BRAINCAKEEnthalpy Change ΔH
Enthalpy is a measure of the total energy of a chemical system. The enthalpy change of a process is the heat energy that is transferred between the system and its surroundings at constant pressure.
The difference in the enthalpy of the reactants and products is called the enthalpy change ΔH.
ΔH = Hproducts - Hreactants
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Key terms in this lesson
- 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.
- Standard conditions
- A pressure of 100 kPa, a temperature of 298 K, and, for solutions, a concentration of 1 moldm-3.
More in Energetics
- Endothermic and Exothermic Reactions
- Physical States of Reactants and Products
- Enthalpy Level Diagrams
- Standard Enthalpies
- Measuring the Enthalpy Change of A Reaction
- Simple Colorimeter
- Flame Colorimeter
- Neutralisation Reactions
All 24 lessons in Energetics · All AQA AS-level Chemistry topics