Ap chem 프린스턴 화학 summary part 3

Intermolecular Forces

Question 1:

Which intermolecular force is present between all molecules and atoms, and is the only IMF for nonpolar species?

(A) Hydrogen bonding
(B) Dipole–dipole interaction
(C) London dispersion forces
(D) Ion–dipole interaction

View Answer

Correct Answer: (C) London dispersion forces

Explanation: LDF arise from instantaneous/induced dipoles and act between all particles; they dominate in nonpolar substances.

Question 2:

Which substance has stronger London dispersion forces at the same temperature?

(A) F₂(g)
(B) I₂(s)
(C) Ne(g)
(D) CH₄(g)

View Answer

Correct Answer: (B) I₂(s)

Explanation: Larger electron clouds and higher polarizability increase LDF; iodine is the largest/polarizable among the choices.

Question 3:

Which molecule can form hydrogen bonds between its molecules?

(A) CH₃F
(B) CH₃NH₂
(C) H₂S
(D) CCl₄

View Answer

Correct Answer: (B) CH₃NH₂

Explanation: Hydrogen bonding requires H directly bonded to N, O, or F; methylamine has N–H bonds.

Question 4:

Which pure substance is expected to have the lowest vapor pressure at the same temperature?

(A) CO₂(s)
(B) H₂O(l)
(C) CCl₄(l)
(D) He(g)

View Answer

Correct Answer: (B) H₂O(l)

Explanation: Strong IMFs (hydrogen bonding) lower vapor pressure.

Question 5:

Which statement best compares LDF strength across the halogens at the same temperature?

(A) F₂ > Cl₂ > Br₂ > I₂
(B) I₂ > Br₂ > Cl₂ > F₂
(C) All identical due to similar valence electrons
(D) Cl₂ > I₂ > Br₂ > F₂

View Answer

Correct Answer: (B)

Explanation: LDF increase with electron count/polarizability: F₂ < Cl₂ < Br₂ < I₂.

Question 6:

What is the primary attractive force when O₂(g) dissolves in water?

(A) Dipole–dipole
(B) Ion–dipole
(C) Dipole–induced dipole
(D) Hydrogen bonding with O₂

View Answer

Correct Answer: (C) Dipole–induced dipole

Explanation: Polar H₂O induces a dipole in nonpolar O₂, leading to attraction.

Question 7:

As intermolecular forces strengthen for a liquid at fixed temperature, which property decreases?

(A) Boiling point
(B) Viscosity
(C) Vapor pressure
(D) Surface tension

View Answer

Correct Answer: (C) Vapor pressure

Explanation: Stronger IMFs retain molecules in the liquid, lowering vapor pressure (and volatility).

Question 8:

Which pair correctly ranks expected boiling points (highest to lowest) based on dominant IMFs?

(A) H₂O > CH₃OH > CH₃Cl > He
(B) He > CH₃Cl > CH₃OH > H₂O
(C) CH₃Cl > H₂O > CH₃OH > He
(D) CH₃OH > H₂O > CH₃Cl > He

View Answer

Correct Answer: (A)

Explanation: Strong H-bond network in water > alcohol H-bonding > polar dipole–dipole > LDF only.

Question 9:

A gas mixture at 1.00 atm contains 35.0% He by moles. What is the partial pressure of He?

(A) 0.150 atm
(B) 0.250 atm
(C) 0.350 atm
(D) 0.650 atm

View Answer

Correct Answer: (C) 0.350 atm

Explanation: Dalton’s Law: p_He = X_He · P_total = 0.350 × 1.00 atm = 0.350 atm.

Question 10:

A rigid container holds 2.0 mol N₂ and 1.0 mol O₂ at the same T. What is the ratio p(N₂):p(O₂)?

(A) 1:1
(B) 1:2
(C) 2:1
(D) 3:1

View Answer

Correct Answer: (C) 2:1

Explanation: For ideal gases in the same V and T, p ∝ n. So p(N₂):p(O₂) = 2.0:1.0.

Question 11:

Which is not an assumption of the Kinetic Molecular Theory for ideal gases?

(A) Particles are in constant random motion.
(B) Collisions are perfectly elastic.
(C) Particles exert attractive and repulsive forces on each other.
(D) Particle volume is negligible compared to container volume.

View Answer

Correct Answer: (C)

Explanation: Ideal gases are assumed to have no IMFs; (A), (B), and (D) are KMT assumptions.

Question 12:

At the same temperature, which statement is true for different ideal gases?

(A) All have the same average speed.
(B) All have the same average kinetic energy.
(C) Heavier gases have higher rms speeds.
(D) Lighter gases have lower most probable speeds.

View Answer

Correct Answer: (B)

Explanation: ⟨KE⟩ depends only on T; speeds depend on molar mass (lighter → faster).

Question 13:

Which gas has the highest rms speed at 298 K?

(A) He
(B) N₂
(C) Ar
(D) SF₆

View Answer

Correct Answer: (A) He

Explanation: v_rms ∝ √(T/M); the smallest molar mass (He) moves fastest at the same T.

Question 14:

Under which conditions does a real gas behave most ideally?

(A) Low T, high P
(B) High T, low P
(C) Low T, low P
(D) High T, high P

View Answer

Correct Answer: (B) High T, low P

Explanation: High T reduces IMF effects; low P makes particle volume negligible.

Question 15:

Which combination most increases deviations from ideal behavior?

(A) Low T and high P
(B) High T and low P
(C) Very low molar mass
(D) Large container volume

View Answer

Correct Answer: (A) Low T and high P

Explanation: Low T → IMFs matter; high P → finite particle volume matters.

Question 16:

How does the Maxwell–Boltzmann speed distribution change when temperature increases for a given gas?

(A) Peak shifts to lower speed and narrows
(B) Peak shifts to higher speed and broadens
(C) Peak height and position remain unchanged
(D) Distribution becomes symmetric about the mean

View Answer

Correct Answer: (B)

Explanation: Higher T → higher average/most probable speeds and a broader distribution.

Question 17:

According to Graham’s law, how many times faster does H₂ effuse than O₂ at the same T?

(A) 2
(B) 3
(C) 4
(D) 8

View Answer

Correct Answer: (C) 4

Explanation: Rate ∝ 1/√M; √(M_O2/M_H2) = √(32/2) = √16 = 4.

Question 18:

For a real gas at moderate high pressure, the measured pressure is often lower than ideal. The best explanation is:

(A) Particle volume increases collision frequency
(B) Attractive forces reduce momentum transfer on the walls
(C) Collisions are inelastic
(D) Temperature spontaneously decreases

View Answer

Correct Answer: (B)

Explanation: Intermolecular attractions pull particles inward, decreasing effective wall impacts.

Question 19:

At the same T and P, which ideal gas sample has the greatest density?

(A) He
(B) N₂
(C) O₂
(D) SF₆

View Answer

Correct Answer: (D) SF₆

Explanation: For ideal gases, ρ = PM/RT; at fixed P and T, density ∝ molar mass.

Question 20:

A sealed rigid container of an ideal gas is cooled from 350 K to 250 K. Which changes correctly describe the system?

(A) Pressure increases; average KE increases; most probable speed increases
(B) Pressure decreases; average KE decreases; most probable speed decreases
(C) Pressure unchanged; average KE unchanged; speed unchanged
(D) Pressure decreases; average KE unchanged; speed decreases

View Answer

Correct Answer: (B)

Explanation: In a rigid container, P ∝ T; kinetic energy and characteristic speeds scale with T.

Question 21:

Which substance exhibits dipole–dipole interactions (as a significant IMF) between its molecules?

(A) CH₂Cl₂
(B) CO₂
(C) CCl₄
(D) Xe

View Answer

Correct Answer: (A) CH₂Cl₂

Explanation: Dichloromethane is polar and shows dipole–dipole forces; the others are nonpolar and rely on LDF only.

