Calculation of the Fugacity of Saturated Steam Compute the fugacity of saturated steam at 300°C.

Question

Calculation of the Fugacity of Saturated Steam
Compute the fugacity of saturated steam at 300°C.

Accepted Answer

The saturation pressure of steam at 300°C is 8.581 MPa, and from Illustration 7.3-1 we have [latex]\hat{G}^{\mathrm{V}}[/latex] = -520.5 kJ/kg and [latex]\underline{G}^{\mathrm{V}}[/latex] = -9376.8 J/mol. Following the previous illustration, we have

[latex]\begin{aligned}G^{\mathrm{IG}}\left(300^{\circ} \mathrm{C}, 8.581 \mathrm{MPa} ight) &=\underline{G}^{\mathrm{IG}}\left(300^{\circ} \mathrm{C}, 0.01 \mathrm{MPa} ight)+\int_{0.01 \mathrm{MPa}}^{8.581 \mathrm{MPa}} \frac{R T}{P} d P \\&=-40409+8.314 imes 573.15 \ln 858.1 \\&=-8221.6 \frac{\mathrm{J}}{\mathrm{mol}}\end{aligned}[/latex]

Therefore,

[latex]\begin{aligned}f^{\mathrm{V}}\left(300^{\circ} \mathrm{C}, 8.581 \mathrm{MPa} ight) &=8.581 \mathrm{MPa} \exp \left[\frac{-9376.8-(-8221.6)}{8.314 imes 573.15} ight] \\&=8.581 \mathrm{MPa} imes 0.7847 \\&=6.7337 \mathrm{MPa}\end{aligned}[/latex]

COMMENT

Note that since, at equilibrium, [latex]f^{\mathrm{V}}=f^{\mathrm{L}}[/latex], it is also true that

[latex]f^{\mathrm{L}}\left(300^{\circ} \mathrm{C}, 8.581 \mathrm{MPa} ight)=6.7337 \mathrm{MPa}[/latex]

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