1. Chapter 17
Thermochemistry

2. Thermochemistry
The study of energy changes that occur during chemical reactions and changes in state.

3. Thermochemistry
Energy: the ability to do work or to supply heat
ENERGY (Joule or calorie) = HEAT (J or cal)
1 cal = 4.18 J
Chemical Potential Energy: stored energy in
chemicals

4. Heat and temperature are concepts that are often confused
Heat vs. Temp.
Heat and temperature are concepts that are often confused

5. Heat vs. Temp.
Amount of energy in a system
Degree of hotness or coldness of an object
Form of energy
Measures the average kinetic energy of molecules
Flows from a warmer object to a cooler one
It is measured in Joules or calories
It is measured in degrees

6. Calorie vs. calorie
Calorie = refers to food (dietary)
Calorie = 1kilocalorie = 1,000 calories
Snickers Bar = 280 Calories = 280 kilocalories
= 280,000 calories
calorie= a unit of heat

7. Specific Heat Capacity
The amount of heat it takes to raise the temperature of 1 g of a substance 1oC
q =m ΔT Cp
q =heat energy (J or cal)
m =mass (g)
ΔT =(Tf – Ti) = oC
Cp = specific heat =
J = heat (J)
g x oC mass (g) x (Tf – Ti)

8. Q =m Δ T Cp
q = g oC J
g x oC
When units are canceled, q = Joules

9. Specific Heat Capacity
The amount of heat it takes to raise the temperature of 1 g of a substance 1oC
For example: WATER VS. METAL
-Higher the specific heat: the less fluctuation of
heat and therefore the less fluctuation of the
temp. of the object.
Water
Iron
4.18 J/(g x oC)
0.46 J/(g x oC)
High
Low

10. Exothermic vs. Endothermic
Exothermic: a process in which heat is released to the surrounding
The system loses heat as the surroundings heat up
q has a negative value because the system is losing heat
Endothermic: a process in which the system gains heat as the surroundings cool down
Heat flows into a system
q has a positive value because the system is gaining heat

11. Calorimetry
To measure specific heat capacity a bomb calorimeter is used.
Calorimetry is based on the principle:
Law of conservation of energy

12. Bomb Calorimeter

13. Plastic Cup Calorimeter