(HL) Entropy and spontaneity

Learning objectives

(HL) Define entropy as a measure of the dispersal of energy and matter in a system, give its units of J K⁻¹ mol⁻¹, and predict the sign of the entropy change of a reaction from the change in the number of moles of gas and the change of state

(HL) Calculate a standard entropy change from ΣS(products) − ΣS(reactants) using standard molar entropies

(HL) Calculate the standard Gibbs energy change from ΔG = ΔH − TΔS, converting entropy values from J K⁻¹ mol⁻¹ to kJ K⁻¹ mol⁻¹, and interpret a negative value as the condition for a spontaneous reaction

(HL) Predict how the spontaneity of a reaction changes with temperature from the signs of ΔH and ΔS, and calculate the temperature at which a reaction becomes spontaneous

(HL) Calculate the standard Gibbs energy change of a reaction from standard Gibbs energies of formation

(HL) Relate the standard Gibbs energy change to the equilibrium constant using ΔG = −RT lnK, and interpret the size of K for a strongly positive or strongly negative value of ΔG