Complete the following statements about the effect of intermolecular forces on the physical properties of a substance: (a) The higher the boiling point of a liquid, the (stronger, weaker) its intermolecular forces. (b) Substances with strong intermolecular forces have (high, low) vapor pressures. (c) Substances with strong intermolecular forces typically have (high, low) surface tensions. (d) The higher the vapor pressure of a liquid, the (stronger, weaker) its intermolecular forces. (c) Because nitrogen, \(\mathrm{N}_{2}\), has (strong, weak) intermolecular forces, it has a (high, low) critical temperature. (f) Substances with high vapor pressures have correspondingly (high, low) boiling points. (g) Because water has a relatively high boiling point, it must have (strong, weak) intermolecular forces and a correspondingly (high, low) enthalpy of vaporization.

Step by step solution

01

Relationship between Boiling Point and Intermolecular Forces

Understand that the boiling point of a substance indicates the temperature at which its liquid phase turns into gas. A higher boiling point signifies that more energy is required to overcome intermolecular forces. Therefore, the stronger the intermolecular forces, the higher the energy needed.

02

Effect of Intermolecular Forces on Vapor Pressure

Recognize that vapor pressure is the pressure of a vapor in equilibrium with its non-vapor phases at a given temperature. Strong intermolecular forces would mean that fewer molecules can escape the liquid to form vapor, resulting in a low vapor pressure.

03

Influence of Intermolecular Forces on Surface Tension

Note that surface tension is the elastic tendency of liquids which makes them acquire the least surface area possible. Substances with strong intermolecular forces have particles that are more attracted to each other, leading to a high surface tension.

04

Connection between Vapor Pressure and Intermolecular Forces

Understand that a high vapor pressure means that the substance's molecules can easily overcome the intermolecular forces to escape into the gas phase. This suggests that the intermolecular forces are weaker if the vapor pressure is higher.

05

Deduction of Nitrogen's Intermolecular Forces and Critical Temperature

Nitrogen, N2, is known to have weak intermolecular forces because it is a non-polar molecule with only London dispersion forces acting between its molecules. Weak intermolecular forces correspond to a low critical temperature for nitrogen.

06

Relation between Vapor Pressures and Boiling Points

Understand that a high vapor pressure indicates that a substance can more readily turn into vapor, which means it has a lower boiling point. This is because it takes less heat for the substance to reach the vapor pressure of the surrounding atmosphere.

07

Conclusion about Water's Intermolecular Forces and Enthalpy of Vaporization

Water has a high boiling point, which implies strong intermolecular forces (particularly hydrogen bonding). Strong intermolecular forces require more energy to overcome during the change from liquid to gas; therefore, water has a high enthalpy of vaporization.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Boiling Point

Considering the boiling point of a substance reveals a lot about its molecular interactions. The boiling point is the temperature at which a substance shifts from liquid to gas state. In essence, this point is where the atmospheric pressure equals the vapor pressure of the liquid.

Higher boiling points indicate that a liquid's molecules are clinging together more tightly due to stronger intermolecular forces. This means that more thermal energy, or heat, is required to separate these molecules and allow them to escape into the gas phase. For example, comparing water and acetone, water has a higher boiling point, indicating stronger intermolecular forces, specifically hydrogen bonds.

Vapor Pressure

Vapor pressure is a critical concept when examining the physical properties of substances. It is defined as the pressure exerted by a vapor in equilibrium with its liquid (or solid) at a given temperature. When we say a substance has a high vapor pressure at a particular temperature, it means that the molecules of the liquid have a higher tendency to escape into the vapor phase.

Substances with strong intermolecular forces tend to have lower vapor pressures because these forces make it difficult for the molecules to leave the liquid phase. Conversely, weak intermolecular forces correspond to higher vapor pressures.

Surface Tension

Surface tension is a fascinating phenomenon that occurs at the interface between liquid and air. It is caused by the cohesive forces between liquid molecules, which are stronger than the adhesive forces between the liquid and the surrounding environment.

This disparity in forces results in the liquid minimizing its surface area, creating a surface that resists external force. Substances with strong intermolecular forces exhibit high surface tension, leading to effects such as water droplets forming spherical shapes and insects like the water strider walking on water.

Critical Temperature

The critical temperature of a substance is the highest temperature at which it can exist as a liquid, regardless of pressure. Above this temperature, the substance can only exist as a gas. This is due to the kinetic energy of the molecules, which at high temperatures, overcomes even the strongest intermolecular forces.

For instance, substances with weak intermolecular forces, such as nitrogen, have a low critical temperature. This is because it takes less thermal energy to disrupt the forces between their molecules.

Enthalpy of Vaporization

The enthalpy of vaporization, also known as the heat of vaporization, refers to the amount of energy required to transform one mole of a liquid into gas at constant temperature and pressure. This energy breaks the intermolecular forces that hold the liquid molecules together.

Compounds with strong intermolecular forces, like water, have higher enthalpies of vaporization. Thus, a substantial amount of energy is needed for these substances to vaporize, underscoring the strength of their molecular bonds.

Hydrogen Bonding

Hydrogen bonding is one of the strongest types of intermolecular forces and occurs when a hydrogen atom covalently bonded to a highly electronegative atom, such as nitrogen, oxygen, or fluorine, experiences the electrostatic pull from another electronegative atom with a lone pair of electrons.

Substances that can form hydrogen bonds typically exhibit unique properties, such as high boiling points, high surface tension, and high enthalpy of vaporization. Water is a classic example; its remarkable properties are largely due to its ability to form extensive hydrogen bonding networks.

London Dispersion Forces

London dispersion forces, also known as Van der Waals forces, are the weakest type of intermolecular force. They are present in all molecules, whether polar or nonpolar, and arise due to the fluctuating electron clouds that can create temporary, instantaneous dipoles.

These forces are significant in nonpolar molecules like gases (e.g., \(\mathrm{N}_{2}\)) as they are the only kind of intermolecular interaction present. The strength of London dispersion forces increases with the size of the molecules and the number of electrons available to create fleeting dipoles.