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Enthalpy Level Diagrams

Enthalpy level diagrams represent enthalpy changes and show the relative levels of energy of the reactants and products.The vertical axis is the enthalpy and the horizontal axis is labelled 'progress of the reaction'.Arrows pointing upwards represent endothermic processes and arrows pointing downwards represent exothermic processes. The change in enthalpy is given by:ΔH = Hproducts - HreactantsFor an exothermic reaction ΔH is negative and for an endothermic reaction ΔH is positive.

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Specification: AQA Chemistry (7404), AS-level, 3.1.4.1 Enthalpy change. Topic: Energetics.

Key terms in this lesson

Enthalpy
A measure of the heat energy stored in a chemical system.
Exothermic
Describes a reaction in which energy is transferred from the system to the surroundings, so the enthalpy change is negative.
Endothermic
Describes a reaction in which energy is transferred from the surroundings to the system, so the enthalpy change is positive.

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