Enthalpy Changes

01Enthalpy Changes

Enthalpy and enthalpy change

This section covers enthalpy, enthalpy change and energy transfer between a chemical system and its surroundings.

Enthalpy change at constant pressure

Enthalpy, HH, describes the energy content of a chemical system. A chemical reaction can change this energy.

Enthalpy change, ΔH\Delta H, is the heat energy change measured under conditions of constant pressure.

An enthalpy change may be positive or negative depending on the direction in which energy is transferred.

System

The system consists of the substances involved in the chemical change.

Surroundings

The surroundings are everything outside the reacting substances, including the apparatus and wider environment.

When an enthalpy change occurs, energy passes between the system and its surroundings.

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