Understandings:
• Le Châtelier’s principle for changes in concentration can be explained by the equilibrium law.
• The position of equilibrium corresponds to a maximum value of entropy and a minimum in the value of the Gibbs free energy.
• The Gibbs free energy change of a reaction and the equilibrium constant can both be used to measure the position of an equilibrium reaction and are related by the equation, ∆𝐺 = −𝑅T ln𝐾
Applications and skills:
• Solution of homogeneous equilibrium problems using the expression for Kc.
• Relationship between ∆G and the equilibrium constant.
• Calculations using the equation ∆𝐺 = −𝑅T ln𝐾.
Guidance:
• The expression ∆𝐺 = −𝑅T ln𝐾 is given in the data booklet in section 1.
• Students will not be expected to derive the expression ∆𝐺 = −𝑅T ln𝐾.
• The use of quadratic equations will not be assessed.
Table 6. Relations between Standard Free Energy Changes and Equilibrium Constants
Figure 3. These plots show the free energy versus reaction progress for systems whose standard free changes are (a) negative, (b) positive, and (c) zero. Nonequilibrium systems will proceed spontaneously in whatever direction is necessary to minimize free energy and establish equilibrium.