And so our delta S of the surroundings will be a positive value. That's why we have this negative value here. So by using this definition of entropy and by using the second law of thermodynamics, we can basically derive the equation for Gibbs free energy that we can use to basically determine whether or not a reaction is spontaneous. So let's call this equation one and this equation two. We can now take equation two and substitute this quantity into this quantity. So the delta S of the surroundings is equal to negative of the Delta H system divided by the temperature.