Question

If the molecules in a liquid are strongly attracted, which of the following properties has a high value? (a) vapor pressure (b) boiling point (c) viscosity (d) surface tension

Short answer

Boiling point, viscosity, and surface tension are high when molecules are strongly attracted.

Step-by-step solution

Understanding Molecular Attraction

When molecules in a liquid are strongly attracted to each other, they tend to stick together more. This affects various properties of the liquid, making it necessary to understand what each listed property represents.

Analyzing Vapor Pressure

Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid at a given temperature. Strong intermolecular attractions generally result in a low vapor pressure because molecules do not easily escape into the vapor phase.

Analyzing Boiling Point

Boiling point is the temperature at which a liquid's vapor pressure equals the external pressure. If the intermolecular attractions are strong, more energy (in the form of heat) is required to overcome these attractions, leading to a high boiling point.

Analyzing Viscosity

Viscosity is the measure of a fluid's resistance to flow. Strong attractions between molecules increase this resistance, resulting in a higher viscosity.

Analyzing Surface Tension

Surface tension refers to the energy required to increase the surface area of a liquid. Strong intermolecular attractions result in a high surface tension because the molecules prefer to stay together, minimizing surface area.

Identifying the Correct Property

Based on our analysis, strong molecular attraction in a liquid tends to increase properties such as boiling point, viscosity, and surface tension.

Key concepts

Boiling Point

The boiling point of a liquid is a significant concept to understand when discussing intermolecular forces. It is the temperature at which the vapor pressure of the liquid equals the atmospheric pressure surrounding it, allowing the liquid to transition into the vapor phase. Intermolecular forces play a crucial role here.

A liquid with strong intermolecular forces, like hydrogen bonds or dipole-dipole interactions, requires more energy input—usually in the form of heat—to break these attractions and allow the molecules to escape as vapor. This means that liquids with strong intermolecular attractions will have a high boiling point.

• Why High Boiling Point?: Strong attractions necessitate higher temperatures to break molecules apart.
• Impact of Surrounding Pressure: Changes in atmospheric pressure can alter the boiling point.

Understanding the boiling point helps in predicting how a substance behaves under thermal conditions and has practical applications like cooking or industrial processes.

Vapor Pressure

Vapor pressure is another important property influenced by the nature of molecular attraction in liquids. It refers to the pressure exerted by the vapor when it is in equilibrium with its liquid form at a given temperature. Strong intermolecular forces tend to hold the molecules together tightly, making it less likely for them to escape into the vapor phase.

As a result, substances with high intermolecular forces typically exhibit a low vapor pressure. This is because fewer molecules have the energy to escape into the gas phase.

• Low Vapor Pressure: Indicates strong intermolecular attractions, making transition to gas phase difficult.
• Equilibrium Considerations: At equilibrium, fewer molecules are present in vapor due to strong attractions.

Vapor pressure is an essential factor when studying evaporation, distillation, and even weather patterns.

Viscosity

Viscosity measures a liquid's resistance to flow and is heavily affected by intermolecular forces. If the molecules within a liquid are strongly attracted to each other, they will resist movement, which increases the liquid's viscosity. In essence, the stronger the intermolecular attractions, the thicker or more "syrupy" the liquid behaves.

This property is very important in industries where the flow characteristics of liquids are critical, such as oil refining or food production.

• High Viscosity: Indicates strong molecular interactions that prevent easy movement.
• Temperature Influence: Viscosity generally decreases with an increase in temperature, as heat overcomes some molecular attractions.

Understanding viscosity provides insight into a liquid's flow behavior and helps in determining appropriate applications or uses for various liquids.

Surface Tension

Surface tension refers to the energy required to increase the surface area of a liquid, arising due to intermolecular forces. Liquids with strong intermolecular attractions tend to have high surface tension. This is because the molecules prefer to be surrounded by similar molecules rather than being exposed to the air; hence, they pull together to minimize surface area.

This phenomenon is observable in nature, such as when water forms droplets or certain insects walk on water.

• High Surface Tension: Strong attractions mean high energy is needed for surface expansion.
• Practical Observations: The "skin-like" surface effect is due to minimized surface area.

Surface tension is crucial in various technological and biological applications, including detergent effectiveness and biological cell processes.