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You are watching: Is water vapor an ideal gas


How to accurately estimate the molar concentration that pure water vapour in ~ 298 K? deserve to ideal gas regulation be applied to water vapour to calculation the molar concentration?


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Yes, for countless practical purposes, you may use the ideal gas law additionally as one approximation because that water vapour.

However, you need two independent quantities to explain the state the the gas, for example temperature and also pressure. The offered temperature of $T=298 mathrm K$ alone is no enough. The right gas legislation does not offer you a worth for the 2nd quantity.

For example, presume equilibrium conditions for saturated heavy steam at a temperature that $T=298.00 mathrm K$, the corresponding pressure is $p=3141.7 mathrmPa$.

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Using the right gas legislation yields a concentration of

$$frac nV=frac pRT=frac3141.7 mathrmPa8.314462618 mathrmJ mol^-1 K^-1 imes298.00 mathrm K=1.2680 mathrmmol m^-3$$

The actual worth for water vapour in ~ this temperature and pressure is

$$frac nV=1.2701 mathrmmol m^-3$$

Thus, utilizing the ideal gas regulation introduces one error of around $0.2 \%$ in this case, which could be agree for countless practical purposes.


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edited Jun 15 "19 at 9:29
answer Nov 1 "18 in ~ 22:38
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