REACTIVITY 1 - CHEMISTRY HL

Enthalpy ΔH

Measure of chemical potential energy stored in a system

Heat

A form of energy transfer occuring as a result of a temperature difference

Temperature

Measure of average kinetic energy

Exothermic reaction

A reaction that gives out (releases) heat, causing the enthalpy to decrease (ΔH < 0)

Products < Reactants

Activation energy E_a

Minimum energy required to react

Standard enthalpy change ΔH⦵ codintions

• 100 kPa (~1 atm)

• 1 moldm^-3 for all reactants

• Standard states

bond enthalpy

Energy needed to break one mole of bonds in gaseous molecules under standard conditions.

Hess’s Law

Enthalpy change for a reaction is indpendent of the pathway between its initial and final states. (provided the starting conditions and final conditions, and reactants and products, are the same.)

Standard enthalpy change of combustion ΔH_c⦵

Enthalpy change that occurs when one mole of the substance burns completely under standard conditions.

Standard enthalpy change of formation ΔH_f⦵

Enthalpy change that occurs when one mole of the substance is formed from its elements in their standard states.

• 298K

• 1.00×10^5 Pa

The first ionization energy ΔH_i⦵

Energy needed to form the positive ion from a gaseous atom. (endothermic)

The first electron affinity ΔH_e⦵

Enthalpy change when one mole of gaseous atoms attracts one mole of electrons.