Explain Gibb’s energy.

Gibb’s energy is a thermodynamic quantity of a system. Gibb’s energy is amount of energy available from system which can be put to useful work at constant temperature and pressure.
It gives us an idea of spontaneity of reaction
$\mathrm{\Delta G}=\mathrm{\Delta H}-\mathrm{T\Delta S}$
Eg: $∆$G = negative for spontaneous reaction.
$∆$G = positive for non-spontaneous reactions
$∆$G = zero for equilibrium reactions.