Cracking the AP Chemistry Exam

Part IV

Content Review for the AP Chemistry Exam

Chapter 7

Big Idea #5: Laws of Thermodynamics and Changes in Matter

FREE ENERGY CHANGE, ∆G

The standard free energy change, ∆G, for a reaction can be calculated from the standard free energies of formation, G°_f, of its products and reactants in the same way that ∆S° was calculated.

∆G° = Σ∆G°_{f products} − Σ∆G°_{f reactants}

For a given reaction

· if ∆G is negative, the reaction is thermodynamically favored

· if ∆G is positive, the reaction is thermodynamically unfavored

· if ∆G = 0, the reaction is at equilibrium