limiting reactant.
Sample problem 2: 50.0 cm
3
of a 1.00 mol dm
-3
HCl solution is mixed with 25.0
cm
3
of 2.00 mol dm
-3
NaOH. A neutralization reaction occurs. The initial
temperature of both solutions was 26.7
o
C. After stirring and accounting for
heat loss, the highest temperature reached was 33.5
o
C. Calculate the enthalpy
change for this reaction.
17. Next step – determine how much heat was released.
There are some assumptions in this calculation
- Density of reaction mixture (to determine mass)
- SHC of reaction mixture (to calculate Q)
Sample problem 2: 50.0 cm
3
of a 1.00 mol dm
-3
HCl solution is mixed with 25.0
cm
3
of 2.00 mol dm
-3
NaOH. A neutralization reaction occurs. The initial
temperature of both solutions was 26.7
o
C. After stirring and accounting for
heat loss, the highest temperature reached was 33.5
o
C. Calculate the enthalpy
change for this reaction.
18. Final step – calculate ΔH for the reaction
Sample problem 2: 50.0 cm
3
of a 1.00 mol dm
-3
HCl solution is mixed with 25.0
cm
3
of 2.00 mol dm
-3
NaOH. A neutralization reaction occurs. The initial
temperature of both solutions was 26.7
o
C. After stirring and accounting for
heat loss, the highest temperature reached was 33.5
o
C. Calculate the enthalpy
change for this reaction.
19. Sample problem 3: to determine the enthalpy of combustion for ethanol (see
reaction), a calorimeter setup (below) was used. The burner was lit and allowed
to heat the water for 60 s. The change in mass of the burner was 0.518 g and
the temperature increase was measured to be 9.90
o
C.
What is the big
assumption made
with this type of
experiment?
20. First step – calculate heat evolved using calorimetry
Last step – determine ΔH for the reaction
Sample problem 3: to determine the enthalpy of combustion for ethanol (see
reaction), a calorimeter setup (below) was used. The burner was lit and allowed
to heat the water for 60 s. The change in mass of the burner was 0.518 g and
the temperature increase was measured to be 9.90
o
C.
21. Sample problem 4: 100.0 cm
3
of 0.100 mol dm
-3
copper II sulphate solution is
placed in a styrofoam cup. 1.30 g of powdered zinc is added and a single
replacement reaction occurs. The temperature of the solution over time is
shown in the graph below. Determine the enthalpy value for this reaction.
First step
Make sure you understand
the graph.
Extrapolate to determine
the change in
temperature.
The extrapolation is necessary to compensate for heat loss while the reaction
is occurring. Why would powdered zinc be used?
22. Determine the limiting reactant
Calculate Q
Calculate the enthalpy for the reaction.
Review Exercise 2
Sample problem 4: 100.0 cm
3
of 0.100 mol dm
-3
copper II sulphate solution is
placed in a styrofoam cup. 1.30 g of powdered zinc is added and a single
replacement reaction occurs. The temperature of the solution over time is
shown in the graph below. Determine the enthalpy value for this reaction.