Gen Chem 2-- CH 12

Flashcards covering the vocabulary from the lecture notes about intermolecular forces, liquids, and solids.

Intermolecular Forces

Forces of attraction between molecules.

Intramolecular Forces

Forces that hold atoms together within a molecule.

Thermal Energy

Energy associated with the random motion of molecules and atoms in matter.

Dispersion Forces

A type of intermolecular force present in all molecules, resulting from temporary fluctuations in electron distribution.

Dipole

A measurement of the separation of positive and negative charges.

Dipole-Dipole Forces

Intermolecular forces that occur between polar molecules due to the attraction of positive and negative ends.

Miscibility

The ability of two or more liquids to dissolve and mix together.

Hydrogen Bonding

A strong type of dipole-dipole attraction between a hydrogen atom bonded to a highly electronegative atom (such as N, O, or F) and another electronegative atom in a different molecule.

Ion-Dipole Force

An intermolecular force between an ion and a polar molecule.

Surface Tension

The tendency of liquids to minimize surface area, resulting from the inward attraction of surface molecules.

Viscosity

A measure of a liquid's resistance to flow.

Capillary Action

The ability of a liquid to flow in narrow spaces due to adhesive and cohesive forces.

Vaporization

The process by which a liquid changes into a gas.

Condensation

The process by which a gas changes into a liquid.

Dynamic Equilibrium

The state where the rate of vaporization equals the rate of condensation in a closed system, resulting in a constant vapor pressure.

Vapor Pressure

The pressure exerted by a vapor in equilibrium with its liquid or solid phase.

Normal Boiling Point

The temperature at which the vapor pressure of a liquid equals the external pressure of 1 atm.

Sublimation

The process by which a solid changes directly into a gas.

Deposition

The process by which a gas changes directly into a solid.

Fusion

The process by which a solid changes into a liquid (melting).

Freezing

The process by which a liquid changes into a solid.

Triple Point

The temperature and pressure at which the solid, liquid, and vapor phases of a substance coexist in equilibrium.

Critical Point

The temperature and pressure above which a distinct liquid phase does not exist.

Supercritical Fluid

A substance above its critical temperature and pressure, exhibiting properties of both a liquid and a gas.

How does thermal energy affect intermolecular forces?

Thermal energy increases molecular motion, which can disrupt intermolecular forces. Higher temperatures weaken these forces, leading to phase changes such as melting or vaporization.

Explain the relationship between intermolecular forces and boiling point.

Substances with stronger intermolecular forces have higher boiling points because more energy is required to overcome these forces and transition the substance from a liquid to a gaseous state.

What determines the strength of dispersion forces?

The strength of dispersion forces depends on the size and shape of the molecule. Larger molecules with more electrons and greater surface area have stronger dispersion forces due to increased temporary fluctuations in electron distribution.

How does hydrogen bonding affect the properties of water?

Hydrogen bonding in water leads to high surface tension, high boiling point, and unique properties such as ice being less dense than liquid water, which is essential for aquatic life.

Describe the energy changes associated with phase transitions.

Phase transitions involve changes in energy. For example, vaporization requires energy input (heat of vaporization) to overcome intermolecular forces, while condensation releases energy (heat of condensation) as molecules come closer together.

How does viscosity relate to intermolecular forces?

Viscosity increases with stronger intermolecular forces because these forces resist the movement of molecules past each other. Substances with high intermolecular forces, such as hydrogen bonding, tend to have higher viscosities.

Explain the significance of the triple point on a phase diagram.

The triple point on a phase diagram indicates the specific temperature and pressure at which all three phases (solid, liquid, and gas) of a substance coexist in equilibrium. It provides a unique set of conditions for phase studies.

What happens to a substance at its critical point?

At the critical point, the liquid and gas phases of a substance become indistinguishable. Above this point, the substance exists as a supercritical fluid, which has properties of both a liquid and a gas.

Compare and contrast intermolecular and intramolecular forces.

Intermolecular forces are attractions between molecules and influence physical properties like boiling point and viscosity. Intramolecular forces are forces within a molecule that hold atoms together and determine chemical properties.

Describe the process of dynamic equilibrium between liquid and vapor phases.

In a closed system, dynamic equilibrium occurs when the rate of vaporization equals the rate of condensation. This results in a constant vapor pressure as molecules continuously move between the liquid and gas phases.

Explain how thermal expansion and contraction relate to intermolecular forces.

When thermal energy is added, molecules move faster and overcome intermolecular forces to spread out, leading to expansion. Conversely, when thermal energy is removed, molecules slow down, and intermolecular forces draw them closer together, leading to contraction.

How do dipole-dipole forces arise, and what factors influence their strength?

Polar molecules align themselves so that the positive end of one molecule is near the negative end of another, creating an attractive force. The strength of this force depends on the magnitude of the dipoles; larger dipoles result in stronger dipole-dipole forces.

Under what conditions does hydrogen bonding occur, and why is it so strong?

Hydrogen bonding occurs when hydrogen is bonded to a highly electronegative atom (N, O, or F). The small size of hydrogen and high electronegativity difference result in a strong partial positive charge on the hydrogen, which is then strongly attracted to the lone pair of electrons on the electronegative atom of another molecule.

What causes surface tension in liquids?

Surface tension arises from cohesive forces between liquid molecules. Molecules at the surface experience a net inward force, which causes the liquid to minimize its surface area and behave as if it has a 'skin.'

How does temperature affect vapor pressure, and how does this relate to boiling point?

As temperature increases, more molecules have enough kinetic energy to overcome intermolecular forces and escape into the gas phase, increasing the vapor pressure. The substance boils when its vapor pressure equals the external pressure, and thus the boiling point increases.

What information can be obtained from a phase diagram?

A phase diagram illustrates the conditions (temperature and pressure) under which different phases of a substance are thermodynamically stable. It shows the boundaries between phases and key points such as the triple point and critical point.

What factors affect the viscosity of a liquid?

The stronger the intermolecular forces in a liquid, the more it resists flowing, leading to higher viscosity. Additionally, molecular shape and size affect viscosity, as larger and more irregularly shaped molecules tend to have higher viscosity due to increased interactions.

Explain the roles of adhesive and cohesive forces in capillary action.

Capillary action is due to the interplay of adhesive forces (attraction between liquid and container) and cohesive forces (attraction between liquid molecules). If adhesive forces are stronger, the liquid will rise in the tube (e.g., water in glass). If cohesive forces are stronger, the liquid level will be lower inside the tube (e.g., mercury in glass).

Describe the process of sublimation and the conditions under which it occurs.

During sublimation, a solid absorbs energy to overcome intermolecular forces and directly transforms into a gas, without passing through the liquid phase. This occurs when the solid's vapor pressure reaches the surrounding pressure at a temperature below the melting point.