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Phase Transformations

Problem 2.218

A water vapour filling the space under the piston of a cylinder, is compressed (or expanded) so that it remains saturated all the time, being just on the verge of condensation. Find the molar heat capacity \(C\) of the vapour in this process as a function of temperature \(T,\) assuming the vapour to be an ideal gas and neglecting the specific volume of water in comparison with that of vapour. Calculate \(C\) at a temperature \(t=100^{\circ} \mathrm{C} .\)

Reveal Answer
2.218.C=Cp−qM/T=−74 J/(K⋅mol), where Cp==Rγ/(γ−1).\begin{array}{l} 2.218 . C=C_{p}-q M / T=-74 \quad \mathrm{~J} /(\mathrm{K} \cdot \mathrm{mol}), \quad \text { where } \quad C_{p}= \\ =R_{\gamma} /(\gamma-1) . \end{array}
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