Change in Gibbs free energy at equillibrium

[doulyftbruh]

I understand that the change in Gibbs Free Energy at equillibrium is 0 and this leads to the equation -deltaH=TdeltaS. My questions here is that if a reaction is at equillibrium, how can there be any change in enthalpy or entropy at all? Why wouldn't these terms be 0?

 

[DrDu]

As an equilibrium process, consider the melting of ice. At 0 degrees Celsius, the amount of ice and water in equilibrium is arbitrary. You can now melt some ice with a Bunsen burner, but afterwards, the system will be in equilibrium again. The heat you added to the system equals the change in H. As G, H and S are state functions, the only point which is relevant is that the system is in equilibrium at the beginning of a process and at the end. In the meantime, the system may deviate from equilibrium to drive the reaction.