Question

Does, negative $∆\mathrm{G}$ mean a spontaneous reaction?

Answer 1

1. Gibbs free energy- Gibbs free energy is described as the thermodynamic potential which can evaluate the maximum amount of work at constant temperature and pressure in a thermodynamically closed system
2. Negative Gibbs free energy $(∆{\mathrm{G}}_{\mathrm{rxn}})$ means that the reaction is spontaneous and positive Gibbs free energy $(∆{\mathrm{G}}_{\mathrm{rxn}})$ indicates that process is nonspontaneous. When $∆\mathrm{G}=0$, it indicates that equilibrium is achieved.
3. Mathematically, we can write- $∆{\mathrm{G}}_{\mathrm{rxn}}=∆{\mathrm{H}}_{\mathrm{rxn}}-\mathrm{T}∆{\mathrm{S}}_{\mathrm{rxn}}$, where- $∆{\mathrm{G}}_{\mathrm{rxn}}$ is the Gibbs free energy change for a reaction, $∆{\mathrm{H}}_{\mathrm{rxn}}$ is the enthalpy change for a reaction, $\mathrm{T}$is the temperature and $∆{\mathrm{S}}_{\mathrm{rxn}}$is the entropy change for the reaction.

When a reaction is exothermic $∆{\mathrm{H}}_{\mathrm{rxn}}<0$ and entropy change in the reaction is positive $(∆{\mathrm{S}}_{\mathrm{rxn}}>0)$, we get $∆{\mathrm{G}}_{\mathrm{rxn}}<0$ which means a spontaneous reaction.

When a reaction is exothermic $∆{\mathrm{H}}_{\mathrm{rxn}}<0$ and entropy change in the reaction is small negative, we get $∆{\mathrm{G}}_{\mathrm{rxn}}<0$ which means a spontaneous reaction.

When a reaction is endothermic $∆{\mathrm{H}}_{\mathrm{rxn}}>0$ and entropy change in the reaction is large positive $(∆{\mathrm{S}}_{\mathrm{rxn}}>>0)$, we get $∆{\mathrm{G}}_{\mathrm{rxn}}<0$ which means a spontaneous reaction.

When a reaction is endothermic $∆{\mathrm{H}}_{\mathrm{rxn}}>0$ and entropy change in the reaction is high negative, we get $∆{\mathrm{G}}_{\mathrm{rxn}}>0$ which means a non-spontaneous reaction.

So, yes negative $∆\mathrm{G}$ means a spontaneous reaction.