General Chemistry: Intermolecular Forces, Liquids, Solids, and Phase Changes

Comprehensive practice flashcards covering intermolecular forces, physical properties of liquids, phase diagrams, heating curves, and classifications of solids from Chemistry Chapters 12 and 13.

How do the three phases of matter (solid, liquid, gas) differ in compressibility, density, and ability to flow?

Solids are rigid, dense, essentially incompressible, and do not flow. Liquids are dense, slightly compressible, and flow. Gases are least dense, highly compressible, flow, and expand to fill their container.

What is the difference between intramolecular forces and intermolecular forces (IMFs)?

Intramolecular forces exist within a compound (e.g., ionic bonds between metals and nonmetals, covalent bonds between nonmetals). Intermolecular forces exist between different molecules (e.g., dipole-dipole forces, hydrogen bonding, and London dispersion forces).

Which four elements are highlighted as having particularly high electronegativity?

Nitrogen ($\text{N}$), oxygen ($\text{O}$), fluorine ($\text{F}$), and chlorine ($\text{Cl}$).

Which molecular geometries are always polar?

Bent, trigonal pyramidal, seesaw, T-shaped, and square pyramidal.

Which molecular geometries can be nonpolar if outer terminal atoms are identical?

Linear, trigonal planar, tetrahedral, trigonal bipyramidal, octahedral, and square planar.

Based on electronegativity differences ($\Delta\text{EN}$), why is a $\text{C}-\text{H}$ bond considered nonpolar while a $\text{C}-\text{F}$ bond is polar?

For $\text{C}-\text{H}$, $\Delta\text{EN} = 2.5 - 2.1 = 0.4$ (which is $< 0.5$, making it nonpolar). For $\text{C}-\text{F}$, $\Delta\text{EN} = 4.0 - 2.5 = 1.5$, creating a significant dipole and making it polar.

What are dipole-dipole forces and what is their approximate strength relative to covalent or ionic bonds?

Dipole-dipole forces are electrostatic attractions between polar molecules with permanent dipole moments. They are approximately $1\%$ as strong as covalent or ionic bonds.

Why does formaldehyde ($\text{CH}_2\text{O}$) have a higher boiling point ($-19.5^\circ\text{C}$) than ethane ($\text{C}_2\text{H}_6$, bp $-88^\circ\text{C}$) despite their similar molar masses?

Formaldehyde is a polar molecule exhibiting dipole-dipole forces, whereas ethane is nonpolar and only exhibits weaker London dispersion forces. Stronger intermolecular forces lead to a lower vapor pressure and higher boiling point.

What two conditions are required for hydrogen bonding to occur?

A hydrogen atom covalently bonded directly to a highly electronegative atom ($\text{N}$, $\text{O}$, or $\text{F}$) acting as the donor, and another electronegative atom ($\text{N}$, $\text{O}$, or $\text{F}$) acting as the acceptor.

How do the boiling points and viscosities of the structural isomers dimethyl ether ($(\text{CH}_3)_2\text{O}$) and ethanol ($\text{CH}_3\text{CH}_2\text{OH}$) compare?

Dimethyl ether has a boiling point of $-24^\circ\text{C}$ and viscosity of $0.184\,\text{mm}^2/\text{s}$, while ethanol has a boiling point of $78^\circ\text{C}$ and viscosity of $1.31\,\text{mm}^2/\text{s}$ because ethanol can participate in hydrogen bonding.

What are London dispersion forces (LDF) and what factors determine their strength?

LDFs are temporary/accidental dipoles that induce dipoles in neighboring particles. Their strength depends on polarizability, which increases with more electrons (higher molar mass) and less molecular branching (straight chains provide more surface contact).

What is the primary intermolecular force in pure samples of $\text{BF}_3$, $\text{CH}_3\text{NH}_2$, and $\text{PCl}_3$?

$\text{BF}_3$ is nonpolar and exhibits London dispersion forces (LDF); $\text{CH}_3\text{NH}_2$ is polar with an $\text{N}-\text{H}$ bond and exhibits hydrogen bonding; $\text{PCl}_3$ is polar (trigonal pyramidal) and exhibits dipole-dipole forces.

What is the strongest intermolecular force operating in a mixture of an ionic compound and a nonpolar compound?

Ion-induced dipole force.

What is the typical energy range of ion-dipole forces compared to hydrogen bonding?

Ion-dipole forces typically range from $40\text{ to }600\,\text{kJ/mol}$, whereas hydrogen bonds range from $10\text{ to }40\,\text{kJ/mol}$.

What is dynamic liquid-vapor equilibrium in a closed system?

A state where the rate of vaporization equals the rate of condensation, resulting in a constant vapor pressure at a constant temperature.

How do temperature and intermolecular force strength affect vapor pressure?

Higher temperature increases vapor pressure (molecules move faster and more readily overcome IMFs). Weaker intermolecular forces lead to higher vapor pressure.

What is the linear form of the Clausius-Clapeyron equation, and what do its slope and intercept represent on a plot of $\ln(P)$ versus $1/T$?

$\ln(P) = -\frac{\Delta H_{\text{vap}}}{R}\left(\frac{1}{T}\right) + B$. The slope ($m$) is $-\frac{\Delta H_{\text{vap}}}{R}$ and the y-intercept ($b$) is $B = \ln(A)$.

