Question

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

Short answer

(a) vapor pressure has a high value with weak intermolecular forces.

Step-by-step solution

Understanding the Problem

We need to determine which property of a liquid will have a high value if the intermolecular forces (attractions between molecules) are weak. The given properties are vapor pressure, boiling point, viscosity, and surface tension.

Analyzing Vapor Pressure

Vapor pressure refers to the pressure exerted by a vapor in equilibrium with its liquid at a given temperature. Weak intermolecular forces mean molecules can escape more easily, leading to higher vapor pressure.

Considering Boiling Point

The boiling point is the temperature at which a liquid turns into vapor. If intermolecular forces are weak, it takes less energy to convert the liquid to vapor, resulting in a lower boiling point.

Examining Viscosity

Viscosity measures a liquid's resistance to flow. Stronger intermolecular forces result in higher viscosity. With weak attractions, the viscosity is generally low, not high.

Looking at Surface Tension

Surface tension arises from the cohesive forces among liquid molecules. Weak intermolecular forces result in low surface tension, not high.

Conclusion

Among the options, weak intermolecular forces are most associated with high vapor pressure, as molecules can transition to the vapor phase more easily compared to other properties discussed.

Key concepts

Vapor Pressure

Vapor pressure is a fascinating concept in chemistry. It refers to the pressure exerted by a gas or vapor in equilibrium with its liquid form at a given temperature. Imagine a container half filled with liquid; some molecules will escape into the vapor phase. This escaping tendency creates vapor pressure, a crucial factor in understanding evaporation and boiling processes.

Weak intermolecular forces make it easier for molecules to escape from a liquid's surface. When these forces are weak, the liquid readily vaporizes, resulting in a higher vapor pressure. Conversely, with strong intermolecular forces, molecules struggle to escape the liquid, leading to a lower vapor pressure.

• More vapor pressure means more molecules in the gas phase.
• High vapor pressure indicates easier evaporation.
• Weak attractions between molecules contribute to increased vapor formation.

Boiling Point

The boiling point of a liquid is the temperature at which its vapor pressure equals the external pressure surrounding the liquid. At this point, liquids turn into vapor, or boil. It is a direct reflection of how easily molecules can overcome intermolecular forces.

With weak molecular attractions, less energy is needed to convert a liquid into vapor. This results in a lower boiling point because the liquid transitions to vapor at a lower temperature. Strong intermolecular forces require more energy and thus, result in a higher boiling point.

• Boiling occurs when vapor pressure equals external pressure.
• Weak forces between molecules translate to lower boiling points.
• Stronger forces keep the liquid stable up to higher temperatures.

Viscosity

Viscosity is essentially how thick or sticky a liquid is; it describes a liquid's resistance to flow. Think of honey compared to water. Honey has higher viscosity because it flows slowly, thanks to stronger intermolecular forces among its molecules.

When intermolecular attractions are weak, the molecules slide past each other more easily, resulting in a lower viscosity. These weak forces mean the liquid flows more readily, making them less viscous compared to liquids with stronger molecular connections.

• High viscosity means slow flow, like in thick syrups.
• Weak molecular attractions result in low viscosity.
• Viscosity influences how liquids behave when poured or stirred.