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

For the reaction c2h6 (g) → c2h4 (g) + h2 (g) δh° is +137 kj/mol and δs° is +120 j/k ∙ mol. This reaction is spontaneous only at high temperature.
here the values of δh° is +137 kj/mol and δs° is +120 kj/mol. so, both the value are wit the sign "+". when both values are positive than the reaction is not spontaneous at low temperature, the reaction is spontaneous only at high temperature.

Answer 2

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.