Question 22:

Which order correctly ranks boiling points (highest to lowest) for the noble gases?

(A) He > Ne > Ar > Kr > Xe
(B) Xe > Kr > Ar > Ne > He
(C) Ne > He > Ar > Kr > Xe
(D) Ar > Xe > Kr > Ne > He

View Answer

Correct Answer: (B)

Explanation: Boiling point increases with molar mass/polarizability, strengthening LDF.

Question 23:

An ideal gas (n = 0.500 mol) in a 10.0 L rigid container at 300 K has what pressure (R = 0.0821 L·atm·mol⁻¹·K⁻¹)?

(A) 0.82 atm
(B) 1.23 atm
(C) 1.50 atm
(D) 2.46 atm

View Answer

Correct Answer: (B) 1.23 atm

Explanation: P = nRT/V = (0.500)(0.0821)(300)/10.0 ≈ 1.23 atm.

Question 24:

Hydrogen is collected over water at 25 °C. If the total pressure is 760 torr and the water vapor pressure is 24 torr, what is the partial pressure of H₂?

(A) 724 torr
(B) 736 torr
(C) 760 torr
(D) 784 torr

View Answer

Correct Answer: (B) 736 torr

Explanation: p(H₂) = P_tot − p(H₂O) = 760 − 24 = 736 torr.

Question 25:

At the same temperature, how many times faster does NH₃ effuse than CO₂?

(A) 1.2×
(B) 1.6×
(C) 2.0×
(D) 2.6×

View Answer

Correct Answer: (B) 1.6×

Explanation: Rate ∝ 1/√M; √(44/17) ≈ 1.61.

Question 26:

The compressibility factor Z = PV/(nRT) for a real gas at moderate pressure is often < 1. What is the best reason?

(A) Particle volume dominates
(B) Attractive forces lower the measured pressure
(C) Inelastic collisions reduce temperature
(D) R is not constant for real gases

View Answer

Correct Answer: (B)

Explanation: Attractions pull molecules inward, reducing wall impacts → P real < P ideal → Z < 1.

Question 27:

At the same T and P, which gas is expected to deviate most from ideal behavior?

(A) He
(B) CH₄
(C) CO₂
(D) NH₃

View Answer

Correct Answer: (D) NH₃

Explanation: Stronger IMFs (H-bonding capability) cause greater non-ideality than weakly interacting gases.

Question 28:

For gases at the same temperature, which statement about the Maxwell–Boltzmann distribution is correct?

(A) He has a narrower distribution than Ar
(B) He and Ar have identical distributions
(C) He has a broader distribution shifted to higher speeds
(D) Ar peaks at higher speed than He

View Answer

Correct Answer: (C)

Explanation: Lighter gases move faster on average and show broader speed distributions at the same T.

Question 29:

Which pair is best described by a dipole–induced dipole attraction?

(A) HCl (polar) and Ar (nonpolar)
(B) CO₂ and CH₄
(C) H₂O and H₂O
(D) Cl₂ and Cl₂

View Answer

Correct Answer: (A)

Explanation: A polar molecule (HCl) can induce a dipole in a nonpolar atom (Ar). (C) is H-bonding; (B,D) are LDF only.

Question 30:

What is the density of O₂(g) at STP (1 atm, 273 K)?

(A) 0.89 g·L⁻¹
(B) 1.00 g·L⁻¹
(C) 1.43 g·L⁻¹
(D) 2.86 g·L⁻¹

View Answer

Correct Answer: (C) 1.43 g·L⁻¹

Explanation: ρ = PM/RT = (1)(32)/(0.0821×273) ≈ 1.43 g·L⁻¹.

Question 31:

A gas has density 1.25 g·L⁻¹ at STP. What is its molar mass?

