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Chapter 11: Problem 73

As the intermolecular attractive forces between molecules increase in magnitude, do you expect each of the following to increase or decrease in magnitude? (a) Vapor pressure, (b) heat of vaporization, (c) boiling point, (d) freezing point, (e) viscosity, (f) surface tension, ( g) critical temperature.

Short Answer

Expert verified
As the intermolecular attractive forces between molecules increase in magnitude, we expect: (a) Vapor pressure to decrease, (b) Heat of vaporization to increase, (c) Boiling point to increase, (d) Freezing point to increase, (e) Viscosity to increase, (f) Surface tension to increase, and (g) Critical temperature to increase.

Step by step solution

01

(a) Vapor pressure

As intermolecular attractive forces increase, the ability of molecules to escape the liquid phase and enter the gas phase decreases due to stronger interactions between molecules. This leads to a lower equilibrium vapor pressure above the liquid, because fewer molecules have the energy to escape the liquid phase. So, as intermolecular attractive forces increase, we expect the vapor pressure to decrease in magnitude.
02

(b) Heat of vaporization

Heat of vaporization is the amount of energy required to convert a liquid into a vapor at constant temperature and pressure. When intermolecular attractive forces are stronger, more energy is needed to overcome these forces and separate the molecules from each other as they transition from the liquid to the gas phase. Thus, we expect the heat of vaporization to increase in magnitude as intermolecular attractive forces increase.
03

(c) Boiling point

Boiling point is the temperature at which a substance's vapor pressure equals the external atmospheric pressure, and the liquid starts turning into a gas. If the vapor pressure of a substance decreases with stronger intermolecular attractive forces (as we determined in part (a)), then the temperature must be raised to reach the atmospheric pressure, meaning the boiling point will also increase. So, we expect the boiling point to increase in magnitude as intermolecular attractive forces increase.
04

(d) Freezing point

As the intermolecular attractive forces increase, molecules tend to stick together more, which makes it easier for them to form a solid structure. This means that freezing may occur at higher temperatures when intermolecular forces are stronger because less energy needs to be removed from the system to form a solid. Therefore, we expect the freezing point to increase in magnitude as intermolecular attractive forces increase.
05

(e) Viscosity

Viscosity is the resistance of a liquid to flow. When intermolecular attractive forces are stronger, molecules stick together more, making it harder for them to slide past each other. This results in a higher resistance to flow or an increased viscosity. So, we expect the viscosity to increase in magnitude as intermolecular attractive forces increase.
06

(f) Surface tension

Surface tension is the energy required to increase the surface area of a liquid. When intermolecular attractive forces are stronger, the molecules at the surface of the liquid are held together more tightly, meaning they are harder to separate and require more energy to increase the surface area. Therefore, we expect the surface tension to increase in magnitude as intermolecular attractive forces increase.
07

(g) Critical temperature

Critical temperature is the temperature above which a gas cannot be liquefied regardless of how much pressure is applied. When intermolecular attractive forces are stronger, it becomes harder for the gas molecules to be separated from each other, allowing liquefaction at higher temperatures. Thus, we expect the critical temperature to increase in magnitude as intermolecular attractive forces increase.

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Most popular questions from this chapter

True or false: (a) \(\mathrm{CBr}_{4}\) is more volatile than \(\mathrm{CCl}_{4} .(\mathbf{b}) \mathrm{CBr}_{4}\) has a higher boiling point than \(\mathrm{CCl}_{4}\) . (c) CBr. has weaker intermolecular forces than \(\mathrm{CCl}_{4}\) . (d) \(\mathrm{CBr}_{4}\) has a higher vapor pressure at the same temperature than \(\mathrm{CCl}_{4}\) .

Based on the type or types of intermolecular forces, predict the substance in each pair that has the higher boiling point:(a) propane \(\left(\mathrm{C}_{3} \mathrm{H}_{8}\right)\) or \(n\) -butane \(\left(\mathrm{C}_{4} \mathrm{H}_{10}\right),(\mathbf{b})\) diethyl ether \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OCH}_{2} \mathrm{CH}_{3}\right)\) or 1 -butanol \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\right)\) (c) sulfur dioxide \(\left(\mathrm{SO}_{2}\right)\) or sulfur trioxide \(\left(\mathrm{SO}_{3}\right),(\mathbf{d})\) phosgene \(\left(\mathrm{Cl}_{2} \mathrm{CO}\right)\) or formaldehyde \(\left(\mathrm{H}_{2} \mathrm{CO}\right)\)

True or false: (a) For molecules with similar molecular weights, the dispersion forces become stronger as the molecules become more polarizable. (b) For the noble gases the dispersion forces decrease while the boiling points increase as you go down the column in the periodic table. (c) In terms of the total attractive forces for a given substance, dipole- dipole interactions, when present, are always greater than dispersion forces.( \(\mathbf{d}\) ) All other factors being the same, dispersion forces between linear molecules are greater than those between molecules whose shapes are nearly spherical. (e) The larger the atom, the more polarizable it is.

Ethanol \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)\) melts at \(-114^{\circ} \mathrm{C}\) and boils at \(78^{\circ} \mathrm{C}\) . The enthalpy of fusion of ethanol is \(5.02 \mathrm{kJ} / \mathrm{mol},\) and its enthalpy of vaporization is 38.56 \(\mathrm{kJ} / \mathrm{mol}\) . The specific heats of solid and liquid ethanol are 0.97 and \(2.3 \mathrm{J} / \mathrm{g}-\mathrm{K},\) respectively. (a) How much heat is required to convert 42.0 \(\mathrm{g}\) of ethanol at \(35^{\circ} \mathrm{C}\) to the vapor phase at \(78^{\circ} \mathrm{C} ?(\mathbf{b})\) How much heat is required to convert the same amount of ethanol at \(-155^{\circ} \mathrm{C}\) to the vapor phase at \(78^{\circ} \mathrm{C} ?\)

Ethyl chloride \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}\right)\) boils at \(12^{\circ} \mathrm{C}\) . When liquid \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}\) under pressure is sprayed on a room-temperature \(\left(25^{\circ} \mathrm{C}\right)\) surface in air, the surface is cooled considerably. (a) What does this observation tell us about the specific heat of \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}(g)\) as compared with that of \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}(l) ?\) Assume that the heat lost by the surface is gained by ethyl chloride. What enthalpies must you consider if you were to calculate the final temperature of the surface?
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