Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 5: Problem 51

Account for the following observations in terms of the type and strength of intermolecular forces. (a) The melting point of xenon is \(-112^{\circ} \mathrm{C}\) and that of argon is \(-189^{\circ} \mathrm{C}\). (b) The vapor pressure of diethyl ether \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OC}_{2} \mathrm{H}_{3}\right)\) is greater than that of water. (c) The boiling point of pentane, \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{3} \mathrm{CH}_{3}\), is \(36.1^{\circ} \mathrm{C}\), whereas that of 2,2 -dimethylpropane (also known as neopentane) is \(9.5^{\circ} \mathrm{C}\).

Short Answer

Expert verified
Xenon melts at a higher temperature than argon due to larger atomic size and stronger dispersion forces. Diethyl ether has a higher vapor pressure than water due to the absence of strong hydrogen bonds. Pentane boils at a higher temperature than neopentane due to greater surface area and stronger dispersion forces.

Step by step solution

01

Compare Melting Points of Xenon and Argon

Consider the periodic table and the positions of xenon (Xe) and argon (Ar). Both Xe and Ar are noble gases and exist as monatomic gases; they are held together by weak dispersion forces (Van der Waals forces). The melting points of noble gases usually increase with increases in atomic size and mass because larger atoms have more electrons, which can lead to stronger dispersion forces. Xenon is heavier and has more electrons than argon, hence the intermolecular forces are stronger in xenon, requiring more energy (higher temperature) to overcome them compared to argon. This is the reason why the melting point of Xe is higher (less negative) than Ar.
02

Explain Vapor Pressure Differences Between Diethyl Ether and Water

Consider the types of intermolecular forces present in diethyl ether \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OC}_{2} \mathrm{H}_{5}\) and water (H2O). Diethyl ether has dispersion and dipole-dipole forces but lacks hydrogen bonding, which is present in water. Hydrogen bonding is significantly stronger than other dipole-dipole interactions. Because of the absence of strong hydrogen bonding in diethyl ether, it requires less energy to vaporize it, and thus it has a higher vapor pressure than water at the same temperature.
03

Analyze Boiling Points of Pentane and Neopentane

Consider the molecular structures and surface areas of pentane \(\mathrm{CH}_{3} \left(\mathrm{CH}_{2}\right)_{3} \mathrm{CH}_{3}\) and neopentane \((\mathrm{C}(\mathrm{CH}_3)_4)\). Both molecules are nonpolar and interact through dispersion forces. Pentane has a linear structure, which allows for more surface area contact between molecules, leading to stronger dispersion forces compared to neopentane, which has a more compact, spherical shape. This results in weaker dispersion forces. Thus, it takes more energy (higher temperature) to overcome the intermolecular forces in pentane, leading to a higher boiling point than neopentane.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Melting Point
The melting point of a substance is the temperature at which it changes from a solid to a liquid. This process requires enough energy to overcome the intermolecular forces that hold the particles together in the solid state.

For noble gases like xenon and argon, which both exist as monatomic gases in their solid forms, the melting points are influenced by the strength of dispersion forces among their atoms. A higher atomic mass and size tend to increase these forces due to a larger number of electrons, leading to a higher melting point. That's why xenon, with more electrons and a larger atomic mass compared to argon, has the higher melting point.
Vapor Pressure
Vapor pressure is the measure of a liquid's tendency to evaporate. It indicates how often molecules in the liquid escape into the gas phase at a given temperature. Substances with higher vapor pressures evaporate more readily.

In the case of diethyl ether versus water, diethyl ether has a higher vapor pressure because it lacks hydrogen bonding, which is present in water. Without strong hydrogen bonds, the molecules in diethyl ether require less energy to break apart and enter into the gas phase, making its vapor pressure greater than that of water.
Boiling Point
The boiling point is the temperature at which a liquid's vapor pressure equals the surrounding pressure, causing it to turn to gas. The boiling point can provide insights into the intermolecular forces within a substance. Stronger intermolecular forces typically result in higher boiling points.

For example, pentane has a higher boiling point than neopentane due to its extended structure increasing surface area, which enhances the dispersion forces. Neopentane's more compact shape results in weaker dispersion forces and consequently, a lower boiling point.
Van der Waals Forces
Van der Waals forces encompass a variety of intermolecular attractions, including dispersion forces and dipole-dipole interactions. These forces are weaker than chemical bonds, but they are crucial in determining the physical properties of substances.

In noble gases, the primary Van der Waals force at work is the dispersion force, which arises from fluctuations in electron distribution that lead to temporary dipole moments. Larger atoms have a greater potential for stronger dispersion forces because of their increased number of electrons.
Hydrogen Bonding
Hydrogen bonding is a specific, strong type of dipole-dipole interaction that occurs when hydrogen is bound to a highly electronegative atom, such as oxygen or nitrogen. The resulting polarity creates an intense attraction between molecules.

This powerful intermolecular force is the reason why water has a relatively high boiling point and lower vapor pressure compared to many other molecules of similar size that do not exhibit hydrogen bonding.
Dispersion Forces
Dispersion forces, also known as London dispersion forces, are weak intermolecular forces that arise in all atoms and molecules regardless of their polarity. These forces are the result of temporary instantaneous dipoles and induced dipoles.

The strength of dispersion forces increases with molecular size and the number of electrons. Substances with higher molecular weights and larger surface areas, such as xenon and pentane, will typically have stronger dispersion forces which affect their melting and boiling points.

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

Name two compounds that exist as network solids at room temperature and pressure.

Explain why ionic solids like \(\mathrm{NaCl}\) have high melting points yet dissolve readily in water, whereas network solids like diamond have very high melting points and do not dissolve.

For which of the following molecules and ions will dipole-dipole interactions be important: (a) \(\mathrm{SF}_{4}\); (b) \(\mathrm{PF}_{5} ;\) (c) \(\mathrm{PF}_{3} ;\) (d) \(\mathrm{SF}_{4}\) ?

A commonly occurring mineral has a cubic unit cell in which the metal cations \(\mathrm{M}\) occupy the comers and face centers. Inside the unit cell, there are anions \(\mathrm{A}\) that occupy all the tetrahedral holes created by the cations. What is the chemical formula of the \(M_{x} A_{y}\) compound?

For which of the following molecules will dipoledipole interactions be important: (a) \(\mathrm{CH}_{4} ;\) (b) \(\mathrm{CH}_{3} \mathrm{Cl}\); (c) \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\); (d) \(\mathrm{CHCl}_{3}\); (e) \(\mathrm{CCl}_{4}\) ?
See all solutions

Recommended explanations on Chemistry Textbooks

Chemistry Branches

Read Explanation

Kinetics

Read Explanation

Physical Chemistry

Read Explanation

Nuclear Chemistry

Read Explanation

Chemical Reactions

Read Explanation

Chemical Analysis

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free