Question

When $1g$ of water changes from liquid to vapour phase at constant pressure of $1atm$, the volume increases from $1cc$ to $1671cc$. The heat of vaporization at the pressure is $540cal/g$. Find the increase in internal energy of water.

• A. $2268J$
• B. $2098.8J$
• C. $2000J$
• D. $2019.65J$

Answer 1

Answer: (B)

$2098.8J$

Volume change = $dv=1671\times {10}^{-6}{m}^3$
Pressure, $P=1.013\times {10}^{5}Pa$
Work done = pressure x volume change=$Pdv$= 1$69.2J$
Latent heat of vaporization =$540cal/g$ =$2268J/g$
Increase in internal energy = $\text{latent heat of vaporization - work done by the water}=2268-169.2=2098.8J$