Ch.11 - Liquids and Intermolecular Forces

Problem 18b

Chapter 11, Problem 18b

(b) Which of these kinds of interactions are broken when a liquid is converted to a gas?

Verified step by step guidance

Identify the state change involved: The problem states that a liquid is converted to a gas, which is the process of vaporization.

Understand the types of interactions in liquids: In liquids, molecules are held together by intermolecular forces. These include hydrogen bonds, dipole-dipole interactions, and London dispersion forces.

Recognize the effect of vaporization on intermolecular forces: When a liquid turns into a gas, the molecules must overcome the intermolecular forces that hold them together in the liquid state.

Determine which interactions are affected: During vaporization, all types of intermolecular forces (hydrogen bonds, dipole-dipole interactions, and London dispersion forces) are broken to allow the molecules to move freely and form a gas.

Conclude the specific interactions broken: Thus, when a liquid is converted to a gas, hydrogen bonds, dipole-dipole interactions, and London dispersion forces are the kinds of interactions that are broken.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Intermolecular Forces

Intermolecular forces are the attractive forces between molecules that influence the physical properties of substances. In liquids, these forces, such as hydrogen bonds, dipole-dipole interactions, and London dispersion forces, hold the molecules close together. When a liquid is converted to a gas, these forces must be overcome, allowing the molecules to move freely and occupy a larger volume.

Phase Change

A phase change refers to the transition of a substance from one state of matter to another, such as from liquid to gas. This process involves energy changes, specifically the absorption of heat, which provides the energy needed to break intermolecular forces. Understanding phase changes is crucial for grasping how temperature and pressure affect the state of a substance.

Vaporization

Vaporization is the process by which a liquid turns into a gas, occurring through two main mechanisms: evaporation and boiling. During vaporization, molecules at the surface of the liquid gain enough energy to overcome intermolecular forces and escape into the gas phase. This concept is essential for understanding how temperature and pressure influence the transition from liquid to gas.

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Related Practice

Textbook Question

(a) Which type of intermolecular attractive force operates between all molecules?

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Textbook Question

(b) Which type of intermolecular attractive force operates only between polar molecules?

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Textbook Question

(c) Which type of intermolecular attractive force operates only between the hydrogen atom of a polar bond and a nearby small electronegative atom?

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Textbook Question

Describe the intermolecular forces that must be overcome to convert these substances from a liquid to a gas: (a) SO₂, (b) CH₃COOH, (c) H₂S.

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Textbook Question

Which type of intermolecular force accounts for each of these differences? (a) CH₃OH boils at 65 °C; CH₃SH boils at 6 °C. (d) Acetone boils at 56 °C, whereas 2-methylpropane boils at -12 °C.

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Textbook Question

Which type of intermolecular force accounts for each of these differences? (b) Xe is a liquid at atmospheric pressure and 120 K, whereas Ar is a gas under the same conditions. (c) Kr, atomic weight 84 amu, boils at 120.9 K, whereas Cl₂, molecular weight about 71 amu, boils at 238 K.

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