Vapor Pressure Lowering is a colligative property which describes the decrease in vapor pressure of a solution when a solute is added to a solution.

The formula for vapor pressure lowering is:

$\overline{){{\mathbf{P}}}_{{\mathbf{solution}}}{\mathbf{=}}{{\mathbf{\chi}}}_{{\mathbf{solvent}}}{\mathbf{\xb7}}{\mathbf{P}}{{\mathbf{\xb0}}}_{{\mathbf{solvent}}}}$

Where:

P_{solution} is the vapor pressure of the solution

P°_{solvent} is the vapor pressure of pure solvent

X_{solvent} is the mole fraction of the solvent

__Solve for the mole fraction of the solvent:__

__$\overline{){{\mathbf{\chi}}}_{{\mathbf{solvent}}}{\mathbf{=}}\frac{{\mathbf{mol}}_{\mathbf{solvent}}}{\mathbf{\iota}\mathbf{\xb7}{\mathbf{mol}}_{\mathbf{solute}}\mathbf{+}{\mathbf{mol}}_{\mathbf{solvent}}}}$__

Moles of solute (urea):

$\mathbf{5}\mathbf{.}\mathbf{00}\mathbf{}\mathbf{g}\mathbf{}\overline{)\mathbf{urea}}\mathbf{\left(}\frac{\mathbf{1}\mathbf{}\mathbf{mol}\mathbf{}\mathbf{urea}}{\mathbf{60}\mathbf{.}\mathbf{06}\mathbf{}\mathbf{g}\mathbf{}\overline{)\mathbf{urea}}}\mathbf{\right)}\mathbf{=}$**0.083 moles**

Moles solvent (water):

Recall: **1 kg = 10 ^{3} g**

$\mathbf{0}\mathbf{.}\mathbf{100}\mathbf{}\overline{)\mathbf{kg}}\left(\frac{{10}^{3}\overline{)g}}{1\overline{)\mathrm{kg}}}\right)\left(\frac{1\mathrm{mol}{H}_{2}O}{18.016\overline{)g{H}_{2}O}}\right)\mathbf{=}$**5.55 moles**

A solution contains 5.00 g of urea, CO(NH_{2})_{2}, a nonvolatile compound, dissolved in 0.100 kg of water. If the vapor pressure of pure water at 25 °C is 23.7 torr, what is the vapor pressure of the solution?

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