Question

A certain mass of gas is expanded from (1L, 10 atm) to (4L, 5 atm) against a constant external pressure of 1 atm. If initial temperature of gas is 300 K and the heat capacity of process is 50 J/⁰C. Then the enthalpy change during the process is (1L atm~ 100 J)

• A. $\Delta$H = 15 kJ
• B. $\Delta$H = 15.7 kJ
• C. $\Delta$H = 14.4 kJ
• D. $\Delta$H = 14.7 kJ

Answer 1

Answer: (B)

$\Delta$H = 15.7 kJ

Answer 2

State 1 $\longrightarrow$ State 2

(1 L, 10 atm, 300 K) (4L, 5 atm, 600 K)

Heat given, q = 50 ´ (600 – 300) = 15000 J

W = – Pext (V2 – V1) = – 1 (4–1) = – 3 L atm = – 300 J

$\Delta$E = q + W = 15000 – 300 = 14700 J

$\Delta$H = $\Delta$E + P2V2 – P1V1 = 14700 J + (20 – 10) ´ 100 J = 15.7 KJ