5.2.2
Enthalpy and
Entropy
Section 5.2.2 covers entropy as a measure of the dispersal of energy, the entropy of solids, liquids and gases and of reactions that change the number of gas molecules, calculating the entropy change of a system from standard entropies, feasibility in terms of TΔS and ΔH, the Gibbs’ equation ΔG = ΔH − TΔS with calculations, feasibility when ΔG is negative, and the limits of ΔG predictions in terms of kinetics.
Revision Notes
Work through 5.2.2 Enthalpy and Entropy in a structured sequence.
Entropy and the Direction of Change
Entropy: disorder and the dispersal of energy, entropy and temperature, changes of state, dissolving, gas moles and the natural direction of change.
Start revisingCalculations
Calculating Entropy Changes
Entropy calculations: ΔS from standard entropies, units and worked examples.
Start revisingTemperature
Feasibility, Gibbs Energy and Temperature
Feasibility: ΔG = ΔH − TΔS, the sign of ΔG, the effect of temperature and the temperature at which a reaction becomes feasible.
Start revisingKinetic Stability
Thermodynamic and Kinetic Stability
Thermodynamic and kinetic stability: feasible but slow reactions, activation energy and the limits of ΔG and ΔStotal predictions.
Start revising5.2.2 Enthalpy and Entropy – OCR A Level Chemistry A
The following OCR A learning outcomes state what candidates should be able to do. Wording is taken from the OCR A Level Chemistry A (H432) specification.
5.2.2 Enthalpy and entropy
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