Thermodynamics · Question 3

Considering ideal gas behavior, the expansion work done (in kJ) when 144 g of water is electrolyzed completely under constant pressure at 300 K is . Use: Universal gas constant (R) = 8.3 J K-1 mol-1 ; Atomic mass (in amu): H = 1, O = 16

Answer

-29.95 to -29.8

Solution

2H2O(l) 2H2(g) + O2(g)

144 g water = 8 mol, which gives 8 mol H2 + 4 mol O2 = 12 mol gas (liquid volume neglected).

w = -P V = - ngRT = -12 8.3 300 = -29880 J = −29.88 kJ

(Work done by the system is 29.88 kJ. The official key accepts −29.95 to −29.8 or 29.8 to 29.95.)

Answer: −29.88