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Ch.11 - Liquids & Phase Changes
McMurry - Chemistry 8th Edition
McMurry8th EditionChemistryISBN: 9781292336145Not the one you use?Change textbook
All textbooksMcMurry 8th EditionCh.11 - Liquids & Phase ChangesProblem 37
Chapter 11, Problem 37

Two dichloroethylene molecules with the same chemical formula1C2H2Cl22, but different arrangements of atoms are shown.Cis and trans isomers of dichloroethylene, illustrating different atomic arrangements.
(c) Which form of dichloroethylene has the highest boiling point?

Verified step by step guidance
1
Identify the two isomers of dichloroethylene: cis and trans.
Understand that the cis isomer has both chlorine atoms on the same side of the double bond, while the trans isomer has the chlorine atoms on opposite sides.
Recall that the boiling point of a molecule is influenced by its intermolecular forces, such as dipole-dipole interactions and van der Waals forces.
Recognize that the cis isomer has a higher dipole moment due to the polar chlorines being on the same side, leading to stronger dipole-dipole interactions.
Conclude that the cis isomer of dichloroethylene will have a higher boiling point than the trans isomer due to these stronger intermolecular forces.

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Key Concepts

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

Isomerism

Isomerism refers to the phenomenon where two or more compounds have the same molecular formula but different structural arrangements of atoms. In the case of dichloroethylene, the two isomers, cis and trans, differ in the spatial orientation of the chlorine atoms around the double bond, leading to distinct physical and chemical properties.
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Boiling Point

The boiling point of a substance is the temperature at which its vapor pressure equals the external pressure, causing it to change from liquid to gas. Factors influencing boiling points include molecular weight, intermolecular forces, and molecular structure. Generally, isomers with stronger intermolecular forces, such as dipole-dipole interactions, will have higher boiling points.
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Intermolecular Forces

Intermolecular forces are the forces of attraction or repulsion between neighboring particles (atoms, molecules, or ions). In dichloroethylene, the cis isomer has a higher dipole moment due to the arrangement of chlorine atoms, leading to stronger dipole-dipole interactions compared to the trans isomer, which can result in a higher boiling point for the cis form.
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Related Practice
Textbook Question
Choose any two temperatures and corresponding vapor pressures in the table given in Problem 11.30, and use those values to calculate ΔHvap for dichloromethane in kJ/mol. How does the value you calculated compare to the value you read from your plot in Problem 11.32?
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Textbook Question
The dipole moment of methanol is m = 1.70 D. Use arrowsto indicate the direction in which electrons are displaced.

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Textbook Question
Dichlorodifluoromethane, CCl2F2, one of the chlorofluo- rocarbon refrigerants responsible for destroying part of the Earth's ozone layer, has Pvap = 40.0 mm Hg at -81.6 °C and Pvap = 400 mm Hg at -43.9 °C. What is the normal boiling point of CCl2F2 in °C?
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Textbook Question
Why is the heat of sublimation, ΔHsubl, equal to the sum of ΔHvap and ΔHfusion at the same temperature?
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Textbook Question

Naphthalene, better known as 'mothballs,' has bp = 218 °C and ΔHvap = 43.3 kJ>mol. What is the entropy of vaporization, ΔSvap in J/(K mol) for naphthalene?

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Textbook Question
Mercury has mp = -38.8 °C and bp = 356.6 °C. What,if any, phase changes take place under the following condi-tions at 1.0 atm pressure? (a) The temperature of a sample is raised from -30 °C to 365 °C.
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