Question

A piece of ice (heat capacity $=2100Jk{g}^{-1}{}^{\circ }{C}^{-1}$ and latent heat $=3.36\times 10^{5}Jk{g}^{-1}$ ) of mass $m$ grams is at $-5^{\circ }C$ at atmospheric pressure. It is given $420J$ of heat so that the ice starts melting. Finally when the ice-water mixture is in equilibrium, it is found that $1g$ of ice has melted. Assuming there is no other heat exchange in the process, the value of $m$ is

• A. 4
• B. 6
• C. 8
• D. 10

Answer 1

Answer: (C)

$\left[m\times 2100\times 5+1\times 3.36\times 10^5\right]\times 10^{-3}$
$=420$ where $m$ is in grams.
or $m\times 2100\times 5\times 10^{-3}+336=420$
or $m\times 2100\times 5\times 10^{-3}=84$ or
$m=\frac{84}{2100\times 5\times 10^{-3}}=8g$