1.

For a chemical reaction the values of ∆H and ∆S at 300 K are – 10 kJ mol-1 and -20 J mol-1 respectively. What is the value of AG of the reaction? Calculate the ∆G of a reaction at,600K assuming ∆H and AS values are constant. Predict the nature of the reaction.

Answer»

Given,

∆H =- 10 kJ mol = -10000 J mol-1 

∆S = -20 JK-1 mol-1 

T = 300 K 

∆G = ? 

∆G = ∆H – T∆S 

∆G = – 10 kJ mol-1 -300 K x (-20 x 10-3) kJ K-1 mol-1 

∆G = (-10 + 6) kJ mol-1 

∆G =-4 kJ mol-1

At 600 K,

∆G = – 10 kJ mol-1 -600 K x (-20 x 10-3) kJ K-1 mol-1 

∆G =(-10+12) kJ mol-1 

∆G = +2 kJ mol-1

The value of ∆G is negative at 300K and the reaction is spontaneous, but at 600K the value ∆G becomes positive and the reaction is non-spontaneous.


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