Question

Assuming that water vapour is an ideal gas, the internal energy (U)when 1 mol of water is vaporized at 1 bar pressure and 100⁰C, (Given: Molar enthalpy of vaporization of water at 1 bar and 373 K = 41 kJ mol ^-1 an R=8.3 J mol^-1K^-1) will be 

(A) 4100 kJ mol^-1 

(B) 3.7904 kJ mol^-1 

(C) 37.904 kJ mol^-1 

(D) 41.00 kJ mol^-1

Answer 1

Correct option (C) 37.904 kJ mol^-1

Explanation:

∆n_g =1-0=1

∆H =∆U +∆n_gRT

∆H =∆U +∆n_gRT

= 41 – 8.3 × 10^–3 × 373 

= 37.9 kJ mol^–1