1. Thermochemistry: The study of heat changes that occur during chemical reactions and physical changes of state

2. Energy
Heat (q) =
Form of energy
always flows from a warmer object to a cooler object
Law of Conservation of Energy – Energy is neither created nor destroyed

3. Heat (q) The unit is the joule (J) or calorie (cal)
1 calorie = J
1 Calorie (food) = 1000 cal (science) = 1 kcal

4. Specific Heat (C)
Specific Heat (C) – the amount of heat required to raise 1 gram of a substance by 1C
Specific heat is an intensive property,
Every substance has its own specific heat
Ex. Water = 4.18 J/(g ∙ ºC)
Glass = 0.50 J/(g ∙ ºC)

5. Specific Heat
Units for Specific Heat ( C ) = J / g ● ºC (joules per gram degree Celsius)
Equation for Specific Heat: C = q / (m Δ T)
This equation can be rearranged to solve for heat (q)
q= CmΔT
C = specific heat;
q = heat;
m = mass and
ΔT = change in temperature (Tf – Ti)

6. Specific Heat
A 10.0 g sample of iron changes temperature from 25.0C to 50.4 C while releasing 114 joules of heat. Calculate the specific heat of iron.

7. Example
C= q/ (m∆T)
C=114 J/ (10.0 g x 25.4°C)
c = J/g C

8. Another example
If the temperature of 34.4 g of ethanol increases from 25.0 C to 78.8 C how much heat will be absorbed if the specific heat of the ethanol is 2.44 J/g C

9. Another example
First, rearrange the specific heat formula to solve for heat
q = CmT
q = (2.44 J/g°C)(34.4g)(78.8°C – 25.0°C)
q = 4520 J

10. Yet another example
4.50 g of a gold nugget absorbs 276 J of heat. What is the final temperature of the gold if the initial temperature was 25.0 C & the specific heat of the gold is 0.129J/g C

11. Yet another example C= q/ (m∆T); rearrange to find ∆T = q / (C x m)
∆T = 276 J / (.129 J/g°C x 4.50 g)
T = 475C
T = Tf-Ti
475 = Tf - 25
Tf = 500 C

12. Phase Changes
How many joules are required to raise the temperature of g of ice at -10.0˚C to 50.0˚C?
Cice = 20.9 J/g ˚C Cwater = J/g ˚C
ΔHfusion = 6.01 kJ/mol
Answer: kJ

13. How much energy is required to bring 45 g of benzene from - 10˚C to 70˚C?
(hint: draw a heating curve to help)