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Gibb's Energy and Nernst Equation

When compared...

Question

When compared to $Δ G^{o}$ for the formation of ${A l}_{2} O_{3}$ , the $Δ G^{o}$ for the formation of ${C r}_{2} O_{3}$ is:

A

higher

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B

lower

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C

same

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D

unpredicted

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Solution

The correct option is B lower
When compared to $Δ G^{o}$ for the formation of ${A l}_{2} O_{3}$ , the $Δ G^{o}$ for the formation of ${C r}_{2} O_{3}$ is lower (less negative). Hence, aluminum is used as reducing agent for reduction of $C r_{2} O_{3}$ .
$C r_{2} O_{3} + 2 A l \to A l_{2} O_{3} + 2 C r$
The reaction proceeds in the forward direction as $A l_{2} O_{3}$ is more stable than $C r_{2} O_{3}$ .

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Similar questions

Q. If the heats of formation of

{A l}_{2} O_{3} (s)

{C r}_{2} O_{3} (s)

1596 k J

1134 k J

(both exothermic) respectively. Calculate

Δ H

of the thermite reaction.

{C r}_{2} O_{3} (s) + 2 A l (s) ⟶ 2 C r (s) + {A l}_{2} O_{3} (s)

Q. The standard Gibbs free energies for the reactions at

1773 K

are given below:

C (s) + O_{2} (g) ⟶ C O_{2} (g); Δ G^{o} = - 380 k J {m o l}^{- 1}

C (s) + O_{2} (g) ⇌ 2 C O (g); Δ G^{o} = - 500 k J {m o l}^{- 1}

Discuss the probability of reducing

{A l}_{2} O_{3}

P b O

with carbon at this temperature,

4 A l + 3 O_{2} (g) ⟶ 2 {A l}_{2} O_{3} (s); Δ G^{o} = - 22500 k J {m o l}^{- 1}

2 P b + O_{2} (g) ⟶ 2 P b O (s); Δ G^{o} = - 120 k J {m o l}^{- 1}

Q. The standard enthalpies of formation of

A l_{2} O_{3}

C a O

- 1675 k J m o l^{- 1}

- 635 k J m o l^{- 1}

respectively. For the reaction

3 C a O + 2 A l \to 3 C a + A l_{2} O_{3}

the standard reaction enthalpy,

Δ_{r} H^{0} =

________kJ. (Round off to the Nearest Integer)

Q. The standard enthalpies of formation of

A l_{2} O_{3}

C a O

- 1675 k J m o l^{- 1}

- 635 k J m o l^{- 1}

respectively.
For the reaction,

3 C a O + 2 A l \to 3 C a + A l_{2} O_{3}

the standard reaction enthalpy,

Δ_{r} H^{0}

=______kJ (Rounded off to the Nearest Integer).

Q. The Gibbs energy for the decomposition of

{A l}_{2} O_{3}

500^{o} C

\frac{2}{3} {A l}_{2} O_{3} \to \frac{4}{3} A l + O_{2}; Δ_{r} G = + 96 k J

The voltage needed for the electrolytic reduction of aluminium oxide (

{A l}_{2} O_{3}

500^{o} C

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