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CAIE A-Level Chemistry 24.2.10 Gibbs Energy and Cell Potential

Practise calculating standard Gibbs energy from cell potential, electron number and Faraday’s constant.

Syllabus
2028–2030
Course
Chemistry 9701
Level
A2

Exam points

  • identify n as moles of electrons transferred in the balanced overall cell reaction
  • substitute E°cell in volts and F in C mol−1 into ΔG° = −nE°cellF to obtain J mol−1
  • convert the result to kJ mol−1 and connect positive E°cell with negative ΔG°

24.2.10—Gibbs free energy and cell potential question 1

[Maximum number: 6]

Some electrode potentials are shown in Table 3.1.

Table 3.1

Table 3.1

Question (a)

(a)

Another electrochemical cell is set up using an Fe2+/Fe\mathrm{Fe}^{2+} / \mathrm{Fe} electrode and an alkaline ClO−/Cl−\mathrm{ClO}^{-} / \mathrm{Cl}^{-} electrode under standard conditions.

Calculate the value of ΔG⊖\Delta G^{\ominus} for the cell.
ΔG⊖=\Delta G^{\ominus}=kJmol−1\mathrm{kJ} \mathrm{mol}^{-1}

[ 3 ]

Question (b)

(b)

Iron(II) chloride, FeCl2\mathrm{FeCl}_{2}, is oxidised by chlorine to form iron(III) chloride, FeCl3\mathrm{FeCl}_{3}, under standard conditions.

2FeCl2( s)+Cl2( g)→2FeCl3( s)2 \mathrm{FeCl}_{2}(\mathrm{~s})+\mathrm{Cl}_{2}(\mathrm{~g}) \rightarrow 2 \mathrm{FeCl}_{3}(\mathrm{~s})
ΔH⊖=−128 kJ mol−1\Delta H^{\ominus}=-128 \mathrm{~kJ} \mathrm{~mol}^{-1}
Table 3.2

Table 3.2

[ 3 ]

Question (i)

(i)

Use Table 3.2 and other data to calculate the Gibbs free energy change, ΔG⊖\Delta G^{\ominus}, for this reaction.

Show your working.

ΔG⊖=\Delta G^{\ominus}=
kJ mol−1\mathrm{kJ} \mathrm{~mol}^{-1}
[ 3 ]
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