Question

Ether has a higher vapor pressure than water. Which of these two liquids has stronger intermolecular forces? Which liquid would you expect to have the higher boiling point?

Short answer

Water has stronger intermolecular forces and a higher boiling point than ether.

Step-by-step solution

Identify Vapor Pressure and Intermolecular Forces

Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid or solid phase. Higher vapor pressure indicates weaker intermolecular forces, as molecules escape into the vapor phase more easily.

Compare Ether and Water

Given that ether has a higher vapor pressure than water, it means ether has weaker intermolecular forces compared to water.

Relate Intermolecular Forces to Boiling Point

Stronger intermolecular forces result in higher boiling points because more energy is needed to break these forces and convert the liquid into vapor. Since water has stronger intermolecular forces, it also has a higher boiling point than ether.

Conclusion

Water has stronger intermolecular forces and a higher boiling point compared to ether.

Key concepts

Vapor Pressure

Vapor pressure is the pressure exerted by the vapor of a liquid in equilibrium with its liquid phase. This means when the rate of evaporation equals the rate of condensation. Several factors affect vapor pressure, including temperature and the nature of the liquid itself.

Liquids with high vapor pressure, like ether, tend to have molecules that can escape easily into the vapor phase due to weaker intermolecular forces. On the contrary, substances with low vapor pressure, such as water, have strong intermolecular forces that keep the molecules bound together, making it harder for them to escape into the gas phase.

Thus, vapor pressure provides crucial insights into the strength of a liquid's intermolecular forces. If you know which liquid has a higher vapor pressure, you can infer which one has weaker intermolecular forces. This is essential in predicting how a liquid behaves under different conditions, such as boiling.

Boiling Point

The boiling point is the temperature at which a liquid's vapor pressure equals the surrounding atmospheric pressure. At this temperature, bubbles of vapor form within the liquid and rise to the surface to escape into the air.

Since breaking intermolecular forces requires energy, liquids with stronger intermolecular forces possess higher boiling points. For example, water has a higher boiling point than ether because water's molecules are held together by strong hydrogen bonds, while ether’s molecules are connected by weaker Van der Waals forces.

In practical terms, the concept of boiling point is vital in many industrial and laboratory processes. Understanding boiling points helps in the purification of liquids via distillation, cooking, and even in designing cooling systems that rely on phase transitions to regulate temperature.

Intermolecular Forces

Intermolecular forces are the forces that hold molecules together in a liquid or solid state. There are several types of intermolecular forces, including:

• Van der Waals forces: These are weak and arise from momentary dipoles formed when electrons orbit nuclei.
• Dipole-dipole interactions: These occur between molecules with permanent dipoles.
• Hydrogen bonds: These are strong dipole-dipole interactions that occur between a hydrogen atom bonded to electronegative atoms like oxygen, and another electronegative atom.

These forces determine many physical properties of liquids and solids, such as melting and boiling points, viscosity, and surface tension. For example, water, which has strong hydrogen bonds, exhibits higher boiling points and lower vapor pressures compared to ether, whose molecules are held together mainly by Van der Waals forces.

Understanding intermolecular forces not only helps in explaining why different substances behave the way they do but also allows the prediction of how the substance will react under various conditions. Knowledge of these interactions is crucial for fields like chemistry, materials science, and even pharmacology, where the physical state and behavior of substances can have significant implications.