1. The study of heat released or required by chemical reactions
THERMOCHEMISTRY
The study of heat released or required by chemical reactions
Fuel is burned to produce energy - combustion (e.g. when fossil fuels are burned)
CH4(g) O2(g) CO2(g) + 2H2O(l) + energy

2. Energy due to position (stored energy)
What is Energy?
Energy
Kinetic energy (EK)
Potential energy (EP)
Energy due to motion
Energy due to position (stored energy)

3. Law of Conservation of Energy: the total energy of the universe is constant and can neither be created nor destroyed; it can only be transformed.

4. Systems & Surroundings
In thermodynamics, the world is divided into a system and its surroundings
A system is the part of the world we want to study (e.g. a reaction mixture in a flask)
The surroundings consist of everything else outside the system
SYSTEM
CLOSED
OPEN
ISOLATED

5. OPEN SYSTEM: can exchange both matter and energy with the surroundings (e.g. open reaction flask, rocket engine)
CLOSED SYSTEM: can exchange only energy with the surroundings (matter remains fixed) e.g. a sealed reaction flask
ISOLATED SYSTEM: can exchange neither energy nor matter with its surroundings (e.g. a thermos flask)

6. e.g. kettle heats on a gas flame
HEAT and WORK
HEAT is the energy that transfers from one object to another when the two things are at different temperatures and in some kind of contact
e.g. kettle heats on a gas flame
cup of tea cools down (loses energy as heat)
Work is the transfer of energy that takes place when an object is moved against an opposing force
Work stimulates uniform motion
Heat and work can be considered as energy in transit

7. UNITS OF ENERGY S.I. unit of energy is the joule (J)
Heat and work ( energy in transit) also measured in joules
1 kJ (kilojoule) = 103 J
Calorie (cal): 1 cal is the energy needed to raise the temperature of 1g of water by 1oC
1 cal = J

8. A change in internal energy can be identified with the heat supplied at constant volume
ENTHALPY (H)
(comes from Greek for “heat inside”)
As most reactions in chemistry take place at constant pressure we can say that:
A change in enthalpy = heat supplied
The heat supplied is equal to the change in another thermodynamic property called enthalpy (H)
i.e. H = q
this relation is only valid at constant pressure

9. All chemical reactions either release or absorb heat
Reaction Enthalpies
All chemical reactions either release or absorb heat
Exothermic reactions:
Reactants products energy as heat (H -ve)
e.g. burning fossil fuels
Endothermic reactions:
Reactants + energy as heat products (H +ve)
e.g. photosynthesis

10. EXOTHERMIC & ENDOTHERMIC REACTIONS
Exothermic process: a change (e.g. a chemical reaction) that releases heat.
A release of heat corresponds to a decrease in enthalpy
Exothermic process: H < 0 (at constant pressure)
Burning fossil fuels is an exothermic reaction
Photosynthesis is an endothermic reaction (requires energy input from sun)
Endothermic process: a change (e.g. a chemical reaction) that requires (or absorbs) heat.
An input of heat corresponds to an increase in enthalpy
Endothermic process: H > 0 (at constant pressure)

11. Measuring Heat
reaction
Exothermic reaction, heat given off & temperature of water rises
reaction
Endothermic reaction, heat taken in & temperature of water drops

12. How do we relate change in temp. to the energy transferred?
Heat capacity (J/oC) = heat supplied (J)
temperature (oC)
Heat Capacity = heat required to raise temp. of an object by 1oC
Specific heat capacity is the quantity of energy required to change the temperature of a 1g sample of something by 1oC
Specific Heat Capacity (C)
Heat (joules or calorie)(q)
Mass (m) x change in Temp (∆ T) =

13. Vaporization Melting Freezing
Energy has to be supplied to a liquid to enable it to overcome forces that hold molecules together
endothermic process (H positive)
Melting
Energy is supplied to a solid to enable it to vibrate more vigorously until molecules can move past each other and flow as a liquid
endothermic process (H positive)
Freezing
Liquid releases energy and allows molecules to settle into a lower energy state and form a solid
exothermic process (H negative)
(we remove heat from water when making ice in freezer)