1. Thermodynamics

2. What is thermochemistry?
The study of the changes in heat energy that accompany chemical reactions and physical changes

3. How do we measure these changes in heat energy?
Both physical and chemical processes should be conducted in a calorimeter, a device used to measure the heat absorbed or released
Calorimeters should have good isolative properties to prevent heat from entering or leaving when measuring the heat transfer of the physical or chemical process

4. What types of heat transfer will we measure?
Endothermic --> when heat is absorbed during a chemical or physical change
Examples include:
fusion (melting) solid + ΔH  liquid
sublimation solid + ΔH  gas (dry ice)
vaporization liquid + ΔH gas
baking bread
photosynthesis

5. Exothermic-->when heat is released during a chemical or physical change
Examples include:
Solidification (freezing) liquid  solid + ΔH
Condensation gas  liquid + ΔH
Deposition gas  solid + ΔH (frost)
Rusting iron
Burning a candle

6. Mathematical equation used to measure energy absorbed or released during a temperature change
Q = cpn∆T
Q = energy gained or lost
Cp = specific heat
n = amount (g)
∆T = change in temperature

7. How will this energy be measured?
The SI unit of energy is the Joule (J)
The calorie(cal) is more commonly used to measure food energy
1 cal = 4.18 J

8. What is specific heat (cp)?
The amount of heat energy required to raise the temperature of 1 gram of a substance by 1 Celsius degree or Kelvin
This value is dependant on:
-the substance
-the state the substance is in (solid, liquid or gas)

9. Mathematical equation used to measure energy absorbed or released during a phase change
Q = Hxn
Q = energy gained or lost
Hx = heat of fusion, vaporization, solidification or condensation
n = amount (grams or moles)

10. What is Hx?
Heat of fusion (Hf) --> the amount of energy required to melt 1 mole (or gram depending on the units given) at it’s melting point
Heat of solidification (Hs) --> same as Hf except a negative value because energy needs to be removed to go from a liquid to a solid

11. Heat of vaporization (Hv) --> the amount of energy required to vaporize 1 mole (or gram) at it’s boiling point
Heat of condensation (Hc) --> same as Hv except a negative value because energy needs to be removed to go from a gas to a liquid

12. Endo Versus Exo?
An endothermic energy change will be denoted with a positive value
Ex. 468 J
An exothermic energy change will be denoted with a negative value
Ex cal

13. Simple Practice Problems
How many joules of heat are given off when 5.0 g of water cool from 75.0°C to 25.0°C? (cp= 4.18 J/g°C)
How many calories is this?

14. How many joules of energy does it take to melt 35 g of ice at 0°C?
(Hf = 333 J/g)

15. How many calories are given off when 85 g of steam condenses to liquid water? (Hv= 539.4 cal/g)

16. Practice Problem
An unknown compound has the following properties:
Hs = J/mol
Hv = J/mol
cp (liquid) = J/mol•C
cp (gas) = 42.9 J/mol •C
mp = 5C
bp = 15C
A. Be able to sketch a fp/bp graph for this substance, labeling the axes and indicating the mp and bp)
B. Suppose J of heat are added to a 1.08 mol solid sample of this substance at 5C. When all the heat is absorbed by the substance, at what temperature and state(s) will the substance be?

17. 1 cal = 4.18 J

18. What is Equilibrium?
A dynamic condition in which 2 opposing changes occur at equal rates in a closed system.
Ex. A pool is at maximum capacity with 50 people and at equilibrium. If 2 people enter the pool, how many people need to exit the pool to keep it at equilibrium?