1. Thermochemistry
The study of the energy changes that accompany physical, chemical or nuclear changes in matter

2. Definitions: recall physics
Energy (E):
The ability to do work; measured in Joules (J)
Work:
Amount of energy applied or transferred over a distance
Potential Energy (Ep):
Energy of object due to its position or composition; stored energy
Kinetic Energy (Ek):
Energy of object due to its motion; movement energy

3. Definitions: recall physics
Thermal Energy (H):
Total quantity of kinetic & potential energy within a substance, Ep + Ek = H
Heat (q):
The transfer of thermal energy from a warm body to cooler body
Temperature:
A measure of the average kinetic energy of particles in a substance/object

4. Definitions: new ones Chemical System: Surroundings: Open System
The group of reactants & products being studied
Surroundings:
The environment in which the chemical reaction takes place; substance that is not part of the reaction
Open System
Matter & Energy able to leave system
Closed System
Energy able to leave system
Isolated System
Neither matter nor energy able to leave system

5. -qsurroundings = +qsystem
Calorimetry
Measuring energy changes in a reaction
q = mcΔT
We measure the ΔT of the surroundings and calculate the thermal energy, q, lost or gained by the surroundings
-qsurroundings = +qsystem

6. q = mcΔT q = thermal energy (or heat) (Joules, J)
m = mass of surroundings (grams, g)
ΔT = Tfinal – Tinitial = change in temperature (oC or K)
c = specific heat capacity;
the energy (in Joules) needed to raise 1 gram of surroundings by 1 degree; (J/g oC ) or kJ/kg oC

7. Specific Heat Capacity,(c);

8. Definitions: new ones Enthalpy (H): another term for thermal energy
Enthalpy Change (ΔH): the change in thermal energy from reactants to products; this equals q under constant pressure:
ΔHsystem = qsystem
ΔHsystem = Hproducts – Hreactants
Where qsurroundings is the measurable quantity
Endothermic:
intake of energy, -qsurroundings & +qsystem & + ΔH
Exothermic:
release of energy, +qsurroundings & -qsystem & - ΔH

9. Molar Enthalpy Change ΔHn:
Molar Enthalpy Change (ΔHn): enthalpy change associated with any change (physical, chemical or nuclear) in one mole of a substance; J/mol or kJ/mol
ΔHrxn = nΔHn

10. Common Molar Enthalpies

11. Example:
Ethanol is used to disinfect skin before receiving a flu shot. How does this feel on your skin? The enthalpy of vaporization (ΔHvap)of ethanol is 38.6 kJ/mol. What is the enthalpy change (ΔHrxn) of this reaction if 1.0g of ethanol is rubbed on your skin?

12. Expressing Molar Enthalpy Changes:
As part of chemical equation:
Associated ΔH value:
Potential Energy Diagram:

13. 3) Potential Energy Diagram: