MCAT Chemical and Physical Foundations of Biological Systems Flashcards: 5b Intermolecular Forces Physical Properties

What this deck covers

This deck focuses on 5b Intermolecular Forces Physical Properties, giving you a quick way to review the definitions, rules, and examples that matter most for MCAT Chemical and Physical Foundations of Biological Systems.

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Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: Which species most commonly serves as a hydrogen-bond acceptor in neutral molecules?

Answer: 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.

Flashcard 2: Which option is more soluble in water: a polar solute or a nonpolar solute?

Answer: 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".

Flashcard 3: Identify the correct osmotic pressure formula for a dilute solution.

Answer: $\Pi=iMRT$. Osmotic pressure follows a relation analogous to the ideal gas law, based on effective molarity and temperature.

Flashcard 4: Identify the correct boiling point elevation formula for a solution.

Answer: $\Delta T_b=iK_b m$. Elevation is a colligative effect proportional to particle molality and the solvent's boiling constant $K_b$.

Flashcard 5: Identify the correct freezing point depression formula for a nonelectrolyte solution.

Answer: $\Delta T_f=iK_f m$. Colligative depression depends on effective particle concentration ($i m$) and the solvent-specific constant $K_f$.

Flashcard 6: What is Raoult's law for the vapor pressure of solvent $A$ above an ideal solution?

Answer: $P_A=\chi_A P_A^\circ$. In ideal solutions, solvent vapor pressure scales with its mole fraction times the pure solvent's vapor pressure.

Flashcard 7: What is the formula for mole fraction of component $A$, $\chi_A$?

Answer: $\chi_A=\frac{n_A}{\sum n_i}$. Mole fraction represents the proportional contribution of a component to the total moles in a mixture.

Flashcard 8: What is the formula for molality, $m$?

Answer: $m=\frac{\text{mol solute}}{\text{kg solvent}}$. Molality uses solvent mass, providing a temperature-independent concentration measure for colligative properties.

Flashcard 9: What is the formula for molarity, $M$?

Answer: $M=\frac{\text{mol solute}}{\text{L solution}}$. Molarity quantifies solute concentration based on total solution volume, useful for volumetric calculations.

Flashcard 10: What is the correct relation between boiling point and vapor pressure at $1\ \text{atm}$?

Answer: 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.

Flashcard 11: What is the correct phase-change relation between $\Delta H_{sub}$, $\Delta H_{fus}$, and $\Delta H_{vap}$?

Answer: $\Delta H_{sub}=\Delta H_{fus}+\Delta H_{vap}$. Sublimation combines the processes of fusion and vaporization in a single solid-to-gas transition.

Flashcard 12: What is the relationship between intermolecular force strength and enthalpy of vaporization, $ $\Delta H_{vap}$?

Answer: Stronger intermolecular forces increase $\Delta H_{vap}$. More energy is needed to overcome stronger attractions when transitioning from liquid to gas.

Flashcard 13: What is the relationship between intermolecular force strength and surface tension?

Answer: Stronger intermolecular forces increase surface tension. Stronger cohesive forces pull surface molecules inward, minimizing surface area and increasing tension.

Flashcard 14: What is the relationship between intermolecular force strength and viscosity?

Answer: Stronger intermolecular forces increase viscosity. Increased attractions hinder molecular flow, making the liquid more resistant to deformation.

Flashcard 15: What is the relationship between intermolecular force strength and vapor pressure at a given $T$?

Answer: Stronger intermolecular forces decrease vapor pressure. Stronger forces retain more molecules in the liquid, reducing evaporation rate at a fixed temperature.

Flashcard 16: What is the relationship between intermolecular force strength and boiling point?

Answer: Stronger intermolecular forces increase boiling point. Greater attractions require more thermal energy to separate molecules into the gas phase.

Flashcard 17: What is the primary intermolecular interaction responsible for hydration shells around ions?

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

Flashcard 18: What is the defining feature of ion-dipole forces in solutions?

Answer: 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.

Flashcard 19: What is the correct ranking of intermolecular forces from weakest to strongest?

Answer: 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.

Flashcard 20: What is the defining feature of London dispersion forces between atoms or molecules?

Answer: Attractive forces from instantaneous and induced dipoles. Fluctuating electron distributions create temporary dipoles that induce similar dipoles in nearby molecules, leading to weak attractions.

Flashcard 21: What molecular property most directly increases London dispersion forces in a series?

Answer: Greater polarizability (larger electron cloud; higher molar mass). Larger, more distortable electron clouds enhance temporary dipole formation and strength of induced attractions.

Flashcard 22: Which structural change increases London dispersion forces: more branching or less branching?

Answer: Less branching (greater surface area) increases dispersion forces. Straighter chains provide more surface area for contact, strengthening induced dipole interactions.

Flashcard 23: What is the defining feature of dipole-dipole intermolecular forces?

Answer: Attraction between permanent dipoles of polar molecules. Permanent partial charges in polar molecules align to create attractive forces between opposite ends.

Flashcard 24: What specific requirement must be met for hydrogen bonding to occur between molecules?

Answer: 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.

Flashcard 25: Which atoms can serve as the hydrogen-bond donor atom directly bonded to H?

Answer: N, O, or F. These highly electronegative atoms polarize the H-X bond sufficiently for strong hydrogen bond formation.