Question

A certain of gas is expanded from (1L,10atm) to (4L,5atm) against a constant external pressure of 1atm. If the initial temperature of a gas is 300K, and the heat capacity of the process is 50J/degree celsius. The change during the reaction is: (1L atm= 100J)

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

Answer 1

Answer: (B)

$\Delta H=15.7KJ$

For the state 1

$PV=nRT$

$1\times 10=n\left(0.0821\right)\left(300\right)$

$n=0.4$

For the state 2

$PV=nRT$

$4\times 5=0.4\times \left(0.0821\right)\left(T_2\right)$

$T_2=600K$

$\Delta U=q+W$

$=50\left(\Delta T\right)+(-P_{ex})\left(\Delta V\right)$

$=50(600-300)-\left(1\right)(4-1)$ (In L-atm)

$=15000-300$ (In joule)

$=14700J$

$\Delta H=\Delta U+\Delta \left(PV\right)$

$=14700+(5\times 4-10\times 1)\times 100$ (1 L-atm = 100J)

$=15700J$

$=15.7kJ$ or