1. Ch.17: Reaction Energy and Reaction Kinetics
Introduction to Thermochemistry

2. Introduction Thermochemistry: Temperature: (T)
study of transfers of energy as heat occurring during chemical and physical changes
Temperature: (T)
average kinetic energy of the particles in a sample
as kinetic energy increases, so does temperature

3. Heat
(q) energy transferred between samples because of their difference in T
moves spontaneously from matter with higher T to matter with lower T
heat can’t be measured directly so T is used to track transfer of heat
amount of energy transferred is measured in Joules (J)

4. Heat Transfer

5. Heat
measured using a calorimeter (reaction container that is surrounded by water)
the energy given off during a reaction is equal to the energy absorbed by the water

6. Two Types of Calorimeters

7. Specific Heat
the amount of energy transferred during a temperature change depends on:
type of material
mass of material
size of T change
specific heat: (cp) the amount of energy required to raise the T of one gram of substance by one °C

8. Specific Heat
measured under constant pressure

9. Why does water have such a high specific heat?
water metal
Water molecules form strong bonds with each other; therefore it takes more heat energy to break them.
Metals have weak bonds and do not need as much energy to break them.

10. Example
A 4.0 g sample of glass was heated from 274 K to 314 K and was found to have absorbed 32 J of energy.
Find the specific heat of the glass sample.

11. Example
How much energy will the same glass sample gain when heated from 314 K to 344 K?

12. Example
If 200. g of water at 20°C absorbs 41,840 J of heat, what will its final T be? The specific heat of water is J/g°C.

13. Example
Aluminum has a specific heat of J/g°C and water has a specific heat of 4.18 J/g°C. How high must the temperature of the aluminum be to cause the water temperature to raise from 22°C to 28°C? You are using 25 g of aluminum and 50. grams of water.
T = 84°C