Question

Question number 8

The following reaction is carried out at 25^o C:    

2NO_(g) + O_{2 (g)} → 2NO_{2 (g)}

These are the thermodynamic values associated with this reaction:

ΔS^o_reaction = -147 J K^-1

ΔH^o_reaction = -114 kJ

ΔG^o_reaction = -70 kJ

What is the effect of changing the reaction temperature to 500 K?   

Question 8 options:

	all of the answers are correct
	none of the answers are correct
	the reaction is less spontaneous at 500 K
	the spontaneity of the reaction does not change with temperature
	the reaction is more spontaneous at 500 K
	the reaction is not spontaneous at either temperature

Answer 1

The reaction is :

2NO (g) + O2 (g) --------------> 2NO2 (g)

Now, using formula ∆G ° = ∆H° - T * ∆S°

Putting the values of T , ∆H° and ∆S° , and calculating ∆G, we get

=> ∆G = -114 * 1000 J - (500K)(-147 JK^-1)

=> ∆G = - 114000 J + (500K)(147 JK^-1)

=> ∆G = -114000J + 73500 J

=> ∆G = -40500 J

=> ∆G = -40.5 kJ

Thus, on changing the Reaction temperature to 500K, the value of ∆G changes from -70kJ to -40.5 kJ. The value becomes greater than the previous one but still it is negative. Hence, the reaction will be spontaneous but less spontaneous as compared to the previous one.

Hence, the Reaction is less spontaneous at 500K.