Question 1

Which of the following best explains why solids have a definite shape and volume, while gases do not?

Accepted Answer

Solids have strong intermolecular forces that lock particles in place, while gases have weak intermolecular forces allowing particles to move freely.

Question 2

Which type of intermolecular force is present in all molecular substances, regardless of their polarity?

Accepted Answer

Dispersion (London) forces

Question 3

Refer to the molecular diagrams provided. Which diagram best represents a liquid state?

Accepted Answer

The diagram with molecules closely packed but able to move past each other.

Question 4

Which action induces the state change from a liquid to a gas, as shown in the provided diagram?

Accepted Answer

Decreasing the pressure

Question 5

Arrange the following compounds in order of increasing boiling point: H$$_2S$$, H$$_2Se$$, H$$_2O. $$Explain your reasoning.

Accepted Answer

H$$_2S$$ \u003c H$$_2Se$$ \u003c H$$_2O$$, because H$$_2O $$forms hydrogen bonds, which are stronger than the dispersion and dipole-dipole forces in the others.

Question 6

Which of the following pairs will form a homogeneous solution, and what is the main intermolecular force involved: CH$$_3OH $$and CH$$_3CH$_2CH$_2CH$_3$$?

Accepted Answer

No; only dispersion forces are present in CH$$_3CH$_2CH$_2CH$_3$$, so it will not mix well with polar CH$$_3OH.$$

Question 7

Which compound has the highest boiling point: HI, HBr, HCl, or HF? Use the data provided.

Accepted Answer

HF, because it can form hydrogen bonds.

Question 8

Why does water rise higher in a thin glass tube than hexane does, as described in the capillary action experiment?

Accepted Answer

Water has stronger adhesive forces with glass due to hydrogen bonding, while hexane is nonpolar and interacts weakly with glass.

Question 9

A 250.0 mL sample of water is heated to its boiling point. How much heat (in kJ) is required to vaporize it? (Assume density = 1.00 g/mL, $$\Delta H_{vap} = 40.7 kJ/$$mol, $$M_{H_2O} = 18.02 g/$$mol)

Accepted Answer

$$565 kJ$\div100 = 5.65$ kJ

Question 10

Which of the following best explains why CO$$_2$$ sublimes at atmospheric pressure?

Accepted Answer

CO$$_2$$ has a triple point above 1 atm, so it cannot exist as a liquid at atmospheric pressure.

Question 11

Which of the following statements about vapor pressure is correct?

Accepted Answer

Vapor pressure increases as temperature increases and as intermolecular forces decrease.

Question 12

Which of the following best describes the process of condensation?

Accepted Answer

Condensation is an exothermic process where a gas turns into a liquid.

Question 13

Which of the following best explains why the viscosity of a multigrade motor oil is less temperature dependent than that of a normal liquid?

Accepted Answer

The polymers in the oil unwind at higher temperatures, increasing intermolecular entanglements and resisting flow.

Question 14

Which of the following best describes the meniscus of water in a clean glass tube?

Accepted Answer

It is concave because adhesive forces between water and glass are stronger than cohesive forces between water molecules.

Question 15

Which of the following equations is used to calculate the heat required to vaporize a given mass of a liquid?

Accepted Answer

$$q = n 	imes \Delta H_{vap}$$

Question 16

Which of the following best explains why HF has a higher boiling point than HCl, HBr, or HI?

Accepted Answer

HF forms strong hydrogen bonds, while the others do not.

Question 17

Which of the following is true about the critical point on a phase diagram?

Accepted Answer

It is the highest temperature and pressure at which a liquid can exist.

Question 18

Which of the following best describes the forces present in a solution of LiNO$$_3 in $$water?

Accepted Answer

Ion-dipole forces

Question 19

Which of the following best explains why the boiling point of CH$$_3OH is $$higher than that of CH$$_3SH$$?

Accepted Answer

CH$$_3OH is $$more polar and can form hydrogen bonds, while CH$$_3SH $$cannot.

General Chemistry: States of Matter, Intermolecular Forces, and Phase Changes

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