The standard enthalpy change of reaction ΔrHθ is the enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions, with all reactants and products in their standard states.ΔrHθ always refers to a stated equation and depends on the stoichiometry and balancing numbers of the equation. For example:Ca(s) + ½O2(g) → CaO(s) ΔrHθ = -644.5 kJmol-12Ca(s) + O2(g) → 2CaO(s) ΔrHθ = -1289 kJmol-1
Enthalpy Change of Reaction
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Specification: OCR Chemistry A (H032), AS-level, 3.2.1 Enthalpy changes. Topic: Enthalpy.
Key terms in this lesson
- Stoichiometry
- The reacting ratio of moles of reactants and products in a balanced chemical equation.
- Enthalpy
- A measure of the total energy of a chemical system.
- Enthalpy change
- The heat energy that is transferred between the system and its surroundings during a process carried out at constant pressure.
- Standard conditions
- A pressure of 100 kPa, a temperature of 298 K, and, for solutions, a concentration of 1 moldm-3.
More in Enthalpy
- Enthalpy and Enthalpy Changes
- Endothermic and Exothermic Reactions
- Activation Energy
- Standard Enthalpy Changes and Standard Conditions
- Enthalpy Change of Formation
- Enthalpy Change of Combustion
- Enthalpy Change of Neutralisation
- Measuring the Enthalpy Change of Combustion
All 19 lessons in Enthalpy · All OCR AS-level Chemistry topics