Question

For the reaction c2h6 (g) → c2h4 (g) + h2 (g) δh° is +137 kj/mol and δs° is +120 j/k ∙ mol. this reaction is ________. question 10 options: spontaneous only at high temperature spontaneous at all temperatures spontaneous only at low temperature nonspontaneous at all temperatures

Answer 1

Answer: spontaneous only at high temperature

Explanation: $C_2H_6(g)\rightarrow C_2H_4(g)+H_2(g)$

The Gibbs free energy change is given by:

$\Delta G=\Delta H-T\Delta S$

$\Delta G$ = Gibbs free energy

when $\DeltaG$= +ve, reaction is non spontaneous

$\DeltaG$= -ve, reaction is spontaneous

$\DeltaG$= 0, reaction is in equilibrium

$\Delta H$ = enthalpy change = endothermic = +137 KJ

$\Delta S$ = entropy change = +120 J/K

$\Delta G=(+)-T(+)$

$\Delta G=(+)(-ve)$

Now $\Delta G= -ve$ when $T\Delta S$ has more value than $\Delta H$

Thus reaction is spontaneous at high temperatures.

Answer 2

When  ΔH is positive and ΔS is positive, the reaction is spontaneous at high temperature.

In order to answer the question, we must define he following terms;

• Exothermic reaction: This is a reaction in which the enthalpy change is negative
• Endothermic reaction: This is a reaction in which he enthalpy change is positive

Let us recall that;

ΔG = ΔH - TΔS

Hence, when ΔH is positive and ΔS is positive, the reaction is spontaneous at high temperature.

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