Question

Find the work done when $2$ moles of hydrogen expands isothermally from $15$ L to $50$ L against a constant pressure of 1 atm at ${25}^{0}C$.

• A. $820.8cal$
• B. $-848.2cal$
• C. $84.7cal$
• D. $-848.2kcal$

Answer 1

The correct option is B $-848.2cal$

We know, work done for an isothermal process is given as:
$W=-P_{ext}(V_2-V_1)$
where $P_{ext}$= external pressure = 1 atm
$V_2$= final volume = 50 L
$V_1$ = initial volume = 15 L
$W=-1\times 35=-35Latm$
and $1Latm=101.3J$
So, $W=-35\times 101.3J=-3545.5J$
We know $1cal=4.18J$
$W=\frac{-3545.5}{4.18}cal$
so, $W=-848.2cal$