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Ch.12 - Liquids, Solids & Intermolecular Forces
Tro - Chemistry: A Molecular Approach 6th Edition
Tro6th EditionChemistry: A Molecular ApproachISBN: 9780137832217Not the one you use?Change textbook
All textbooksTro 6th EditionCh.12 - Liquids, Solids & Intermolecular ForcesProblem 48b
Chapter 12, Problem 48b

In each pair of compounds, pick the one with the higher vapor pressure at a given temperature. Explain your reasoning. b. CH3CH2CH2OH or CH3OH

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Step 1: Understand that vapor pressure is a measure of the tendency of a substance to transition into the gas phase. It is influenced by the strength of the intermolecular forces within the substance. The weaker the intermolecular forces, the higher the vapor pressure.
Step 2: Identify the types of intermolecular forces in each compound. Both CH3CH2CH2OH (propanol) and CH3OH (methanol) are alcohols, and thus have hydrogen bonding, dipole-dipole interactions, and London dispersion forces.
Step 3: Compare the strength of the intermolecular forces in each compound. Both compounds have similar types of intermolecular forces, but propanol has a longer carbon chain, which increases the strength of its London dispersion forces.
Step 4: Recall that substances with stronger intermolecular forces have lower vapor pressures. Therefore, methanol, with its shorter carbon chain and weaker London dispersion forces, will have a higher vapor pressure than propanol.
Step 5: Conclude that CH3OH (methanol) has a higher vapor pressure at a given temperature than CH3CH2CH2OH (propanol) due to its weaker intermolecular forces.

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Key Concepts

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

Vapor Pressure

Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid or solid phase at a given temperature. It reflects the tendency of molecules to escape from the liquid phase into the gas phase. Compounds with weaker intermolecular forces generally exhibit higher vapor pressures because their molecules can more easily enter the vapor phase.
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Intermolecular Forces

Intermolecular forces are the forces of attraction or repulsion between neighboring particles (atoms, molecules, or ions). These forces include hydrogen bonding, dipole-dipole interactions, and London dispersion forces. Stronger intermolecular forces result in lower vapor pressures, as more energy is required for molecules to escape into the vapor phase.
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Hydrogen Bonding

Hydrogen bonding is a specific type of strong dipole-dipole interaction that occurs when hydrogen is bonded to highly electronegative atoms like oxygen, nitrogen, or fluorine. In the context of alcohols, such as CH3CH2CH2OH and CH3OH, hydrogen bonding significantly influences their physical properties, including vapor pressure. The presence of more hydrogen bonds typically leads to lower vapor pressure due to the increased energy required to break these interactions.
Related Practice
Textbook Question

Determine whether each pair of compounds forms a homogeneous solution when combined. For those that form homogeneous solutions, indicate the type of forces that are involved. a. CCl4 and H2O b. KCl and H2O c. Br2 and CCl4

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Textbook Question

In each pair of compounds, pick the one with the higher boiling point. Explain your reasoning. b. CH3OH or CH3SH

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Textbook Question

Determine whether each pair of compounds forms a homogeneous solution when combined. For those that form homogeneous solutions, indicate the type of forces that are involved. d. CH3CH2OH and H2O

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In each pair of compounds, pick the one with the higher vapor pressure at a given temperature. Explain your reasoning. a. CH4 or CH3Cl c. CH3OH or H2CO

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