Choose from each pair the substance that, in the liquid state, would have the greater vapor pres

Choose from each pair the substance that, in the liquid...

Key Concepts

Hydrogen Bonding

Hydrogen bonding is a particularly strong type of dipole-dipole attraction that occurs when hydrogen is covalently bonded to highly electronegative atoms like oxygen, nitrogen, or fluorine. Its presence significantly reduces vapor pressure by creating strong cohesive forces between the molecules.

Dipole-Dipole Interactions

Dipole-dipole interactions occur in molecules with permanent dipoles, where the positive end of one molecule is attracted to the negative end of another. These forces are stronger than London dispersion forces and lead to lower vapor pressures by more effectively holding molecules together.

London Dispersion Forces

London dispersion forces are weak, temporary attractive forces that arise from momentary fluctuations in electron density in molecules. They are present in all substances but dominate in nonpolar molecules, and their strength increases with molecular size and mass, affecting vapor pressure accordingly.

Intermolecular Forces

Intermolecular forces are attractions between molecules, and they dictate many physical properties, including boiling point and vapor pressure. Stronger intermolecular forces result in lower vapor pressures because they bind the molecules more tightly in the liquid state.

Vapor Pressure

Vapor pressure is the measure of a liquid's tendency to evaporate by quantifying the pressure exerted by its vapor when in equilibrium with the liquid phase. It is inversely related to the strength of intermolecular forces; weaker forces allow molecules to escape more easily, leading to a higher vapor pressure.

Transcript

00:01 In this question we are comparing the effect of intermolecular forces on vapor pressure.

00:07 Vapor pressure versus intermolecular forces.

00:16 Remember, vapor pressure defines the boiling point because if liquid only boils when its vapor pressure is equal to the atmospheric pressure surrounding that liquid.

00:28 So, for us to determine the effect of intermolecular forces, on vapor pressure it means if the intermolecular forces are weak forces equal to high the vapor pressure because an increase let's use a decrease in the strength of forces equals an increase in the ease of evaporation and if a liquid is easily evaporated it means there is a higher vapor pressure.

01:10 So moving on, this is basically what we'll be looking at.

01:13 We look at the strength of the intermolecular forces that are prevailing.

01:18 The stronger the force, the lower the rate of evaporation means the lower the vapor pressure.

01:26 So moving at the first set, a, we've been given b -i -c -l -3 and b -i -c -l -3.

01:40 We are throwing.

01:42 When we are looking at this, these are non -polar compounds.

01:48 Nanopolar compounds.

01:51 As a result, the intermolecular forces that are dominant here are the dispassion forces.

02:02 So for both compounds, dominant intermolecular forces are the dispassion forces.

02:11 And we know that what then differentiates the strength of the molecular forces, of the intermolecular forces is the size of molecules the higher the size or the bigger the size equal to the higher the strength of the forces so when we look at these two we can tell that b i pr3 is bigger than b i c alp3 so it is easier it is much easier to evaporate b i c l3 than it is to evaporate b -i -pr -3.

02:52 As a result, b -i -c -o -3 has got a higher vapor pressure.

02:58 B -i -c -o -3 has got a higher vapor pressure than b -i -p -o -3.

03:03 So just to go through that again briefly, because this is the same principle that we're going to be using for the remaining molecules or sets.

03:11 We look at the intermolecular forces that i had play.

03:15 For this one, we've been given b -i -c -l -3 and b -i -pr -3.

03:20 And both of these are non -polar compounds and for non -polar compounds the most dominant intermolecular force are the dispassion forces.

03:30 So they are at power.

03:32 They are equal when it comes to the dominant intermolecular forces.

03:36 But what then differentiates them is the size of the molecules.

03:40 B .i.

03:41 P .r.

03:41 3 has got bigger molecules than b .c .o .3.