Question

Choose all of the statements from below which correctly describe issues pertaining to the relationship between the emf of a reaction and its Gibbs free energy change.

(A) The Gibbs free energy change and emf values of a reaction have opposite algebraic signs (+ vs. -).
(B) A Gibbs free energy change involves coulombs of substances whereas an emf involves moles of electrons.
(C) Electron stoichiometry must be used to interconvert a Gibbs free energy change and a reaction emf.
(D) A Gibbs free energy change involves moles of substances whereas an emf involves coulombs of electrons.
(E) Faraday's constant is used to interconvert coulombs of electrons and moles of electrons.

Answer 1

In electrochemistry, electron stoichiometry and Faraday's constant correctly relate the emf of a reaction to its Gibbs free energy change, whereas statements about the algebraic signs and incorrect associations with coulombs are false.

Step-by-step explanation:

Statements B and D incorrectly describe the relationship between the emf of a reaction and its Gibbs free energy change, mainly because the Gibbs free energy change involves energy associated with mole quantities of substances and not coulombs, which are related to the electric current. Statement A is incorrect as the Gibbs free energy (ΔG) and the electromotive force (emf) of a reaction typically do not have opposite algebraic signs; instead, a spontaneous reaction has a negative ΔG and a positive emf.

Statement C is correct; electron stoichiometry must indeed be used to interconvert Gibbs free energy and the reaction emf. This is because the Gibbs free energy change (ΔG) of a reaction at constant temperature and pressure is related to the electrical work that can be performed by the reaction, which is a function of the number of electrons transferred (n), the Faraday's constant (F), and the cell potential (Eº). Statement E is also correct as Faraday's constant is used to interconvert moles of electrons to coulombs in electrochemical calculations.