Chemistry - Thermodynamics - I Question with Solution | TestHub
The vapour pressure of water at 353 K is 532 mm Hg. The external pressure on H₂O (l) taken in a cylinder fitted with frictionless movable piston initially containing 0.9 L (= 0.9 kg) of H₂O (l) at 353 K is increased to 1 atm at the constant temperature. Then, heat is supplied keeping the pressure constant till 0.45 L of H₂O (l) is evaporated to form H₂O (g) at 373 K. Assume the internal energy of liquid to be dependent only on temperature. Answer the following questions by carefully observing the diagrams and the data provided. Given:
Specific heat of H₂O (l) = 4.2 J/°C-g
ΔHvap at 373 K and 1 atm = +40 kJ/mol
1 L-atm = 100 J
R = 8 J/K-mol
Total change in enthalpy (in kJ) going from State 1 to State 3 is
Options:
Answer:
Solution:
ΔH(1→2) = 27 J ≈ 0.027 kJ (Q25); ΔH(2→3) = qp = 75.6 + 1000 = 1075.6 kJ. Total ΔH = 1075.627 ≈ 1075.6 kJ. Matches (b).
