1. Thermochemistry
Thermochemistry the study of the energy changes that accompany physical or chemical changes in matter.
Changes may be classified as physical, chemical, or nuclear
Examples:
Ice melting
Iron rusting
An isotope used in medical therapy undergoes radioactive decay

2. Heat energy and Changes
When discussing the transfer of heat energy, it is important to distinguish between the substances undergoing a change (chemical systems) and the system’s environment (surroundings)
Chemical System:
A set of reactants and products under study, usually represented by a chemical equation
Surroundings:
All matter around the system that is capable of absorbing or releasing thermal energy.

3. Heat and Energy Changes
The above is an equation for burning ethyne
The surroundings in this reaction would include anything that could absorb the thermal energy that has been released
When the reaction occurs, heat energy (q) is transferred between substances
ie. metal parts, the air, and the welder’s protective clothing
When heat transfers between a system and its surroundings, measurements of the temperature of the surroundings are used to classify the change as exothermic or endothermic

4. Heat &Temperature Heat energy (q):
measure of the total kinetic energy in an object
(and so depends on how large the object is, or how much of it there is)
The amount of energy transferred between substances
it is represented by the symbol q with units of Joules (J)
Temperature:
Measure of the Average kinetic energy of the particles in a sample of matter
measured most often in (oC, K)

5. Exothermic & Endothermic Reactions
Exothermic reaction
Releasing thermal energy as heat flows out of the system
Kinetic energy of the surrounding molecules increases  temperature increases
Endothermic reaction
Absorbing thermal energy as heat flows into the system
Kinetic energy of the surrounding molecules decreases  temperature decreases

6. Endothermic reactions
Endothermic reactions absorb thermal energy, and so cause a decrease in temperature
Examples:
Both examples above are endothermic since
heat flows into the system in order for the reaction to occur

7. Exothermic reactions
Exothermic reactions release heat energy to their surroundings
They cause the temperature
of the surrounding to increase
Examples
Combustion
Neutralization
Reactions of metals with water

8. Exothermic Reactions
This combustion reaction is exothermic because heat flows into the surroundings
Notice the heat energy is being produced by the reaction, & transferred to the surroundings
Once heat is transferred to the surroundings, it is used to increase the thermal energy of the molecules in the surroundings
Molecules in the surroundings have greater kinetic energy, the temperature of the surroundings will increase.

10. Calorimetry Calorimetry: the study of heat flow and heat measurement
A calorimeter is a device used to make this measurement
Calorimetry experiments determine heats of reaction (enthalpy changes, or H) by measuring temperature changes produced in a calorimeter
bomb calorimeter
used to find heat of combustion.
The “bomb” contains oxygen
and a sample of the material
burned
Styrofoam cup calorimeter

11. Measuring Energy Changes
The amount of heat energy given by a substance will depend on:
Mass (in grams)
Temperature Change (T)
Type of Substance
These factors can be combined into an equation to represent the quantity of heat (q) transferred…

12. The Quantity of Heat energy
q = quantity of heat energy transferred
m = mass (g)
T = Temperature change
c = the specific heat capacity

13. Important Properties: Heat Capacity and Specific Heat Capacity= q mc D T?
How did we arrive at
Important Properties: Heat Capacity and Specific Heat Capacity
The thermal properties of a substance are those that describe its ability to absorb or release heat without changing chemically
They include heat capacity and specific heat capacity.

14. Heat Capacity
The heat capacity of an object is the amount of heat needed to raise its temperature by 1C
Heat Capacity = Heat absorbed (1) T
ex: The heat capacity of a cup of water at 18C is the # of joules of energy needed to raise its temperature to 19C

15. Ex. 1: Calculating Quantity of Heat
What would the final temperature be if J of heat were transferred into 10.0 g of methanol initially at 20 0C ?

16. Calculating Quantity of Heat
Q2 When 600 mL of water in an electric kettle is heated from 20 0C to 85 0C to make a cup of tea, how much heat flows into the water?
Q3 Calculate the heat absorbed by 250 ml of water to raise its temperature from C to C. The specific heat capacity of water is 4.18 J/(g·0C)
Q4 Iron metal has a specific heat capacity of J/(g·0C). How much heat is transferred to a 5.0 g piece of iron, initially at C, when it is placed in a pot of boiling water? The final temperature of the metal is 100 0C.