Question

Free-energy change, ΔG∘, is related to cell potential, E∘, by the equation ΔG∘=−nFE∘ where n is the number of moles of electrons transferred and F=96,500C/(mol e−) is the Faraday constant. When E∘ is measured in volts, ΔG∘ must be in joules since 1 J=1 C⋅V. Part A Calculate the standard free-energy change at 25 ∘C for the following reaction: Mg(s)+Fe2+(aq)→Mg2+(aq)+Fe(s) Express your answer to three significant figures and include the appropriate units.

Answer 1

Answer:

-372000 J or -372 KJ

Explanation:

We have the electrochemical reaction as;

Mg(s)  +  Fe^2+(aq)→  Mg^2+(aq)  +   Fe(s)

We must first calculate the E∘cell from;

E∘cathode -  E∘anode

E∘cathode = -0.44 V

E∘anode = -2.37 V

Hence;

E∘cell = -0.44 V -(-2.37 V)

E∘cell = 1.93 V

n= 2 since two electrons were transferred

F=96,500C/(mol e−)

ΔG∘=−nFE∘

ΔG∘= -( 2 * 96,500 * 1.93)

ΔG∘= -372000 J or -372 KJ