Question

1 g of water changes from liquid to vapour phase at constant pressure of 1 atmosphere, the volume increases from 1 mL to 1671 mL. The heat of vapourisation at this pressure is 540cal/g.The work done (in J) during phase change is

• A. $450$
• B. $400$
• C. $170$
• D. $250$

Answer 1

The correct option is C $170$

The given process is isobaric, thus
$w=-\int P\Delta V=-P[V_f-V_i]$
$\because P=1atm=1.01\times {10}^5{Nm}^{-2}$
and $\Delta \Delta V=1671-1=1670mL$
$=1670\times {10}^{3}L=1670\times {10}^{-6}{m}^3$
$\therefore w=1.01\times {10}^5\times 1670\times {10}^{-6}=168.67J$