Engineering
Chemistry
Gibbs Free Energy Calculations and Third Law
Question

Match the thermodynamic processes given under Column I with the expressions given under Column II. 

Column I Column II
(A) Freezing of water at 273 K and 1 atm (P) q = 0
(B) Expansion of 1 mol of an ideal gas into a vacuum under isolated conditions (Q) w = 0
(C) Mixing of equal volumes of two ideal gases at constant temperature and pressure is an isolated container (R) ΔSsys < 0
(D) Reversible heating of H2(g) at 1 atm from 300 K to 600 K, followed by reversible cooling to 300 K at 1 atm. (S) ΔU = 0
  (T) ΔG = 0
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Solution

The correct option is A

(A – R, T) (B – P, Q, S) (C – P, Q, S) (D – P, Q, S, T)

(A) H2O(l) → H2O(s) at 273 K. & 1 atm

ΔH = -ve = q
ΔSsys < 0, ΔG = 0
w ≠ 0 (as water expands on freezing), ΔU ≠ 0

(B) Free expansion of ideal gas.

q = 0
w = 0
ΔU = 0

ΔSsys > 0

ΔG < 0

(C) Mixing of equal volume of ideal gases at constant pressure & temp in an isolated container

q = 0, w = 0, ΔU = 0, ΔSsys > 0, ΔG < 0

(D) H2(g) 300 K ⟶ 600 K ⟶ 300 K

(Reversible Heating, 1 atm) (Reversible Cooling, 1 atm)

q = 0, w = 0, ΔU = 0, ΔG = 0, ΔSsys = 0