Question

$1cc$ of water becomes $1681cc$ of steam when boiled at a pressure of ${10}^{5}N{m}^{-2}$. The increasing internal energy of the system is
(Latent heat of steam is $540$ $cal$ $g^{-1}$, $1$ $cal=4.2J$)

• A. $300cal$
• B. $500cal$
• C. $225cal$
• D. $600cal$
• E. $1000cal$

Answer 1

The correct option is B $500cal$

Initial volume of water $=V_1=1{cm}^3$
Volume of steam $=V_2=1681{cm}^3$
Change in volume $dV=V_2-V_1=1681$
$=1680{cm}^3$
$=1680\times {10}^{-6}{m}^3$
Pressure $p={10}^{5}N/m^2$
$dQ=mL=1\times 540\times 4.2$
$=22.68J$
$dW=pdV$
$={10}^5\times 1680\times {10}^{-6}=168$
Internal energy $dU=2268-168=2100J$
$=500cal$