General Chemistry Practice Exam - Intermolecular Forces, Liquids, Phase Changes, and Solutions

Flashcards covering intermolecular forces, phase diagrams, vapor pressure, liquid crystal behavior, heating curves, colligative properties, and solution chemistry from General Chemistry practice material.

What liquid crystal phase has all of the molecules lined up and arranged in distinct layers?

Smectic phase

What is meant by the term supercooling?

A liquid being present at a temperature below its freezing point, where it should normally be a solid

Why is the critical point for carbon dioxide substantially lower than the critical point for water?

The intermolecular forces are much weaker in carbon dioxide than in water

Which molecular characteristic does NOT favor liquid crystal behavior?

Being tightly coiled

What is the ease of deformation of a molecule's electron distribution called?

Polarizability

Why do liquids composed of long and flexible molecules have higher viscosity than liquids of spherical molecules?

Long and flexible molecules easily become tangled with one another

Why is the viscosity of glycerol ($\text{HOCH}_2\text{CHOHCH}_2\text{OH}$) much higher than that of n-propanol ($\text{CH}_3\text{CH}_2\text{CH}_2\text{OH}$)?

Glycerol has three hydroxyl groups capable of forming hydrogen bonds, compared to only one in n-propanol

What is meant by the statement that liquids exhibit short-range order?

Intermolecular forces are strong enough to keep molecules close together, but the molecules can still move relative to each other

Why is the thermal expansion of liquids relatively small?

Intermolecular forces are strong enough to hold the molecules close together

What is capillary action?

The tendency of polar liquids to rise inside small-diameter glass tubing

How much energy is required to convert $325\,\text{mL}$ of liquid water at $20\,^\circ\text{C}$ to steam at $100\,^\circ\text{C}$? ($\text{specific heat} = 4.184\,\text{J}/(\text{g}\cdot^\circ\text{C})$, $\Delta H_{\text{vap}} = 40.7\,\text{kJ/mol}$, $\text{density} = 0.998\,\text{g/mL}$)

$$441\,\text{kJ}$$

What is the definition of a London dispersion force?

An intermolecular attraction arising from temporary, induced dipoles between molecules

What is viscosity?

The resistance of a liquid to flow

How does dynamic equilibrium apply to vapor pressure?

Vaporization and condensation occur at equal rates, maintaining a constant pressure

Which of the following compounds has the highest boiling point: $\text{CH}_3\text{CH}_2\text{CH}_2\text{Cl}$, $\text{CH}_3\text{CH}_2\text{CH}_2\text{SH}$, $\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_3$, or $\text{CH}_3\text{CH}_2\text{CH}_2\text{OH}$?

$\text{CH}_3\text{CH}_2\text{CH}_2\text{OH}$ due to hydrogen bonding

What is the strongest intermolecular force present in acetone, $(\text{CH}_3)_2\text{C}=\text{O}$?

Dipole-dipole attractions

What is the strongest intermolecular force present in liquid bromine ($\text{Br}_2$)?

London dispersion forces

Why are different baking instructions required at high altitudes?

Atmospheric pressure is lower, which lowers the boiling point of water

What is sublimation?

The phase transition in which a solid converts directly into a gas without passing through the liquid phase

Arrange the alkanes $\text{C}_6\text{H}_{14}$, $\text{C}_4\text{H}_{10}$, $\text{C}_3\text{H}_8$, and $\text{C}_8\text{H}_{18}$ in order of increasing boiling point.

$$\text{C}_3\text{H}_8 < \text{C}_4\text{H}_{10} < \text{C}_6\text{H}_{14} < \text{C}_8\text{H}_{18}$$

Why is diffusion significantly slower in a liquid than in a gas?

Molecules in a liquid are packed closely together and collide frequently, traveling only short distances between collisions

How does a liquid exert a vapor pressure?

A fraction of molecules near the surface possess sufficient kinetic energy to overcome intermolecular forces and escape into the gas phase

What is a phase diagram?

A graphical representation showing the state of matter of a substance as a function of temperature and pressure

Why does water exhibit an exceptionally high surface tension?

Water molecules experience strong hydrogen bonding intermolecular forces

What is the triple point of a substance?

The specific temperature and pressure at which solid, liquid, and gas phases coexist in equilibrium

Why are dipole-dipole interactions weaker than ion-ion interactions?

Dipoles involve partial electric charges rather than full integer charges

What liquid crystal phase features aligned molecules that are free to slide past one another without forming organized layers?

Nematic phase

What is the definition of the normal boiling point of a liquid?

The temperature at which the vapor pressure of the liquid equals $1\,\text{atm}$ ($760\,\text{mmHg}$)

Why does $(\text{CH}_3)_3\text{CCl}$ boil at a lower temperature than $\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{Cl}$?

$(\text{CH}_3)_3\text{CCl}$ is more spherical with less surface area, resulting in weaker London dispersion forces

What are adhesive forces?

Attractive forces between molecules of a liquid and a surrounding solid surface

What is the critical temperature of a substance?

The temperature above which a gas cannot be liquefied, regardless of the amount of pressure applied

Why is the boiling point of water significantly higher than that of $\text{NH}_3$ or $\text{HF}$?

Water molecules form an extensive hydrogen-bonded network with an average of two hydrogen bonds per molecule

Why is the meniscus of mercury in glass convex while water is concave?

Cohesive forces among mercury atoms are stronger than adhesive forces to glass, whereas water adheres strongly to glass

What are the key properties of a supercritical fluid?

It displays gas-like property behavior (such as high diffusivity) while retaining liquid-like density and solvent ability

What structural characteristics define room-temperature ionic liquids?

They are composed of a small spherical anion combined with a large, bulky, asymmetric cation

Which structural feature enables a molecule to form hydrogen bonds?

A hydrogen atom directly bonded to nitrogen, oxygen, or fluorine

What is a volatile liquid?

A liquid that has a high vapor pressure and readily evaporates at room temperature

What is enthalpy of fusion ($\Delta H_{\text{fus}}$)?

The quantity of heat energy required to melt one mole of a solid substance at its melting point

How do stronger intermolecular forces affect vapor pressure?

Stronger intermolecular forces reduce the number of escaping molecules, lowering the vapor pressure

What is an amalgam?

A solution or mixture of one or more metals dissolved in liquid mercury

Why does a solute lower the freezing point of a solvent?

Solute particles disrupt the orderly formation of solvent crystal lattices

What is entropy ($S$)?

A thermodynamic measure of the disorder or randomness in a physical system

How can colloids be visually distinguished from true solutions?

Colloids scatter visible light (Tyndall effect), whereas true solutions are clear and do not scatter light

What is an ideal solution?

A solution that obeys Raoult's law across all concentration ranges because solute-solvent interactions equal solute-solute and solvent-solvent interactions

How do crown ethers enhance the solubility of ionic salts in nonpolar solvents?

The oxygen lone pairs of crown ethers complex and encapsulate cations, forming a nonpolar outer exterior

Why is the van 't Hoff factor of acetic acid dissolved in benzene measured to be less than 1?

Acetic acid molecules associate into dimers via hydrogen bonding in nonpolar solvents

What types of gases fail to obey Henry's law?

Gases that undergo chemical reactions with the solvent (such as $\text{NH}_3$ or $\text{HCl}$ in water)

What defines a colligative property?

A solution property that depends solely on the concentration (number) of solute particles, independent of their identity

What is reverse osmosis?

Applying pressure greater than the osmotic pressure to direct solvent flow from a concentrated solution to a dilute pure solvent side through a semipermeable membrane

What is molality ($m$)?

The ratio of moles of solute per kilogram of solvent ($\text{mol/kg}$)