1. Thermochemistry
Chapter 16

2. Vocabulary
Thermochemistry: the study of the transfers of energy as heat that accompany chemical reactions and physical changes
Calorimeter: a device used to measure the energy as heat absorbed or released in a chemical or physical change

3. More Vocabulary
Temperature: a measure of the average kinetic energy of the particles in a sample of matter
Joule: the SI unit of heat as well as all other forms of energy, “J”
Heat: the energy transferred between samples of matter because of a difference in their temperatures

5. Specific Heat
Specific heat: the amount of energy required to raise the temperature of one gram of a substance by one Celsius degree (or one kelvin)
Units are J/(g °C) or J/(g K)
Usually measured under constant pressure

6. More about Specific Heat
Symbol for specific heat is cp
“q” represents energy lost or gained
“m” is the mass of the sample
“ΔT” is the difference between the initial and final temperatures
or q = cp  m  ΔT

7. Problem
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 as heat.
What is the specific heat of this type of glass?
How much energy will the same glass sample gain when it is heated from 314 K to 344 K?
0.20 J/gK
Practice problems 1-2 on page 535 in school textbook
24 J

8. Enthalpy of Reaction “H” is the symbol for enthalpy
Enthalpy is measured as a change
“ΔH” is the symbol for the energy absorbed as heat during a chemical reaction at constant pressure
Enthalpy change: the amount of energy released or absorbed by a system as heat during a process at constant pressure

9. Enthalpy of Reaction
Enthalpy of reaction: the quantity of energy transferred as heat during a chemical reaction
Enthalpy change for a reaction is calculated with the following:
ΔH = Hproducts – Hreactants
Is the difference between the stored energy of the reactants and products

10. Thermochemical Equation
Thermochemical equation: an equation that includes the quantity of energy released or absorbed as heat during the reaction
The coefficients are numbers of moles, never molecules (so can be a fraction)

11. Exothermic Reaction
Thermochemical equations are usually written by designating the value of ΔH
ΔH = kJ
Sometimes they are written showing the energy as a product or reactant

13. Endothermic Reaction Energy is absorbed for the reaction to occur
ΔH = kJ
Written with energy as a reactant:

15. Entropy
Entropy: a measure of the degree of randomness of the particles, such as molecules, in a system
Is given the symbol “S”
Compare a solid and a gas at the same temperature; the gas has greater entropy because its particles are moving rapidly in all directions