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Chapter 11: Problem 17

Explain in terms of intermolecular forces why (a) \(\mathrm{NH}_{3}\) has a higher boiling point than \(\mathrm{CH}_{4},\) and (b) \(\mathrm{KCl}\) has a higher melting point than \(\mathrm{I}_{2}\).

Short Answer

Expert verified
(a) \(\mathrm{NH}_{3}\) has a higher boiling point than \(\mathrm{CH}_{4}\) due to stronger hydrogen bonding and dipole-dipole forces. (b) \(\mathrm{KCl}\) has a higher melting point than \(\mathrm{I}_{2}\) due to stronger ionic bonding.

Step by step solution

01

Identify the Type of Intermolecular Forces in NH3 and CH4

Ammonia (\(\mathrm{NH}_{3}\)) has a polar covalent bond due to a significant difference in electronegativity between Nitrogen and Hydrogen atoms, leading to a presence of a dipole moment which results in dipole-dipole intermolecular forces. Additionally, \(\mathrm{NH}_{3}\) forms Hydrogen bonds due to the presence of Hydrogen which is bonded to Nitrogen which is more electronegative. Methane (\(\mathrm{CH}_4\)), however, has nonpolar covalent bonds as it consists of the same type of atoms (Hydrogen and Carbon) with similar electronegativities, leading to equal sharing of electrons, hence no polarity and only weak van der Waals forces (London dispersion forces) are present.
02

Interpret the Influence of Intermolecular Forces on NH3 and CH4 Boiling Points

The Hydrogen bonding and dipole-dipole forces in \(\mathrm{NH}_{3}\) are significantly stronger than the weak van der Waals forces in \(\mathrm{CH}_4\). It means, more energy would be required to break these forces resulting in a higher boiling point of \(\mathrm{NH}_{3}\) compared to \(\mathrm{CH}_4\).
03

Identify the Type of Intermolecular Forces in KCl and I2

Potassium Chloride (\(\mathrm{KCl}\)) is an ionic compound formed by the electrostatic interaction between positively charged Potassium and negatively charged Chlorine ions. The strong ionic bonds form a crystal lattice structure. On the other hand, Iodine (\(\mathrm{I}_{2}\)) is a molecular compound with nonpolar covalent bonds between Iodine atoms leading to van der Waals forces.
04

Interpret the Influence of Intermolecular Forces on KCl and I2 Melting Points

The ionic bonding in \(\mathrm{KCl}\) is incredibly strong and a higher temperature is required to overcome this bonding and disrupt the lattice, hence \(\mathrm{KCl}\) has a higher melting point than \(\mathrm{I}_{2}\), which only has weak van der Waals forces.

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Most popular questions from this chapter

A solid is very hard and has a high melting point. Neither the solid nor its melt conducts electricity. Classify the solid.

A student heated a beaker of cold water (on a tripod) with a Bunsen burner. When the gas is ignited, she noticed that there was water condensed on the outside of the beaker. Explain what happened.

What is a phase change? Name all possible changes that can occur among the vapor, liquid, and solid phases of a substance.

The following compounds, listed with their boiling points, are liquid at \(-10^{\circ} \mathrm{C}:\) butane, \(-0.5^{\circ} \mathrm{C} ;\) ethanol, \(78.3^{\circ} \mathrm{C} ;\) toluene, \(110.6^{\circ} \mathrm{C}\). At \(-10^{\circ} \mathrm{C},\) which of these liquids would you expect to have the highest vapor pressure? Which the lowest? Explain.

What is critical temperature? What is the significance of critical temperature in liquefaction of gases?
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