Intermolecular forces test with answers for AP Chemistry (free PDF download)

Quick answer: Intermolecular forces are the attractions between separate particles of a substance. This AP Chemistry test on intermolecular forces has 8 questions worth 20 marks, to do in 45 minutes: naming forces, boiling point trend and vapour pressure. The mark scheme is on a separate page; free printable PDF.

This test lasts 45 minutes and is worth 20 points. Answer all questions, show your working for calculations and use the correct units. For explanations, name the intermolecular force and compare its strength.

Level: AP Chemistry · Curriculum: AP Chem Unit 3

Time: 45 minutes · 8 questions · Total: 20 marks · Calculator allowed

Contents

Question 1 Naming forces (2 marks)

Name the strongest intermolecular force in liquid CH₃OH and in liquid CH₃Cl.

Question 2 Boiling point trend (3 marks)

The boiling points of Cl₂, Br₂ and I₂ are −34 °C, 59 °C and 184 °C.

Name the force acting between the molecules. (1 mark)
Explain the trend. (2 marks)

Question 3 Vapour pressure (3 marks)

A liquid in a closed container.

The diagram shows a liquid in a closed flask at 25 °C.

State what is meant by equilibrium vapour pressure. (2 marks)
Explain what happens to the vapour pressure when the temperature rises to 40 °C. (1 mark)

Question 4 Ethanol and ethoxyethane (3 marks)

Ethanol (C₂H₅OH) boils at 78 °C and ethoxyethane (C₂H₅OC₂H₅) boils at 35 °C although it is heavier (74.1 g/mol against 46.1 g/mol). Explain why.

Question 5 Clausius–Clapeyron (3 marks)

A liquid has ΔH_vap = 30.0 kJ/mol and vapour pressure of 20.0 kPa at 300 K. Calculate its vapour pressure at 320 K (R = 8.314 J/(mol·K)).

Question 6 Types of solid (2 marks)

Classify solid silicon dioxide (quartz) and solid iodine, and explain why one melts above 1700 °C and the other near 114 °C.

Question 7 Altitude cooking (2 marks)

Explain why a pressure cooker cooks food faster than an open pan.

Question 8 Rank three liquids (2 marks)

Three liquids for comparison.

The molar masses are 58.1, 58.1 and 46.1 g/mol. Rank A, B and C in order of increasing boiling point and justify.

What are intermolecular forces? — Attractions between separate particles, weaker than covalent bonds.

Which force acts between all particles? — London dispersion forces.

Condition for hydrogen bonding? — H bonded to N, O or F, plus a lone pair nearby.

What makes dispersion forces stronger? — More electrons, larger and more polarisable cloud.

Effect of branching on boiling point? — Lowers it (less surface contact).

Define normal boiling point. — Temperature where vapour pressure equals 101.3 kPa.

Clausius–Clapeyron equation? — ln(P₂/P₁) = (ΔHvap/R)(1/T₁ − 1/T₂)

Value of R for this equation? — 8.314 J/(mol·K)

Which solids conduct when molten but not solid? — Ionic solids.

What does stronger IMF do to vapour pressure? — Lowers it at a given temperature.