Question

Calculate the maximum work done, when pressure on $14gram$ of hydrogen gas is reduced from $20$ to $2atm$ at a constant temperature of $273K$. Consider the gas behave ideally.

• A. $-8.8kcal$
• B. $-6.5kcal$
• C. $-2.5kcal$
• D. $-4.9kcal$

Answer 1

The correct option is A $-8.8kcal$

Work done is maximum means the process is reversible process and for isothermal reversible process :
$w=-2.303nRTlog\frac{P_1}{P_2}$

n = number of moles of hydrogen
$n=\frac{\text{given weight}}{\text{molar mass}}$ = $\frac{14}{2}=7mol$

Given : $P_1=20atm$
$P_2=2atm$
$T=273K$
$R=2cal/K.mol$
so,
$w=-2.303\times 7\times 2\times 273\times log\frac{20}{2}$
= $-8802.06cal$
or $-8.8kcal$