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Gibb's Free Energy

The reaction ...

Question

The reaction $C r_{2} O_{3} + 2 A l \to A l_{2} O_{3} + 2 C r (△ G^{0} = - 421 k J)$ is thermodynamically feasible due to -ve value of $△ G .$ Why does this reaction not take place at room temperature?

Certain amount of activation energy is essential for thermodynamically feasible reactions also.

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Due to high melting point of chromium oxide the reaction does not take place.

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Overall value of

△ G

for the net reaction becomes positive.

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Molecules of

C r_{2} O_{3}

and Al are not oriented properly.

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Solution

The correct option is A Certain amount of activation energy is essential for thermodynamically feasible reactions also.
In thermite process,
${C r}_{2} O_{3} + 2 A l ⟶ {A l}_{2} O_{3} + 2 C r + Q$
It is an exothermic and spontaneous process. It requires more activation energy. At room temperature it does not takes place as activation energy is less.

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Similar questions

Δ_{f} G^{0}

C r_{2} O_{3}

540 {kJ mol}^{- 1}

A l_{2} O_{3}

- 827 {kJ mol}^{- 1}

C r_{2} O_{3}

A l

Δ_{f} G^{0}

C r_{2} O_{3}

540 {kJ mol}^{- 1}

A l_{2} O_{3}

- 827 {kJ mol}^{- 1}

C r_{2} O_{3}

A l

Δ_{r} G^{\circ}

C r_{2} O_{3}

- 540 {kJ mol}^{- 1}

A l_{2} O_{3}

- 827 {kJ mol}^{- 1}

C r_{2} O_{3}

A l

X e O_{3} + 6 H^{+} + 6 e^{-} ⇌ X e + 3 H_{2} O, E^{\circ} = 2.1 V

H_{2} O

A l_{2} O_{3}

M g O

△ G^{0}

\frac{2}{3} A l_{2} O_{3} + 2 M g \to + \frac{4}{3} A l

M g O

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