True or false: (a) CBr4 is more volatile than CCl4. (b) CBr4 has a higher vapor pressure at the same temperature than CCl4.

Verified step by step guidance

Step 1: Understand the concept of volatility and vapor pressure. Volatility refers to how easily a substance vaporizes, while vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid or solid phase at a given temperature.

Step 2: Consider the molecular structure and intermolecular forces. Both CBr4 and CCl4 are tetrahedral molecules, but they differ in the halogen atoms attached to the carbon atom.

Step 3: Analyze the intermolecular forces. CBr4 and CCl4 are nonpolar molecules, so they primarily exhibit London dispersion forces. The strength of these forces increases with the size and mass of the molecule.

Step 4: Compare the molecular weights. CBr4 has a higher molecular weight than CCl4 because bromine atoms are heavier than chlorine atoms. This generally leads to stronger London dispersion forces in CBr4.

Step 5: Relate intermolecular forces to volatility and vapor pressure. Stronger intermolecular forces in CBr4 mean it is less volatile and has a lower vapor pressure compared to CCl4 at the same temperature.

Key Concepts

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

Volatility

Volatility refers to the tendency of a substance to vaporize. It is influenced by intermolecular forces; substances with weaker forces tend to be more volatile. In this context, comparing CBr4 and CCl4 involves understanding how their molecular structures and the strength of their intermolecular forces affect their ability to transition into the gas phase.

Vapor Pressure

Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid or solid form at a given temperature. It is a measure of a substance's volatility; higher vapor pressure indicates a greater tendency to evaporate. The comparison between CBr4 and CCl4 requires knowledge of how molecular weight and intermolecular forces impact their respective vapor pressures.

Intermolecular Forces

Intermolecular forces are the forces of attraction or repulsion between neighboring particles (atoms, molecules, or ions). These forces, including London dispersion forces, dipole-dipole interactions, and hydrogen bonding, significantly influence physical properties like boiling point and vapor pressure. Understanding the differences in intermolecular forces between CBr4 and CCl4 is crucial for evaluating their volatility and vapor pressures.

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Textbook Question

The critical temperatures and pressures of a series of halogenated methanes are as follows: (c) Predict the critical temperature and pressure for CCl4 based on the trends in this table. Look up the experimentally determined critical temperatures and pressures for CCl4, using a source such as the CRC Handbook of Chemistry and Physics, and suggest a reason for any discrepancies.

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Open Question

Which of the following affects the vapor pressure of a liquid? (a) Volume of the liquid, (b) surface area, (c) intermolecular attractive forces, (d) temperature, (e) density of the liquid

Textbook Question

(a) Place the following substances in order of increasing volatility: CH₄, CBr₄, CH₂Cl₂, CH₃Cl, CHBr₃, and CH₂Br₂. (b) How do the boiling points vary through this series? (c) Explain your answer to part (b) in terms of intermolecular forces.

(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?

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Textbook Question

You are high up in the mountains and boil water to make some tea. However, when you drink your tea, it is not as hot as it should be. You try again and again, but the water is just not hot enough to make a hot cup of tea. Which is the best explanation for this result? (a) High in the mountains, it is probably very dry, and so the water is rapidly evaporating from your cup and cooling it. (b) High in the mountains, it is probably very windy, and so the water is rapidly evaporating from your cup and cooling it. (c) High in the mountains, the air pressure is significantly less than 1 atm, so the boiling point of water is much lower than at sea level. (d) High in the mountains, the air pressure is significantly less than 1 atm, so the boiling point of water is much higher than at sea level.

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Textbook Question

Using the vapor-pressure curves in Figure 11.25, (d) estimate the external pressure at which diethyl ether will boil at 40 °C.

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