AP Chem- Thermochemistry Unit

Calorimetry

Measures heat of reaction

Heat from rxn that warms up water

q(water) = (water mass)(Cp)(DeltaT)

Heat from rxn warms “bomb”

q(bomb) = (heat capacity)(DeltaT)

-q(rxn) =

q(bomb) + q(water)

ΔH

Change in heat content of a system

q = ΔH

As long as pressure stays constant

ΔH =

Hfinal - Hinitial

-ΔH

Heat lost in rxn (exothermic)

+ΔH

Heat gained in rxn (endothermic)

State functions

Pathways from which you get from point a to point b don’t matter

Thermochemistry

Science of Energy Transfer as heat

Delta T

Measures Energy transfer

Thermodynamics depends on

Law of conservation of energy

Law of Conservation of Energy

The total energy of an isolated system remains constant but conserved over time.

Directionality of energy transfer

Energy transfer of heat is always from a hotter to a cooler object

1 Cal

4.184 Joules

ΔH

Enthalpy change

Enthalpy

The total heat content of a system under constant pressure

Ea

Activation energy

Heat Capacity

Amount of energy required to raise an object’s (size) temperature by 1 C

Specific heat capacity

Amount of energy required to raise a material’s (compound) temperature by 1 C

q

Heat lost or gained

Heat transfer equation

q = m*Cp*DeltaT

Heat (q) is related to:

Sample mass, Change in T, and Specific heat capacity (Cp)

0 C

Melting/ freezing point

100 C

Boiling/ condensation

ΔH fusion

335 J/ g

ΔH vapor

2330 J/ g

ΔH fusion is

Heat required to convert a solid at its melting point (0 C)

ΔH vapor

Heat required to convert a liquid at its boiling point (100 C)

Activated complex

Midway between reaction

Cp H20

4.184 J/ gC

Hess’s Law

If a reaction is the sum of other reactions, then the total enthalpy is the sum of the other enthalpies