Intermolecular Forces and Physical Properties (5B) - Chem & Physics

What is the correct relation between boiling point and vapor pressure at $1\ \text{atm}$ ?

Normal boiling point is when vapor pressure equals $1\ \text{atm}$ . Boiling occurs when vapor pressure equals atmospheric pressure, standardized at $1\ \text{atm}$ for normal conditions.
What is the relationship between intermolecular force strength and surface tension?

Stronger intermolecular forces increase surface tension. Stronger cohesive forces pull surface molecules inward, minimizing surface area and increasing tension.
What is the defining feature of ion-dipole forces in solutions?

Attraction between an ion and the partial charges of a polar molecule. Full ionic charges attract the oppositely charged portions of polar solvent molecules like water.
Which atoms can serve as the hydrogen-bond donor atom directly bonded to H?

N, O, or F. These highly electronegative atoms polarize the H-X bond sufficiently for strong hydrogen bond formation.
Which option is more soluble in water: a polar solute or a nonpolar solute?

A polar solute ("like dissolves like") is more soluble in water. Polar solutes form favorable dipole or hydrogen bond interactions with water, enhancing solubility per "like dissolves like".
What is the relationship between intermolecular force strength and vapor pressure at a given $T$ ?

Stronger intermolecular forces decrease vapor pressure. Stronger forces retain more molecules in the liquid, reducing evaporation rate at a fixed temperature.
What is the formula for mole fraction of component $A$ , $\chi_A$ ?

$\chi_A=\frac{n_A}{\sum n_i}$ . Mole fraction represents the proportional contribution of a component to the total moles in a mixture.
Identify the correct boiling point elevation formula for a solution.

$\Delta T_b=iK_b m$ . Elevation is a colligative effect proportional to particle molality and the solvent's boiling constant $K_b$ .
Identify the correct osmotic pressure formula for a dilute solution.

$\Pi=iMRT$ . Osmotic pressure follows a relation analogous to the ideal gas law, based on effective molarity and temperature.
What is the correct phase-change relation between $\Delta H_{sub}$ , $\Delta H_{fus}$ , and $\Delta H_{vap}$ ?

$\Delta H_{sub}=\Delta H_{fus}+\Delta H_{vap}$ . Sublimation combines the processes of fusion and vaporization in a single solid-to-gas transition.
Which species most commonly serves as a hydrogen-bond acceptor in neutral molecules?

An electronegative atom with lone pairs, usually N or O (sometimes F). Lone pairs on electronegative atoms provide sites for electrostatic attraction to partially positive hydrogens.
What is the relationship between intermolecular force strength and enthalpy of vaporization, $ $\Delta H_{vap}$ ?

Stronger intermolecular forces increase $\Delta H_{vap}$ . More energy is needed to overcome stronger attractions when transitioning from liquid to gas.
What is the relationship between intermolecular force strength and boiling point?

Stronger intermolecular forces increase boiling point. Greater attractions require more thermal energy to separate molecules into the gas phase.
What is the relationship between intermolecular force strength and viscosity?

Stronger intermolecular forces increase viscosity. Increased attractions hinder molecular flow, making the liquid more resistant to deformation.
What is the defining feature of London dispersion forces between atoms or molecules?

Attractive forces from instantaneous and induced dipoles. Fluctuating electron distributions create temporary dipoles that induce similar dipoles in nearby molecules, leading to weak attractions.
Identify the correct freezing point depression formula for a nonelectrolyte solution.

$\Delta T_f=iK_f m$ . Colligative depression depends on effective particle concentration ( $i m$ ) and the solvent-specific constant $K_f$ .
What is the formula for molarity, $M$ ?

$M=\frac{\text{mol solute}}{\text{L solution}}$ . Molarity quantifies solute concentration based on total solution volume, useful for volumetric calculations.
What molecular property most directly increases London dispersion forces in a series?

Greater polarizability (larger electron cloud; higher molar mass). Larger, more distortable electron clouds enhance temporary dipole formation and strength of induced attractions.
Which structural change increases London dispersion forces: more branching or less branching?

Less branching (greater surface area) increases dispersion forces. Straighter chains provide more surface area for contact, strengthening induced dipole interactions.
What specific requirement must be met for hydrogen bonding to occur between molecules?

H bonded to N, O, or F; interacts with N, O, or F lone pair. High electronegativity creates a strongly partial positive H, enabling attraction to lone pairs on another electronegative atom.
What is the formula for molality, $m$ ?

$m=\frac{\text{mol solute}}{\text{kg solvent}}$ . Molality uses solvent mass, providing a temperature-independent concentration measure for colligative properties.
What is the correct ranking of intermolecular forces from weakest to strongest?

London dispersion < dipole-dipole < hydrogen bonding < ion-dipole < ionic. This ranking reflects increasing interaction strength from temporary induced dipoles to permanent charge attractions and full ionic bonds.
What is Raoult's law for the vapor pressure of solvent $A$ above an ideal solution?

$P_A=\chi_A P_A^\circ$ . In ideal solutions, solvent vapor pressure scales with its mole fraction times the pure solvent's vapor pressure.
What is the defining feature of dipole-dipole intermolecular forces?

Attraction between permanent dipoles of polar molecules. Permanent partial charges in polar molecules align to create attractive forces between opposite ends.
What is the primary intermolecular interaction responsible for hydration shells around ions?

Ion-dipole interactions between ions and water dipoles. Water molecules orient their dipoles around ions, stabilizing them through electrostatic attractions in aqueous solutions.

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