(A) 16 g·mol⁻¹
(B) 28 g·mol⁻¹
(C) 32 g·mol⁻¹
(D) 44 g·mol⁻¹

View Answer

Correct Answer: (B) 28 g·mol⁻¹

Explanation: M = ρRT/P = 1.25×(0.0821×273)/1 ≈ 28 g·mol⁻¹.

Question 32:

In a gas mixture, X_A = 0.60 and the total pressure is 1.50 atm. What is p_A?

(A) 0.60 atm
(B) 0.75 atm
(C) 0.90 atm
(D) 1.50 atm

View Answer

Correct Answer: (C) 0.90 atm

Explanation: p_A = X_A×P_tot = 0.60×1.50 = 0.90 atm.

Question 33:

At very high pressures, many real gases show Z > 1 mainly because:

(A) Attractions dominate and lower P
(B) Repulsions/finite particle volume dominate
(C) Temperature becomes non-constant
(D) R increases with pressure

View Answer

Correct Answer: (B)

Explanation: Excluded volume (repulsions) makes the gas less compressible than ideal → Z > 1.

Question 34:

Which ranking (strongest to weakest) of typical IMFs is generally correct for small molecules?

(A) LDF > H-bond > dipole–dipole
(B) H-bond > dipole–dipole > LDF
(C) Dipole–dipole > H-bond > LDF
(D) LDF = dipole–dipole = H-bond

View Answer

Correct Answer: (B)

Explanation: Hydrogen bonding is strongest, then dipole–dipole, then LDF (on a per-molecule basis).

Question 35:

Which has the higher boiling point at 1 atm, mainly due to greater surface area (stronger LDF)?

(A) Neopentane (2,2-dimethylpropane)
(B) n-Pentane
(C) Both the same
(D) Cannot be predicted

View Answer

Correct Answer: (B) n-Pentane

Explanation: Less compact isomers have greater contact area → stronger LDF → higher b.p.

Question 36:

At 298 K, which correctly orders most probable molecular speeds (highest to lowest)?

(A) Ar > Ne > He
(B) He > Ne > Ar
(C) Ne > He > Ar
(D) All equal at same T

View Answer

Correct Answer: (B) He > Ne > Ar

Explanation: Speeds scale as 1/√M; lighter gases move faster at the same temperature.

Question 37:

For an ideal gas at constant pressure, if the temperature (K) is doubled, the volume will:

(A) Halve
(B) Remain the same
(C) Double
(D) Quadruple

View Answer

Correct Answer: (C) Double

Explanation: Charles’s law: V ∝ T at constant P and n.

Question 38:

For an ideal gas at constant temperature, compressing the volume to one-half will cause the pressure to:

(A) Halve
(B) Stay constant
(C) Double
(D) Quadruple

View Answer

Correct Answer: (C) Double

Explanation: Boyle’s law: P ∝ 1/V at constant T and n.

Question 39:

Which pair experiences only London dispersion forces between molecules?

(A) N₂ and CH₄
(B) HCl and H₂O
(C) NH₃ and HF
(D) CH₃Cl and CH₃CH₂OH

View Answer

Correct Answer: (A)

Explanation: N₂ and CH₄ are nonpolar; interactions are LDF. The others have permanent dipoles and/or H-bonding.

Question 40:

Oxygen is collected over water at 25 °C. If the total pressure is 755 torr and p(H₂O) = 24 torr, what is p(O₂)?

(A) 731 torr
(B) 751 torr
(C) 755 torr
(D) 779 torr

View Answer

Correct Answer: (A) 731 torr

Explanation: Dalton’s law: p(O₂) = 755 − 24 = 731 torr.

Question 41:

At 25 °C, which liquid has the higher vapor pressure?

(A) Hexane (C₆H₁₄)
(B) Octane (C₈H₁₈)
(C) They are the same
(D) Cannot be determined

View Answer

Explanation: Weaker IMFs → higher vapor pressure. Hexane has fewer electrons and weaker LDF than octane.

