2.1 Thermochemistry

Enthalpy change of reaction

is the enthalpy change when the molar quantities of reactants, as stated in the balanced equation, react under standard conditions

Enthalpy change of combustion

is the energy released when one mole of a substance burns completely in oxygen under standard conditions.

Enthalpy change of formation

is the enthalpy change when one mole of a compound is formed from its elements, in their standard states, under standard conditions

Bond enthalpy

is the energy required to break one mole of that particular bond in the gaseous state.

Hess’ Law

that the enthalpy change converting reactants to products is the same regardless of the route taken provided the initial and final conditions are the same.

Q=

mcΔT

ΔH =

-Q/n

Exothermic

there is a net transfer of energy from the system to the surroundings.

Endothermic

there is a net transfer of energy from the surroundings to the system.

Sign for exothermic

negative

Sign for endothermic

positive

Exothermic energy level diagram

Endothermic energy level diagram

Specific heat capacity

the energy needed to raise the temperature of 1g of the material by 1K

Standard conditions are

1 mol dm-3 100kPa 298K

Calorimetry

the measurement of energy changes of a system by measuring their effect on surroundings.