Chloroform, CHCl3, a volatile liquid, was once used as an...

Chloroform, $\mathrm{CHCl}_{3}$, a volatile liquid, was once used as an anesthetic but has been replaced by safer compounds. Chloroform boils at $61.7^{\circ} \mathrm{C}$ and has a heat of vaporization of $31.4 \mathrm{~kJ} / \mathrm{mol}$. What is its vapor pressure at $37.2{ }^{\circ} \mathrm{C} ?$

Key Concepts

Vapor Pressure

Vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (liquid or solid) at a given temperature in a closed system. It is an important property that indicates how readily a substance evaporates, and it increases as temperature increases since more molecules have enough kinetic energy to escape the liquid phase.

Clausius-Clapeyron Equation

The Clausius-Clapeyron equation provides a way to quantify the relationship between the vapor pressure of a substance and temperature. This equation shows that the natural logarithm of the vapor pressure is inversely proportional to the temperature, taking into account the heat of vaporization. It is a useful tool for predicting how the vapor pressure changes with temperature under equilibrium conditions.

Heat of Vaporization

The heat of vaporization is the energy required to convert a given amount of a substance from a liquid into a vapor at a constant temperature, typically expressed per mole. It reflects the strength of the intermolecular forces within the liquid; higher values indicate stronger attractions and a higher energy requirement for the phase transition.

Transcript

00:02 Okay, so this question is about calculating of the vapor pressure.

00:08 Before we start, we have to review an equation that was taught in the class.

00:16 It's actually an equation that shows the relations between the vapor pressure and the temperature.

00:22 So the equation is like that.

00:25 So it tells you the logging vapor pressure, equals to minus the enthalpy or heat of the vaporization over rt plus b.

00:48 B is just a constant.

00:56 And this equation actually relates the vapor pressure and the temperature.

01:03 So if you look at the question, you will find ask you, right, the vapor pressure at certain temperatures.

01:08 So definitely we have to use this equation.

01:13 But the point is, we don't know the constant b.

01:18 That's a little bit hard.

01:19 But we can actually find two ways to actually eliminate b.

01:25 So let's read the question first.

01:27 It says chcl3 of volatile liquid.

01:34 We bore, so it will actually bore is ch3.

01:43 Sorry, it's chcl3, borse at 61 .7 degrees c.

01:56 So what this tells you? so we know for the bowling, as a boiling point, actually that point, the vapor pressure equals to the pressure of the atmosphere.

02:09 So here we can just write down p1, the vapor pressure, equals to 1 atm at 61 .7 degree c, which this is a t1.

02:29 This is the information we get.

02:33 And then it asks you what is the vaporization, what is the vapor pressure p2 at 37 .2 degre c.

02:49 Ask you that.

02:52 So we can actually try to write down the formula here.

02:57 That just plug in those symbols into this formula.

03:07 So we can write down first at t1, which equals 161 .7 degrees c.

03:21 The vapor pressure log p1 equals to the heat of the vaporization over, oh sorry, minus delta h, over the r times the temperature t1, and needs to plus b a constant.

03:51 And then add t2, which is equal to 37 .2 degrees c, we can again plug in the value, not value, the same.

04:03 Symbols, log in p2 equals to delta hv over rt2 plus b.

04:21 So the way we can get away or eliminate b is actually we just use 1 minus 2, right, this two equation, 1 minus 2.

04:32 So we can just do that, 1 minus 2.

04:36 And that equals to log in p1 minus log in p2 equals to minus delta h over r that 1 over t1 minus 1 over t2 so in this way we eliminate the b and now look at what we know we know the p1 we know the p2 we know the delta h, we know the t2.

05:12 We don't know the p2...

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