Correct Answer: (A) Hexane

Question 42:

Which pure substance shows hydrogen bonding between identical molecules?

(A) CH₃F
(B) HF
(C) H₂S
(D) CH₃OCH₃ (dimethyl ether)

View Answer

Explanation: Hydrogen bonding requires H directly bonded to N, O, or F. Only HF meets this in the pure substance.

Correct Answer: (B) HF

Question 43:

Which liquid is expected to have the highest viscosity at room temperature?

(A) Hexane
(B) Water
(C) Ethanol
(D) Glycerol (C₃H₈O₃)

View Answer

Explanation: Glycerol can form multiple hydrogen bonds per molecule, greatly increasing viscosity.

Correct Answer: (D) Glycerol

Question 44:

Capillary rise is greatest for which pair?

(A) Water in glass
(B) Mercury in glass
(C) Hexane in PTFE (Teflon)
(D) Bromine in glass

View Answer

Explanation: Strong adhesive forces between water and glass plus H-bonding → strong capillarity. Mercury shows depression (concave-down meniscus).

Correct Answer: (A) Water in glass

Question 45:

Which gas has the highest root-mean-square (rms) speed at 298 K?

(A) H₂
(B) He
(C) N₂
(D) O₂

View Answer

Explanation: \(u_{\text{rms}}\propto \sqrt{T/M}\). The smallest molar mass (H₂) gives the highest speed at the same T.

Correct Answer: (A) H₂

Question 46:

Approximate the rms speed of N₂(g) at 300 K. (Use \(u_{\text{rms}}=\sqrt{3RT/M}\), R = 8.314 J·mol⁻¹·K⁻¹, M = 0.028 kg·mol⁻¹)

(A) 290 m·s⁻¹
(B) 400 m·s⁻¹
(C) 517 m·s⁻¹
(D) 870 m·s⁻¹

View Answer

Calculation: \(\sqrt{(3)(8.314)(300)/0.028}\approx 5.17\times10^{2}\) m·s⁻¹.

Correct Answer: (C) 517 m·s⁻¹

Question 47:

A mixture has 2.0 mol N₂ and 1.0 mol O₂. If total pressure is 900 torr, what is the partial pressure of N₂?

(A) 300 torr
(B) 450 torr
(C) 600 torr
(D) 900 torr

View Answer

Calculation: \(\chi_{\text{N2}}=2/3\); \(P_{\text{N2}}=\chi P_{\text{tot}}=(2/3)(900)=600\) torr.

Correct Answer: (C) 600 torr

Question 48:

A 2.00 L rigid flask at 27 °C contains 0.080 mol of an ideal gas. What is the pressure?

(A) 0.49 atm
(B) 0.74 atm
(C) 0.98 atm
(D) 1.6 atm

View Answer

Calculation: \(P=\dfrac{nRT}{V}=\dfrac{(0.080)(0.0821)(300)}{2.00}\approx0.985\) atm.

Correct Answer: (C) 0.98 atm

Question 49:

A gas at 0.80 atm, 3.00 L, and 300 K is compressed to 1.50 L and cooled to 200 K. What is the new pressure?

(A) 0.53 atm
(B) 0.80 atm
(C) 1.07 atm
(D) 1.60 atm

View Answer

Calculation: \(P_2=P_1\frac{V_1}{V_2}\frac{T_2}{T_1}=0.80\cdot\frac{3.00}{1.50}\cdot\frac{200}{300}\approx1.07\) atm.

Correct Answer: (C) 1.07 atm

Question 50:

Under which conditions do real gases behave most ideally?

(A) Low T, high P, strong IMFs
(B) Low T, low P, strong IMFs
(C) High T, low P, weak IMFs, small molar mass
(D) High T, high P, strong IMFs

View Answer

Explanation: High T minimizes attractions; low P makes particle volume negligible; weak IMFs and small M also help.

Correct Answer: (C)

Question 51:

Which halogen molecule has the strongest London dispersion forces?

