Category Archives: 1.8 Thermodynamics

Gibbs free-energy change ΔG and entropy change ΔS

Definitions ⦵       Standard pressure (100kPa), usually with a stated temperature (e.g. 298K) ΔG⦵ Gibbs free-energy change, measured in kJ mol−1 ΔH⦵ Enthalpy change, measured in kJ mol−1 T   Temperature measured in Kelvin ΔS⦵ Entropy change, measured in J K−1 mol−1 The feasibility of a physical or a chemical change depends on the balance between the thermodynamic quantities of enthalpy

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Born-Haber cycles

KEY CONCEPTS 1. Enthalpy is heat change of a system under conditions of constant pressure. ΔH⦵ (298 K) represents the standard enthalpy change of a system at 100kPa and at the stated temperature (i.e. 298 K) per mole of the specified substance. The standard state of a substance is the form of the pure substance at 100kPa at the stated temperature (normally quoted as 298 K).

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