Question

Why does Gibbs free energy decrease with temperature?

Answer 1

Free

Energy (G) can either increase or decrease for a reaction when the temperature

increases. It depends on the entropy (S) change.

The

change in a quantity is represented by the Greek letter delta. But let me use

"d" for delta since I cannot type the Greek letter. The equation for

the change in free energy is dG = dH - TdS. Where H is the enthalpy, S is the entropy and T is the Kelvin temperature.

Since the change in G depends on minus T times the change in S, if the entropy

decreases (that means dS is negative) then -TdS is positive. Hence, when the

temperature increases the numeric value of the free energy becomes larger.

Just

the opposite is true if the entropy increases. In this case dS will be positive

and -TdS becomes more negative when the temperature goes up. So, the numeric

value of the free energy becomes smaller.

You

have to be careful with the terminology. A reaction with a delta G of -2000 kJ

gives more free energy than one with a delta G of $-1000kJ$, but -1000 is a

larger number than $-2000!$