Question

For A+B⇌C, the ΔG∘f are 402.0 kJ/mol, 387.7 kJ/mol, and 500.8 kJ/mol, respectively. What is ΔG∘rxn? If both entropy and enthalpy changes are positive for this reaction at 25∘C, which one drives it?

Answer 1

Answer:$\Delta G^o_{rxn}=-288.9 kJ.mol$

Factor which will drive this reaction will entropy.

Explanation:

A+B⇌C

Gibbs free energy of formation of A = $\Delta G_a=402.0 kJ/mol$

Gibbs free energy of formation of B = $\Delta G_b=387.7 kJ/mol$

Gibbs free energy of formation of C = $\Delta G_c=500.8 kJ/mol$

$\Delta G^o_{rxn}=(\Delta G_c)-(\Delta G_b+\Delta G_a)$

$\Delta G^o_{rxn}=500.8 kJ/mol-387.7 kJ/mol-402.0 kJ/mol$

$\Delta G^o_{rxn}=-288.9 kJ.mol$

Generally Gibbs free energy is determined by equation:

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

If both entropy and enthalpy changes are positive for this reaction , factor which will drive this reaction will entropy.

Higher the entropy more will be higher negative value of the product $T\Delta S$ which will finally give negative value of Gibbs free energy for the reaction at 25 C..