Question

Unit mass of a liquid with volume $V _ { 2 }$ at a constant external pressure P and temperature T. If the latent heat of evaporation for the given mass is L, then the increase in the internal energy of the system is

• A. Zero
• B. $P \left( V _ { 2 } - V _ { 1 } \right)$
• C. $L - P \left( V _ { 2 } - V _ { 1 } \right)$
• D. L

Answer 1

Answer: (C)

$L - P \left( V _ { 2 } - V _ { 1 } \right)$

Answer 2

$\Delta Q = \Delta V + P \Delta V$⇒ mL = ∆U + P(V₂ – V₁)

⇒ ∆U = L – P (V₂ – V₁) ($\bullet \bullet$ m = 1)