The vapor pressure of a volatile liquid can be determined by...

The vapor pressure of a volatile liquid can be determined by slowly bubbling a known volume of gas through it at a known temperature and pressure. In an experiment, 5.00 L of $\mathrm{N}_{2}$ gas is passed through 7.2146 $\mathrm{g}$ of liquid benzene $\left(\mathrm{C}_{6} \mathrm{H}_{6}\right)$ at $26.0^{\circ} \mathrm{C} .$ The liquid remaining after the experiment weighs 5.1493 g. Assuming that the gas becomes saturated with benzene vapor and that the total gas volume and temperature remain constant, what is the vapor pressure of the benzene in torr?

Key Concepts

Dalton's Law of Partial Pressures

Dalton's Law of Partial Pressures states that in a mixture of non-reacting gases, the total pressure is the sum of the partial pressures of each individual gas. This principle is key when analyzing a gas mixture that becomes saturated with vapor, as it helps isolate the vapor's contribution to the total pressure.

Ideal Gas Law

The Ideal Gas Law (PV = nRT) is a fundamental equation that relates the pressure, volume, number of moles, and temperature of a gas. It is used to calculate the moles of a vapor present in a gas mixture, allowing for the determination of partial pressures in experiments involving gas saturation with vapor.

Phase Equilibrium

Phase equilibrium refers to the condition under which the rates of evaporation and condensation are equal, resulting in a constant vapor pressure at a given temperature. This balance between the liquid and vapor phases is essential in understanding and measuring the vapor pressures of substances.

Vapor Pressure

Vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its liquid (or solid) phase at a given temperature in a closed system. It is a measure of a liquid's tendency to evaporate and is determined by the kinetic energy of the molecules and the intermolecular forces between them.

Transcript

00:03 Okay, let's see if we can figure out this problem.

00:06 We have a volatile liquid and we're told the vapor pressure can be determined by slowly bubbling a known volume of gas through it at a known temperature and pressure.

00:16 So we're given 5 liters of nitrogen is passed through a 7 .2146 gram sample of benzene at 26 degrees celsius.

00:25 The liquid remaining after the experiment has a mass of 5 .1493 grams.

00:30 We're going to assume the gas becomes saturated with benzene vapor and the total gas volume and temperature are constant.

00:38 We're asked to calculate the vapor pressure in torr.

00:44 So first of all, let's find the mass of benzene consumed in the reaction.

00:59 And that will equal 7 .2146 grams minus 5 .1493 grams.

01:09 7 .2146 minus 5 .1493, 2 .0653 grams is used.

01:25 Now let's convert that to moles.

01:30 2 .0653 grams of benzene, which is c6h6, 72, 78 point, i'm going to go to my molar mass calculator.

01:47 Do i have one open? i don't.

01:50 Hang on.

01:51 Lentech molar mass.

01:54 I think it's going to be 78 .12, 78 point, i wonder if benzene is in my list.

02:08 By golly it is.

02:10 This says 78 .11 but i'm going to use 78 .12 because that's what i would make my students use...

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