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What are some common mistakes students make with partial pressure?

1 Answer

Feb 5, 2017

Partial pressure is the pressure exerted by a single gas in a mixture of many gases:

$P_{i} = χ_{i} P$ $P_i = chi_iP$

$P_{i}$ $P_i$ is the partial pressure.

$P$ $P$ is total pressure.

$χ_{i}$ $chi_i$ is the mol fraction of $i$ $i$ in the mixture. $chi_i = n_i/(n_1+n_2+...+n_N)$

Mole fractions must be a ratio of mols for component $i$ with the mols for all components.

Common mistakes:

Taking the ratio of the mols of component $i$ with mols of $j$ , instead of mols of $i$ with total mols. That's the mol ratio, not mol fraction.
Taking a given mass and dividing by the molar mass. That's the mols, not mol fraction...
Taking given masses and finding the ratio of the mass of $i$ with the total mass. That's the mass fraction, not mol fraction.

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