Why does decrease of temperature increase spontanity of a reaction?

[scilearner]

Hello everyone,

 

I always though when reactants are heated up, there are more collisions and more like a reaction is to take place. However this is not the case for spontaneous reaction according to Gibbs equation. Why is that? Thanks

[Horza2002]

Thats not stricly true. The equation for change in Gibbs energy is

 

G = H -TS

 

If the reaction has a positive change in entropy (S) then an increase temperature will indeed favour a reaction. However, if the change in entropy is negative then a decrease in temperature will make a more favourable gibbs energy.

 

This arises because the entropy of a system depends greatly on the temperature of a system