Which statement about ∆G = 0 at equilibrium is true?

Which statement about ∆G = 0 at equilibrium is true?

• A. It implies ∆H is zero
• B. It implies ∆S is zero
• C. It implies T is zero
• D. It implies ∆H = T∆S

Answer: (D)

At equilibrium there is no net thermodynamic drive for the reaction to go in either direction, so ∆G is zero. The relationship ∆G = ∆H − T∆S means that when ∆G is zero, the enthalpy change and the temperature times the entropy change must balance: ∆H = T∆S. This shows that at that temperature, the heat released or absorbed (enthalpy) and the change in disorder (entropy) conspire to produce no overall Gibbs energy change. Neither ∆H nor ∆S has to be zero by itself; they just have to satisfy this balance. The other statements are not generally true because zero ∆G does not require ∆H or ∆S to vanish, nor does it require temperature to be zero.

At equilibrium there is no net thermodynamic drive for the reaction to go in either direction, so ∆G is zero. The relationship ∆G = ∆H − T∆S means that when ∆G is zero, the enthalpy change and the temperature times the entropy change must balance: ∆H = T∆S. This shows that at that temperature, the heat released or absorbed (enthalpy) and the change in disorder (entropy) conspire to produce no overall Gibbs energy change. Neither ∆H nor ∆S has to be zero by itself; they just have to satisfy this balance. The other statements are not generally true because zero ∆G does not require ∆H or ∆S to vanish, nor does it require temperature to be zero.