Arrange the following compounds in order of increasing boiling point: RbF, CO_2,
ID: 531115 • Letter: A
Question
Arrange the following compounds in order of increasing boiling point: RbF, CO_2, CH_3OH, CH_3Br. Explain the arrangement. Which member of each of these pairs of substances would you expect to have a higher boiling point: O_2 or N_2, SO_2 or CO_2, HF or HI? Predict which of these liquids has the greater surface tension: ethanol (C_2H_5OH) or dimethyl ether (CH_3OCH_3). What is the equilibrium vapor pressure of a liquid? How does it change with temperature? Why is solid carbon dioxide called dry ice? Which of these indicates very strong intermolecular forces in a liquid: (a) a very low surface tension, (b) a very low critical temperature, (c) a very low boiling point, (d) a very low vapor pressure?Explanation / Answer
1) CO2 < CH3Br < CH3OH < RbF.
The least boiling point {CO2 }.
Highest boiling point {RbF}.This order is attributed to the intermolecular force between each molecule.
CO2- dispersion forces
CH3BrCHX3Br - dispersion and dipole-dipole
CH3OHCHX3OH - dispersion, dipole-dipole, and hydrogen bonding
RbFRbF - ionic {also it's a salt and generally salts possess high boiling point .
2)
a) O2 possess higher boiling point than N2. This is because it has more electrons. Because of the higher number of electrons, it has higher dispersion forces (attractive forces). This means that more energy (heat) is required to unstick the molecules into a different state of matter.
b) SO2 posses higher boiling point than CO2.This is because SO2 has a higher molecular mass than CO2, also SO2 is a polar molecule and CO2 not as a polar molecule as SO2 .Hence SO2 can form more effective dipole-dipole interactios, these increase the boiling point.
c) HF possess higher boiling point than HI.
Although HI molecules contain more electrons than HF, there are increased van der Waals forces in HI. But HF has a higher boiling point than HI because of hydrogen bonding.
3)
C2H5OH possess higher surface tension than diethyl ether.The attractive forces between the ethanol molecules are much greater due to hydrogen bonding, thus the surface ethanol molecules pulled inward even more by the deeper inside molecules. This leads to ethanol having a higher surface tension than dimethyl ether, which is non polar (and thus do not attract to each other as much).
4)
Vapor pressure or equilibrium vapor pressure is defined as the pressureexerted by a vapor in thermodynamicequilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system.
5)
When temperature increases K.E of molecules increases.So intermolecular forces break up and molecules easily leave the surface.Thus vapor pressure of liquid increases with rise of temperature.
6)
Answer) (d) very low vapour pressure.
Very strong intermolecular force of attraction means greater energy required to change in to vapor phase, hence lower vapor pressure.
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