Intermolecular Forces and Liquids and Solids

Comprehensive practice questions covering intermolecular forces, liquid properties, crystal types, phase changes, and relevant chemical equations based on the lecture notes.

What is the definition of a phase?

A homogeneous part of the system in contact with other parts of the system but separated from them by a well-defined boundary.

Distinguish between intermolecular and intramolecular forces.

Intermolecular forces are attractive forces between molecules, while intramolecular forces hold atoms together in a molecule.

How much energy is required to vaporize $1\,mol$ of water compared to breaking all $O-H$ bonds in the same amount of water?

It takes $41\,kJ$ to vaporize $1\,mol$ of water (intermolecular) and $930\,kJ$ to break all $O-H$ bonds (intramolecular).

What physical properties serve as a "measure" of intermolecular force?

Boiling point, melting point, $\Delta H_{vap}$, $\Delta H_{fus}$, and $\Delta H_{sub}$.

What are dipole-dipole forces?

Attractive forces between polar molecules.

Define ion-dipole forces.

Attractive forces between an ion and a polar molecule.

What are dispersion forces?

Attractive forces that arise as a result of temporary dipoles induced in atoms or molecules.

What is a hydrogen bond?

A special dipole-dipole interaction between the hydrogen atom in a polar $N-H$, $O-H$, or $F-H$ bond and an electronegative $O$, $N$, or $F$ atom.

Define polarizability.

The ease with which the electron distribution in the atom or molecule can be distorted.

What factors cause polarizability to increase?

A greater number of electrons and a more diffuse electron cloud.

How do melting and boiling points change as the number of electrons in a molecule increases?

Melting and boiling points increase because more electrons lead to a larger molar mass and stronger dispersion forces.

What is surface tension?

The amount of energy required to stretch or increase the surface of a liquid by a unit area.

Contrast cohesion and adhesion.

Cohesion is the intermolecular attraction between like molecules, while adhesion is an attraction between unlike molecules.

What is viscosity?

A measure of a fluid's resistance to flow.

At what temperature does water reach its maximum density?

$40C$ (Note: per transcript page 24).

Contrast crystalline and amorphous solids.

A crystalline solid possesses rigid and long-range order with atoms, molecules, or ions in predictable positions; an amorphous solid lacks a well-defined arrangement and long-range molecular order.

What is a glass?

An optically transparent fusion product of inorganic materials that has cooled to a rigid state without crystallizing.

What is the Bragg Equation used for X-ray diffraction?

$2d \sin(\theta) = n\lambda$.

What are the characteristics of ionic crystals?

Lattice points are occupied by cations and anions held by electrostatic attraction; they are hard, brittle, have high melting points, and are poor conductors of heat and electricity.

What are covalent crystals, and what are two examples provided?

Crystals where lattice points are occupied by atoms held together by covalent bonds; examples include diamond and graphite.

What are the characteristics of molecular crystals?

Lattice points are occupied by molecules held by intermolecular forces; they are soft, have low melting points, and are poor conductors of heat and electricity.

How are metallic crystals held together and what is their conductivity?

They are held together by metallic bonds (a mobile "sea" of electrons) and are good conductors of heat and electricity.

What is equilibrium vapor pressure?

The vapor pressure measured when a dynamic equilibrium exists between condensation and evaporation (Rate of condensation = Rate of evaporation).

Define molar heat of vaporization ($\Delta H_{vap}$).

The energy required to vaporize $1\,mol$ of a liquid at its boiling point.

What is the Clausius-Clapeyron Equation?

$\ln(P) = - \frac{\Delta H_{vap}}{RT} + C$, where $R = 8.314\,J/K \cdot mol$.

Define boiling point and normal boiling point.

The boiling point is the temperature where equilibrium vapor pressure equals external pressure; the normal boiling point is the temperature at which a liquid boils when external pressure is $1\,atm$.

Define critical temperature ($T_c$) and critical pressure ($P_c$).

$T_c$ is the temperature above which a gas cannot be liquefied regardless of pressure; $P_c$ is the minimum pressure required to liquefy a gas at its critical temperature.

What is the molar heat of fusion ($\Delta H_{fus}$)?

The energy required to melt $1\,mol$ of a solid substance at its freezing point.

Define molar heat of sublimation ($\Delta H_{sub}$) and its relationship to other heats of transition.

It is the energy required to sublime $1\,mol$ of a solid; according to Hess's Law, $\Delta H_{sub} = \Delta H_{fus} + \Delta H_{vap}$.

What is a phase diagram?

A summary of the conditions at which a substance exists as a solid, liquid, or gas.