Chemistry Definitions

Standard enthalpy of reaction

The enthalpy change when the amounts of reactants in a specified stochiometric equation react together under standard conditions of 298 K and 100 kPa with all compounds in their standard states and solutions at a concentration of 1.00 mol dm−3

Born-Haber cycle

The energy cycle used for determining the lattice enthalpy of an ionic compound

Lattice enthalpy

The energy it takes for form gaseous ions from one mole of solid ionic compound

Electron affinity (EA)

The energy released when one mole of electrons is added to one mole of gaseous atoms

Bond energy (E)

The energy required to break one mole of bonds in the gaseous state.

Enthalpy of atomisation (ΔH⦵atom)

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

Ionisation energy (IE)

The energy required to remove one mole of electrons from one mole of gaseous atoms

Electronegativity

The tendency of an atom to attract a shared pair of electrons

Specific heat capacity

The amount of heat it takes to raise the temperature of 1g of a substance by 1°C

Temperature

Average kinetic energy

Heat/thermal energy

Kinetic energy transferred from areas of high temperature to areas of low temperature

Alloy

Mixture of a base metal and an added element

Enthalpy

Amount of heat in a system

Standard enthalpy of combustion (ΔH_c^⦵)

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

Standard enthalpy of formation (ΔH_f^⦵)

The energy change that occurs when one mole of a substance is formed from its constituent elements in their standard state

Entropy (S)

A measure of disorder or randomness in a system, reflecting the distribution of energy among the particles

Entropy change (ΔS)

The difference in entropy between the final and initial states of a system, measuring how much disorder has increased or decreased during a process

Standard entropy (S^⦵)

The entropy change from heating a substance from 0K to 298K (measured in JK^-1mol^-1)