Question

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.

Short answer

Butane has the highest vapor pressure; Toluene has the lowest.

Step-by-step solution

Understand Vapor Pressure and Boiling Point

Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid at a given temperature. A liquid boils when its vapor pressure equals the atmospheric pressure. Therefore, a lower boiling point indicates a higher vapor pressure at any given temperature below the boiling point.

List the Boiling Points

The boiling points of the listed compounds are: Butane: \(-0.5^{\circ} \mathrm{C}\), Ethanol: \(78.3^{\circ} \mathrm{C}\), and Toluene: \(110.6^{\circ} \mathrm{C}\).

Determine Highest Vapor Pressure

Compare the boiling points: Butane has the lowest boiling point (\(-0.5^{\circ} \mathrm{C}\)) among the three. Since it has the lowest boiling point, butane will have the highest vapor pressure at \(-10^{\circ} \mathrm{C}\).

Determine Lowest Vapor Pressure

Since Toluene has the highest boiling point (\(110.6^{\circ} \mathrm{C}\)), it will have the lowest vapor pressure at \(-10^{\circ} \mathrm{C}\).

Key concepts

Understanding Boiling Point

The boiling point of a substance is the temperature at which it changes from a liquid to a gas. At this point, the vapor pressure of the liquid equals the atmospheric pressure surrounding it.
This temperature can vary depending on the atmospheric pressure, so substances have different boiling points at different altitudes.
A lower boiling point means that a liquid can turn to gas at a lower temperature.

• Liquids with low boiling points, like butane, boil more easily because their vapor pressure reaches the atmospheric pressure faster.
• In contrast, liquids with high boiling points, such as toluene, require more energy (or heat) to reach the boiling point.

Understanding boiling points helps us predict behaviors of liquids at different conditions. The concept of boiling points is vital in both practical applications like cooking and technological processes in various industries.

The Concept of Equilibrium in Vapor Pressure

Equilibrium occurs when a system is in balance, with no net change occurring over time. When a liquid is in equilibrium with its vapor, the rate at which molecules leave the liquid to become vapor (evaporation) equals the rate at which vapor molecules return to the liquid (condensation).

In terms of vapor pressure, equilibrium is reached when the pressure exerted by the vapor above the liquid remains constant.

• This vapor pressure is dependent on the temperature and the nature of the liquid.
• Different liquids achieve equilibrium at different vapor pressures and temperatures. For instance, butane reaches equilibrium at a higher vapor pressure than toluene at any temperature below their respective boiling points.

Understanding this equilibrium helps in various fields such as chemistry and meteorology, where predicting behavior of liquids and gases is necessary.

Exploring Compounds and Their Properties

Compounds are substances made from two or more elements chemically bonded together. Each compound has its own unique set of properties, such as boiling point, melting point, and density.
These properties are key in determining how a compound behaves under different conditions.
For example, the boiling points of butane, ethanol, and toluene differ significantly due to their molecular structures and intermolecular forces.

• Butane has a simpler, smaller molecular structure, resulting in a lower boiling point.
• Ethanol, having hydrogen bonds, has a higher boiling point compared to butane.
• Toluene, with its aromatic ring, has the highest boiling point among the three.

Understanding these properties helps scientists and engineers in selecting appropriate compounds for specific uses, like solvents in chemical reaction processes and designing efficient storage and transportation systems for different substances.