Cliffs AP Chemistry, 3rd Edition

Energy and Spontaneity

Key Terms

Words that can be used as topics in essays:

chemical thermodynamics

endothermic

enthalpy change, ∆H

entropy change, ∆S

exothermic

first law of thermodynamics

free-energy change, ∆G

free energy of formation, ∆Gf

Gibbs-Helmholtz equation

second law of thermodynamics

surroundings

system

third law of thermodynamics

work

Key Concepts

Equations and relationships that you need to know:

• ∆H°= Σ∆Hf°products−Σ∆Hf°reactants
  ∆S°= Σ∆S°products−Σ∆S°reactants
  ∆Suniv= ∆Ssys+ ∆Ssurr

∆Ssurr=-∆THsysif system and surroundings are at same T

∆G°= Σ∆G°products−Σ∆G°reactants

∆G°< 0: spontaneous in forward direction

∆G°> 0: nonspontaneous in forward direction

∆G°= 0: equilibrium

∆G°= ∆H°−T∆S°

∆E= q +w

∆G°= −RT ln Kwhere R= 8.314 J / (K ⋅mole)

if K > 1, then ∆G°is negative; products favored at equilibrium

if K= 1; then ∆G°= 0; reactants and products equally favored at equilibrium

if K< 1, then ∆G°is positive; reactants are favored at equilibrium