What is the two-point form of the Clausius-Clapeyron equation?

$\ln\left(\frac{P_2}{P_1}\right) = -\frac{\Delta H_{\text{vap}}}{R}\left(\frac{1}{T_2} - \frac{1}{T_1}\right)$, where $R = 8.314\,\text{J}/(\text{mol}\cdot\text{K})$.

What defines the normal boiling point of a liquid?

The temperature at which the vapor pressure of the liquid equals atmospheric pressure at sea level ($1\,\text{atm}$ or $760\,\text{torr}$).

How are viscosity and surface tension defined, and how do they trend with IMF strength?

Viscosity is the resistance of a liquid to flow (measured in $\text{g}/(\text{cm}\cdot\text{s})$ or poise); surface tension is the energy required to increase the surface area ($\text{J}/\text{m}^2$). Both increase as intermolecular forces become stronger.

What causes capillary action and the meniscus curvature of a liquid?

Capillary action results from adhesive forces pulling liquid up a tube wall while cohesive forces pull interior liquid with it. The meniscus curve is caused by competition between adhesive and cohesive forces.

Why does $\text{BI}_3$ (bp $209.5^\circ\text{C}$) have a higher boiling point than $\text{NH}_3$ (bp $-33.0^\circ\text{C}$), even though $\text{NH}_3$ forms hydrogen bonds?

London dispersion forces can dominate over hydrogen bonding when there are large differences in molar mass ($\text{BI}_3$ has a molar mass of $391.5\,\text{g/mol}$ versus $17.0\,\text{g/mol}$ for $\text{NH}_3$).

What are the structural units, forces, and properties of ionic solids versus molecular solids?

Ionic solids consist of cations and anions held by ionic bonds; they have high melting points, are hard and brittle, nonconducting as solids, and conductive when melted or dissolved. Molecular solids consist of molecules held by IMFs (LDF, dipole-dipole, H-bonds); they have low to moderate melting points and are electrical nonconductors.

What are the structural units, forces, and properties of metallic solids versus covalent network solids?

Metallic solids consist of metal atoms held by delocalized metallic bonds ("sea of electrons"); they have variable melting points/hardness, are malleable, and conduct heat/electricity well. Covalent network solids consist of atoms joined by covalent bonds; they have very high melting points, extreme hardness, are brittle, and are non- or semiconductors.

What are allotropes, and what carbon and sulfur allotropes are described in the notes?

Allotropes are different solid structural forms of the same element. Carbon allotropes include graphite ($\Delta H^\circ_f = 0$), diamond ($\Delta H^\circ_f \neq 0$), and graphene. Sulfur allotropes include rhombic and monoclinic forms.

What are the triple point and the critical point on a phase diagram?

The triple point is the unique temperature and pressure at which all three phases (solid, liquid, gas) coexist in equilibrium. The critical point is the temperature and pressure beyond which a supercritical fluid exists with no distinct liquid or gas phases.

How does the slope of the solid-liquid line on a phase diagram reflect relative densities?

A positive slope indicates that the solid is denser than the liquid ($d_s > d_l$). A negative slope (as seen in water) indicates that the liquid is denser than the solid ($d_s < d_l$).

What are the formulas used for calculating heat during a temperature change versus a phase change?

For a temperature change, $q = s \cdot m \cdot \Delta T$ (where $s$ is specific heat capacity). For a phase change at constant temperature, $q = \Delta H \cdot m$ (or $q = \Delta H \cdot n$).

What are the five steps needed to heat ice at $-25.0^\circ\text{C}$ to steam at $125.0^\circ\text{C}$?

1. Warm ice from $-25.0^\circ\text{C}$ to $0.0^\circ\text{C}$ ($q = s_{\text{ice}} m \Delta T$); 2. Melt ice at $0.0^\circ\text{C}$ ($q = \Delta H_{\text{fus}} m$); 3. Warm water from $0.0^\circ\text{C}$ to $100.0^\circ\text{C}$ ($q = s_{\text{water}} m \Delta T$); 4. Vaporize water at $100.0^\circ\text{C}$ ($q = \Delta H_{\text{vap}} m$); 5. Warm steam from $100.0^\circ\text{C}$ to $125.0^\circ\text{C}$ ($q = s_{\text{steam}} m \Delta T$).

What are the three categories of ceramics and their typical applications?

Silicate ceramics (e.g., clays/aluminosilicates used in porcelain); oxide ceramics (e.g., $\text{Al}_2\text{O}_3$, $\text{MgO}$ used in crucibles); and non-oxide ceramics (e.g., $\text{Si}_3\text{N}_4$, $\text{BN}$, $\text{SiC}$ used in engine parts and lubricants).

What is Portland cement made of, and how is concrete produced from it?

Portland cement is composed of limestone, silica, alumina, iron oxide, and gypsum. It reacts with water to form a solid binding agent and is combined with sand and pebbles to make concrete.

How do soda-lime glass, borosilicate glass (Pyrex), and leaded glass differ?

Soda-lime glass is $70\%$ $\text{SiO}_2$ and $30\%$ $\text{Na}_2\text{O}$ & $\text{CaO}$; borosilicate glass replaces $\text{CaO}$ with $\text{B}_2\text{O}_3$ to reduce thermal expansion; leaded glass replaces $\text{CaO}$ with $\text{PbO}$ to provide a higher index of refraction.