(A) F₂
(B) Cl₂
(C) Br₂
(D) I₂

View Answer

Explanation: LDF increase with electron count/polarizability. I₂ is largest.

Correct Answer: (D) I₂

Question 52:

Which compound has the highest normal boiling point?

(A) CH₄
(B) CH₃CHO (acetaldehyde)
(C) CH₃OCH₃ (dimethyl ether)
(D) CH₃CH₂OH (ethanol)

View Answer

Explanation: Ethanol can donate and accept H-bonds; the others cannot donate H-bonds.

Correct Answer: (D) Ethanol

Question 53:

When temperature increases for a gas, the Maxwell–Boltzmann speed distribution:

(A) Peaks higher and narrows
(B) Shifts to higher speeds and broadens
(C) Shifts to lower speeds and broadens
(D) Does not change

View Answer

Explanation: Higher T → higher average speed, broader distribution, lower peak height.

Correct Answer: (B)

Question 54:

Graham’s law: What is the effusion rate ratio \(r_{\text{He}}/r_{\text{O2}}\) at the same T and P?

(A) 0.35
(B) 1.9
(C) 2.8
(D) 4.0

View Answer

Calculation: \(r\propto 1/\sqrt{M}\) so \(r_{\text{He}}/r_{\text{O2}}=\sqrt{32/4}=\sqrt{8}\approx2.8\).

Correct Answer: (C) 2.8

Question 55:

In the van der Waals equation, which parameter primarily corrects for intermolecular attractions?

(A) a
(B) b
(C) R
(D) T

View Answer

Explanation: The constant a reduces effective pressure due to attractions; b corrects for finite molecular volume.

Correct Answer: (A) a

Question 56:

Two different ideal gases are in the same container at the same temperature. Which statement is true?

(A) The lighter gas has greater average kinetic energy
(B) Both gases have the same average kinetic energy
(C) The heavier gas has greater average kinetic energy
(D) Average kinetic energy depends on molar mass, not temperature

View Answer

Explanation: \(\overline{KE}=\tfrac{3}{2}RT\); depends only on T for ideal gases.

Correct Answer: (B)

Question 57:

At 25 °C, which has the higher vapor pressure?

(A) Water
(B) Acetone ((CH₃)₂CO)
(C) They are equal
(D) Not enough information

View Answer

Explanation: Acetone cannot donate H-bonds between its own molecules; weaker IMFs → higher vapor pressure than water.

Correct Answer: (B) Acetone

Question 58:

Which sample contains the greatest number of gas molecules?

(A) 2.0 L at 1.0 atm and 300 K
(B) 1.0 L at 2.0 atm and 300 K
(C) 3.0 L at 0.80 atm and 400 K
(D) 1.5 L at 1.2 atm and 350 K

View Answer

Calculation: \(n=\dfrac{PV}{RT}\). A: \(2.0/300\); B: \(2.0/300\) (tie); C: \(2.4/400\) (smaller); D: \(1.8/350\) (smaller).

Correct Answer: (A) and (B) (tie)

Question 59:

Which gas has the greater average speed at the same temperature?

(A) SO₂
(B) CO
(C) CO₂
(D) H₂S

View Answer

Explanation: At the same T, lighter gases move faster on average. CO (M ≈ 28) is lighter than SO₂, CO₂, and H₂S.

Correct Answer: (B) CO

Question 60:

Which statement about volatility, vapor pressure, and IMFs is correct at a fixed temperature?

(A) Stronger IMFs → higher vapor pressure → higher boiling point
(B) Weaker IMFs → higher vapor pressure → lower boiling point
(C) Stronger IMFs → higher vapor pressure → lower boiling point
(D) Vapor pressure is independent of IMFs

View Answer

Explanation: Weak IMFs make molecules escape more easily, increasing vapor pressure and lowering the boiling point.

Correct Answer: (B)

Ap chem 프린스턴 화학 summary part 3

Intermolecular Forces

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