1. Thermochemistry

2. Thermochemistry: Study of energy changes that occur during chemical reactions and changes in state
Chemical Potential Energy: Energy stored in chemical bonds of a substance

3. What is heat, how does it flow?
Heat (q) : energy transferred from one object to another due to temperature difference
Heat always flows from warmer object to cooler object!
Why?
Hint – Energy…

4. Energy
Law of conservation of energy: Energy is not created or destroyed
Endothermic Process: absorbs heat from the surroundings
Reactants + Heat  Products
Exothermic Process: releases heat to surroundings
Reactants  Products + Heat

5. 1 Calorie = 1 kilocalorie = 1000 calories
Units for Heat
calorie: heat needed to raise 1.0 gram of water 1.0ᵒC
1 Calorie = 1 kilocalorie = 1000 calories
Ex. Kudos Bar 130 Calories = kcal = 130,000 calories
Joule – SI unit for energy
1 J = cal J = 1 cal
How many joules are in a Kudos bar?

6. Specific Heat
Specific Heat: Amount of heat needed to increase the temperature of 1g of a substance exactly 1ᵒC.
specific heat (C) = Heat (Joules or calories)
Mass (grams) x change in temperature (C)
C = q
( m ) (T)

7. The temperature of a 95. 4g piece of copper increases from 25
The temperature of a 95.4g piece of copper increases from 25.0ᵒC to 48.0ᵒC when the copper absorbs 849J of heat. What is the specific heat of copper?

8. T = change in the temperature
Calorimetry
Calorimetry: measure of heat flow into or out of a system
Enthalpy (H): the internal energy of the molecules of a material
Heat(q) = H = m (C) T
H = change in the heat
m = mass
C = specific heat
T = change in the temperature

9. Thermochemical Equations
Enthalpy change (ΔH) can be written as a product or a reactant.
Endothermic
2NaHCO3(s) +129kJ  Na2CO3(s) + H2O(g) + CO2 (g)
2NaHCO3(s)  Na2CO3(s) + H2O(g) + CO2 (g) ΔH=129kJ
Exothermic
CaO(s) + H2O(l)  Ca(OH)2(s) kJ
CaO(s) + H2O(l)  Ca(OH)2(s) ΔH=-65.2kJ

10. 2NaHCO3(s) + 129kJ  Na2CO3(s) + H2O(g) + CO2(g) ΔH=129kJ How much heat (in kJ) is required to decompose 2.24mol of NaHCO3? ΔH = 2.24mol NaHCO3 x 129kJ 2mol NaHCO3 = 144kJ

11. C2H5OH(l) + 3O2(g)  2CO2(g) + 3H2O(l) ΔH=-1368kJ
How much heat (in kJ) is released when 12.5g of ethanol burns?

12. Fusion and Solidification
Molar Heat of Fusion (ΔHfus): heat absorbed by 1 mol of a substances as it melts (solid  liquid)
ENDOTHERMIC
solid + heat  liquid
Molar Heat of Solidification (ΔHsolid): heat lost when 1 mol of a liquid solidifies (liquid  solid)
EXOTHERMIC
liquid  solid + heat
ΔHfus = -ΔHsolid

13. Vaporization and Condensation
Molar Heat of Vaporization (ΔHvap): amount of heat needed to convert 1 mol of liquid to gas (liquid  gas)
ENDOTHERMIC
liquid + heat  gas
Molar Heat of Condensation: (ΔHcond): amount of heat released when 1 mol of vapor condenses (gas  liquid)
EXOTHERMIC
gas  liquid + heat
ΔHvap = -ΔHcond

14. H2O(s)  H2O(l) ΔHfus = 6.01kJ/mol How many grams of ice at 0ᵒC will melt if 2.25kJ of heat are added?