Question

True or false: (a) \(\mathrm{CBr}_{4}\) is more volatile than \(\mathrm{CCl}_{4}\). (b) \(\mathrm{CBr}_{4}\) has a higher boiling point than \(\mathrm{CCl}_{4}\). (c) \(\mathrm{CBr}_{4}\) has weaker intermolecular forces than \(\mathrm{CCl}_{4}\). (d) \(\mathrm{CBr}_{4}\) has a higher vapor pressure at the same temperature than \(\mathrm{CCl}_{4}\)

Short answer

(a) False (b) True (c) False (d) False

Step-by-step solution

Understanding Volatility

Volatility is the ability of a substance to evaporate or turn into a vapor at a given temperature. In general, substances with weaker intermolecular forces tend to have higher volatility as less energy is required to separate the molecules. To determine whether \(\mathrm{CBr}_{4}\) is more volatile than \(\mathrm{CCl}_{4}\), we need to compare their intermolecular forces.

Comparing Intermolecular Forces

The dominant intermolecular forces between \(\mathrm{CBr}_{4}\) and \(\mathrm{CCl}_{4}\) are London Dispersion Forces (LDF), which are temporary attractive forces that result from the constant motion of electrons. LDFs are stronger in molecules with more electrons, as they have larger electron clouds which can create stronger temporary dipoles. Since bromine has more electrons than chlorine, \(\mathrm{CBr}_{4}\) has stronger LDFs than \(\mathrm{CCl}_{4}\).

Answering Statement (a)

Since \(\mathrm{CBr}_{4}\) has stronger LDFs than \(\mathrm{CCl}_{4}\), it will require more energy to separate the molecules and is therefore less volatile. Statement (a) is false.

Understanding Boiling Points

The boiling point of a substance is the temperature at which its vapor pressure equals atmospheric pressure. In general, substances with stronger intermolecular forces have higher boiling points, as more energy is required to separate the molecules and overcome the attractive forces.

Answering Statement (b)

Since \(\mathrm{CBr}_{4}\) has stronger LDFs than \(\mathrm{CCl}_{4}\), it will have a higher boiling point. Statement (b) is true.

Answering Statement (c)

We already established that \(\mathrm{CBr}_{4}\) has stronger LDFs than \(\mathrm{CCl}_{4}\). Statement (c) is false.

Understanding Vapor Pressure

Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid phase at a given temperature. Substances with higher volatility have higher vapor pressures, as they evaporate more readily.

Answering Statement (d)

Since \(\mathrm{CBr}_{4}\) is less volatile than \(\mathrm{CCl}_{4}\) due to its stronger LDFs, it will have a lower vapor pressure at the same temperature. Statement (d) is false.