9.1- Enthalpy Changes

Enthalpy Change (ΔH)

The amount of energy released or absorbed during a chemical reaction.

Exothermic Reaction

A reaction that releases energy into the surroundings, indicated by a negative ΔH.

Endothermic Reaction

A reaction that absorbs energy from the surroundings, indicated by a positive ΔH.

Activation Energy (Ea)

The minimum energy required for a reaction to take place.

Standard Conditions

Conditions defined as 100 kPa, 298 K (25°C), and 1 mol dm-3 for solutions, under which ΔH values are measured.

Standard Enthalpy Change of Reaction (ΔrH)

The enthalpy change associated with a stated reaction in mole quantities shown in the chemical equation under standard conditions.

Standard Enthalpy Change of Formation (ΔfH)

The enthalpy change associated with the formation of 1 mole of a compound from its elements under standard conditions.

Standard Enthalpy Change of Combustion (ΔcH)

The enthalpy change for the complete combustion of 1 mole of a substance under standard conditions.

Standard Enthalpy Change of Neutralisation (ΔneutH)

The enthalpy change associated with the formation of 1 mole of water from a neutralisation reaction between an acid and a base.

Conservation of Energy

Energy cannot be created or destroyed; it can only be transferred between the system and the surroundings.