Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 11: Problem 79

Ethylene glycol \(\left(\mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{OH}\right)\) is the major component of antifreeze. It is a slightly viscous liquid, not very volatile at room temperature, with a boiling point of \(198^{\circ} \mathrm{C}\). Pentane \(\left(\mathrm{C}_{5} \mathrm{H}_{12}\right),\) which has about the same molecular weight, is a nonviscous liquid that is highly volatile at room temperature and whose boiling point is \(36.1^{\circ} \mathrm{C}\). Explain the differences in the physical properties of the two substances.

Short Answer

Expert verified
The differences in physical properties of ethylene glycol (HOCH2CH2OH) and pentane (C5H12) stem from their molecular structures and the resulting intermolecular forces. Ethylene glycol's polar hydroxyl groups lead to strong hydrogen bonding, making it more viscous, less volatile, and resulting in a higher boiling point of 198°C. Pentane, on the other hand, interacts via weaker dispersion forces and has no functional groups, leading to a less viscous liquid, higher volatility, and a boiling point of 36.1°C.

Step by step solution

01

1. Molecular structure and intermolecular forces for ethylene glycol

Ethylene glycol is an organic compound with the molecular formula HOCH2CH2OH. The molecule contains two hydroxyl groups (-OH), which make it an alcohol. The presence of these polar hydroxyl groups gives rise to strong intermolecular hydrogen bonding between ethylene glycol molecules.
02

2. Molecular structure and intermolecular forces for pentane

Pentane, on the other hand, is an alkane with the molecular formula C5H12. It is a simple, non-polar hydrocarbon with no functional groups, which results in weaker dispersion forces (also known as London dispersion forces or van der Waals forces) acting between pentane molecules.
03

3. Viscosity comparison

Viscosity depends mainly on the strength of intermolecular forces in a substance. Ethylene glycol has strong hydrogen bonding between its molecules due to the presence of hydroxyl groups, which makes it more viscous than pentane. In contrast, pentane molecules experience weaker dispersion forces, making it a less viscous liquid.
04

4. Volatility comparison

Volatility is directly related to the strength of intermolecular forces in a substance. A more volatile substance has weaker intermolecular forces, allowing molecules to escape from the liquid phase more easily. Since ethylene glycol experiences strong intermolecular hydrogen bonding, it is less volatile at room temperature compared to pentane, which has weaker dispersion forces.
05

5. Boiling point comparison

Boiling point is also influenced by the strength of intermolecular forces. Substances with stronger intermolecular forces require more energy to overcome these forces and transition from the liquid to the gas phase. This is why ethylene glycol, with its strong hydrogen bonding, has a higher boiling point at 198°C, while pentane, with its weaker dispersion forces, has a boiling point of only 36.1°C.
06

Conclusion

The physical properties of ethylene glycol and pentane can be explained by the differences in their molecular structures and the resulting intermolecular forces. Ethylene glycol, with its polar hydroxyl groups, experiences strong hydrogen bonding, leading to a more viscous, less volatile liquid with a higher boiling point than pentane, which interacts via weaker dispersion forces and has no functional groups.

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!

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

The vapor pressure of a volatile liquid can be determined by slowly bubbling a known volume of gas through it at a known temperature and pressure. In an experiment, \(5.00 \mathrm{~L}\) of \(\mathrm{N}_{2}\) gas is passed through \(7.2146 \mathrm{~g}\) of liquid benzene, \(\mathrm{C}_{6} \mathrm{H}_{6}\), at \(26.0{ }^{\circ} \mathrm{C}\). The liquid remaining after the experiment weighs \(5.1493 \mathrm{~g}\). Assuming that the gas becomes saturated with benzene vapor and that the total gas volume and temperature remain constant, what is the vapor pressure of the benzene in torr?

(a) How does the average kinetic energy of molecules compare with the average energy of attraction between molecules in solids, liquids, and gases? (b) Why does increasing the temperature cause a solid substance to change in succession from a solid to a liquid to a gas? (c) What happens to a gas if you put it under extremely high pressure?

A watch with a liquid crystal display (LCD) does not function properly when it is exposed to low temperatures during a trip to Antarctica. Explain why the LCD might not function well at low temperature.

Name the phase transition in each of the following situations and indicate whether it is exothermic or endothermic: (a) When ice is heated, it turns to water. (b) Wet clothes dry on a warm summer day. (c) Frost appears on a window on a cold winter day. (d) Droplets of water appear on a cold glass of beer.

(a) Two pans of water are on different burners of a stove. One pan of water is boiling vigorously, while the other is boiling gently. What can be said about the temperature of the water in the two pans? (b) A large container of water and a small one are at the same temperature. What can be said about the relative vapor pressures of the water in the containers?
See all solutions

Recommended explanations on Chemistry Textbooks

Organic Chemistry

Read Explanation

Physical Chemistry

Read Explanation

The Earths Atmosphere

Read Explanation

Chemical Reactions

Read Explanation

Chemical Analysis

Read Explanation

Kinetics

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