Question

$15g$ of ice melts to form water at $0{}^{\circ }C$ . What is the change in entropy?

• A. 18.5
• B. 15
• C. zero
• D. None of these

Answer 1

Answer: (A)

Entropy of a system is a measure of its molecular disorder. The greater the disorder, greater is the entropy. The charge in entropy is given by
$dS=\frac{dQ}{T}$
$=\frac{\text{ Heat absorbed }}{\text{ Absolute temperature }}$
Also, $dQ=mL$ where, $m$ is mass and $L$ the latent heat.
Given, $m=15g,L=80cal/g$
$\therefore dQ=15\times 80=1200cal$
$\therefore dQ=1200\times 4.2=5040J$
Hence, change in entropy is
$dS=\frac{5040}{273}=18.46$
$\approx 18.5$