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The density of ice at $0^{\circ}\mathrm{C}$ is 0.915 gram/cc and that of liquid water at $0^{\circ}\mathrm{C}$ is 0.99987 gram/cc. The work done for melting 1 mole of ice at 1.00 bar (assuming work is done only due to expansion) is approximately
A0.17 J
B$1.7 \times 10^{3} \, \mathrm{J}$
C$1.7 \times 10^{-6} \, \mathrm{J}$
Dcan't be determined
Answer & Solution
Correct answer: A. 0.17 J
For melting at constant pressure, the expansion work is $$w=-P\Delta V.$$ We need the volume change for $1$ mole, whose mass is $18$ gram.
Volume of ice:
$$V_{\text{ice}}=\frac{18}{0.915}\,\text{cc}\approx 19.67\,\text{cc}.$$
Volume of water:
$$V_{\text{water}}=\frac{18}{0.99987}\,\text{cc}\approx 18.00\,\text{cc}.$$
Hence,
$$\Delta V=V_{\text{water}}-V_{\text{ice}}\approx -1.67\,\text{cc}=-1.67\times 10^{-6}\,\text{m}^3.$$
At $1.00$ bar,
$$P=10^5\,\text{Pa}.$$
Therefore,
$$w=-P\Delta V=-(10^5)(-1.67\times 10^{-6})\,\text{J}\approx 0.17\,\text{J}.$$
So the magnitude of work done is approximately $0.17\,\text{J}$, which matches option $\text{A}$.
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