Energetics Terms

Temperature

Measure of the average kinetic energy of particles

Exothermic reaction

Heat energy is transferred from a system (chemical reaction) to the surroundings - the surroundings get hotter.

Endothermic reaction

A system takes in heat energy from the surroundings - the surroundings get cooler. ΔH is positive.

Standard conditions

100 kPa and 298K

Standard state

The most stable form in which a substance would exist in standard conditions

Standard enthalpy change of combustion

The enthalpy change when one mole of a substance is completely burnt in oxygen under standard conditions.

Enthalpy change of solution

The amount of energy given out/taken in when one mole of solute dissolves in excess solvent.

Standard enthalpy change of formation

The enthalpy change when one mole of the substance is formed from its elements in their standard states under standard conditions.

Average bond enthalpy

The energy required to break one mole of covalent bonds in a gaseous molecule under standard conditions.

First ionisation energy

The enthalpy change when one electron is removed from each atom in one mole of gaseous atoms. (Endothermic)

Second ionization energy

The enthalpy change accompanying the removal of one electron from each ion in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions. (Endothermic)

Enthalpy change of atomisation

The enthalpy change when one mole of gaseous atoms is formed from an element in its standard state. (Endothermic)

First electron affinity

The enthalpy change when one electron is added to each atom in one mole of gaseous atoms. (Exothermic)

Second electron affinity

Enthalpy change when each atom in one mole of gaseous 1- ions gains an electron to form one mole of gaseous 2- ion. (Endothermic)

Lattice enthalpy

The enthalpy change when one mole of ionic compound is broken apart into its constituent gaseous ions. (Endothermic)

Hydration enthalpy

Enthalpy change when one mole of gaseous ions are surrounded by water molecules to form an infinitely dilute solution. (Exothermic)

Enthalpy change of solution

Enthalpy change when one mole of solute is dissolved in excess solvent to form a solution of infinite dilution. (Endothermic/Exothermic)

Entropy

A measure of disorder- how the available energy is distributed among the particles.

Spontaneous reaction

One that occurs without any outside influence, where Gibbs free energy is <0

Enthalpy of neutralisation

Enthalpy change that occurs when one mole of water is formed from a reaction between an acid and an alkali (always exothermic)