Entropy is a state function and its value depends on two or three variables temperature (T), Pressure (P) and volume (V). Entropy change for an ideal gas having number of moles (n) can be determined by the following equation.
Δ S = 2.303 nC V log 
+ 2.303 nR log 
Δ S = 2.303 nC p log 
+ 2.303 nR log 
Since free energy change for a process or a chemical equation is a deciding factor of spontaneity, which can be obtained by using entropy change ( Δ S) according to the expression, Δ G = Δ H – T Δ S at a temperature T.
(i) What would be the entropy change involved in thermodynamic expansion of 2 moles of a gas from a volume of 5 L to a volume of 50 L at 25°C [Given R = 8.3 J/mole – K]
Text Solution
Verified by ExpertsCHECK THE SOLUTION.
(i) Δ S = 2.303 x 2 x 8.3 log 
= 38.23 J/K
(ii) Δ S = 2.303 × 1 × C P log 
= 23.03 
C P = 
C V = C P – R = 
– 8.3
(iii) For reaction to be spontaneous,
Δ G < 0 
Δ H – T Δ S < 0
T > 
T > 428.6 K.
If T < 428.6 K so, reaction is non spontaneous.
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