Question

predict whether a reaction with triangle H and a triangle S will be spontaneous , nonspontaneous or temperature dependant. Explain your answer

Answer 1

A reaction with triangle H and a triangle S will be spontaneous , nonspontaneous or temperature dependant .This all depend on Triangle G (i.e gibbs free energy)

If triangle G < 0 ; Then reaction is Spontaneous

If triangle G > 0 ; Then reaction is non Spontaneous.

The equation is    ∆G = ∆H – T ∆S

For spontaneous reaction; (i.e ∆G < 0) :

1. ∆H is -ve , ∆S is +ve     (or)

2. ∆H is -ve , ∆S is -ve (∆H > T ∆S)    (or)

3. ∆H is +ve , ∆S is +ve (∆H < T ∆S)  

For non spontaneous reaction; (i.e ∆G > 0) :

1. ∆H is +ve , ∆S is -ve      (or)

2. ∆H is +ve , ∆S is +ve (∆H > T ∆S)      (or)

3. ∆H is -ve , ∆S is -ve (∆H < T ∆S)

Temperature dependence :

Sometimes change in temperature value changes the spontaneous reaction to non spontaneous and vice versa.

∆G = ∆H – T ∆S

for example;    If ∆H is -ve and   ∆S is also -ve .

then for ∆H > T ∆S it is spontaneous reaction and for ∆H < T ∆S it is non spontaneous.

This change is due to the change in Temperature value.