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

(a) Determine the volatility of \(\mathrm{CBr}_{4}\) and \(\mathrm{CCl}_{4}\)

Volatility is the tendency of a substance to vaporize. Molecules with weaker intermolecular forces tend to be more volatile than those with stronger intermolecular forces. The intermolecular forces present in both \(\mathrm{CBr}_{4}\) and \(\mathrm{CCl}_{4}\) are London dispersion forces, which are determined by the molecular size and polarizability. Since Br atoms are larger and more polarizable than Cl atoms, we can expect the London dispersion forces in \(\mathrm{CBr}_{4}\) to be stronger than those in \(\mathrm{CCl}_{4}\). Hence, \(\mathrm{CBr}_{4}\) would be less volatile than \(\mathrm{CCl}_{4}\). So the statement (a) is false.

(b) Compare the boiling points of \(\mathrm{CBr}_{4}\) and \(\mathrm{CCl}_{4}\)

Boiling point is directly related to the intermolecular forces between the molecules. Since we determined that \(\mathrm{CBr}_{4}\) has stronger London dispersion forces than \(\mathrm{CCl}_{4}\) due to the larger size and polarizability of Br atoms, we can infer that \(\mathrm{CBr}_{4}\) has a higher boiling point than \(\mathrm{CCl}_{4}\). So the statement (b) is true.

(c) Analyze the intermolecular forces of \(\mathrm{CBr}_{4}\) and \(\mathrm{CCl}_{4}\)

As discussed earlier, the intermolecular forces in both compounds are London dispersion forces, which rely on the molecular size and polarizability. Since Br atoms are larger and more polarizable than Cl atoms, we can infer that \(\mathrm{CBr}_{4}\) has stronger intermolecular forces than \(\mathrm{CCl}_{4}\). So the statement (c) is false.

(d) Compare the vapor pressures of \(\mathrm{CBr}_{4}\) and \(\mathrm{CCl}_{4}\) at the same temperature

Vapor pressure is the pressure exerted by a vapor in equilibrium with its condensed phase. It is inversely related to the intermolecular forces of the substance. As we have established that \(\mathrm{CBr}_{4}\) has stronger intermolecular forces than \(\mathrm{CCl}_{4}\), it will have a lower vapor pressure at the same temperature. So the statement (d) is false.