Use this free practice quiz with 30 questions to review 12 Intermolecular Forces and States of Matter, test your knowledge, and prepare for your next test or exam.
Two molecular substances have similar molecular size and shape, but one is polar and the other is nonpolar. Identify the intermolecular attractions expected for each, then predict how their relative attractions would generally affect their boiling points and vapor pressures. Explain why your prediction is a trend rather than a guaranteed numerical ranking.
The halogens change from gases among the lighter members to liquid Br₂ and solid I₂ at room temperature. Use the trend in electron count and electron-cloud distortability to explain how changing dispersion forces can help account for this progression in physical state.
A student claims that NH₃ and CH₄ both form hydrogen bonds because each contains hydrogen. Evaluate the claim by applying the requirements for hydrogen bonding to both molecules. State what can be concluded about their dispersion forces and what cannot be concluded from hydrogen-bond eligibility alone.
When NaCl dissolves in water, water molecules interact with Na⁺ and Cl⁻. Classify the attraction between the ions and water, and explain why this classification does not mean that the water molecules' internal O–H bonds have been broken.
Two liquids are compared at the same temperature, and one has stronger attractions between its particles. Predict which liquid generally has the lower vapor pressure, then trace the reasoning from molecular escape to vapor–liquid equilibrium.
A liquid is heated first under a higher external pressure and then under a lower external pressure. For each case, predict how the boiling temperature changes and explain the prediction using the condition that defines boiling.
Two substances have molecules with the same kinds of intermolecular attractions, but one substance has larger molecules with more electrons. What can you reasonably predict about their dispersion forces? Is that information alone enough to guarantee which substance has the higher boiling point? Explain your reasoning.
A sample absorbs heat while melting at a fixed pressure, yet its temperature remains at the phase-change temperature. Explain where the added energy goes and why this observation does not imply that the sample's molecules are being chemically decomposed.
An open container of liquid produces some vapor even though the liquid is below its boiling temperature. Classify the process and explain why the presence of vapor alone does not show that the liquid is boiling.
A substance changes directly from solid to gas in one situation and directly from gas to solid in another. Name each process, state whether heat is absorbed or released in each, and explain whether these phase changes by themselves imply a change in chemical identity.
A phase diagram shows a point where the conditions for solid, liquid, and gas meet. Explain what coexistence means at this point and how it differs from a point on a boundary where two phases coexist.
A researcher extends a liquid–gas phase boundary on a diagram to conditions above its critical point and continues labeling separate liquid and gas regions. Explain what is wrong with this interpretation and what the critical point means for that boundary.
The halogens change from gases at room temperature among the smaller members to liquid Br₂ and solid I₂. Explain how a particle-level change accounts for this trend, including the intermolecular force involved and why it affects the observed phases.
A small polar molecule and a much larger nonpolar molecule are compared, but no further structural or property data are given. Can you reliably predict which has the higher boiling point from polarity alone? Explain the forces present and what additional considerations prevent a certain ranking.
Water has a comparatively high boiling point. Explain how its molecular attractions account for this, contrast them with the attractions in a comparable nonpolar liquid, and clarify whether boiling normally breaks the bonds within water molecules.
Two comparable liquids are at the same temperature and external pressure. Liquid X has stronger intermolecular attractions than liquid Y. Predict which has the lower vapor pressure at that temperature and which generally requires a higher temperature to boil; connect both predictions using the definitions of vapor pressure and boiling.
A liquid is boiled first at a certain external pressure and then at a lower external pressure. Predict how its boiling temperature changes and explain why. Then state what happens to the boiling temperature if the external pressure is raised instead.
A sample is heated at fixed pressure and its temperature remains constant while it melts. Explain where the added energy goes, why the temperature does not rise during this interval, and what further heating does after melting is complete.
In an open container, vapor is observed above a liquid whose temperature is below its boiling point, with no vaporization throughout the liquid. Explain which process is occurring and why the observation does not establish that the liquid is boiling.
A liquid has strong intermolecular attractions. Explain how those attractions can affect its viscosity and its surface tension, and distinguish what each property measures. Does a high value of one property, by itself, determine the value of the other?
A phase diagram marks both a triple point and a critical point. Explain what phases coexist at the triple point, what ends at the critical point, and what the diagram implies about distinguishing liquid from gas above the critical temperature and pressure.
A sample changes directly from gas to solid without passing through a liquid. Identify the phase change, determine whether heat is absorbed or released, and explain what happens to particle arrangement and chemical identity.
A substance is cooled from gas to liquid and then to solid. Compare particle spacing and motion in all three phases, explain how cooling affects average kinetic energy, and describe how the balance between motion and attractions relates to the phase changes.
A student claims that a substance’s melting and boiling temperatures are fixed values that can be predicted from temperature alone, regardless of surroundings. Use the information represented by a phase diagram to evaluate the claim and explain what conditions are needed to determine the stable phase.
Two substances are reported to differ in intermolecular attractions, but their molecular sizes and shapes are not provided. Assess whether the attraction information alone guarantees which has the higher measured boiling point. Explain the general trend and identify the structural factors that limit a certain prediction.
A sample of liquid water is vaporizing at a fixed pressure. Heat continues to enter while the temperature stays at the phase-change temperature. Explain how the added energy is used, why the temperature does not rise during this interval, and whether vaporization breaks the O–H bonds within the water molecules.
A sample contains dissolved Na⁺ and Cl⁻ ions in water. Identify the principal named intermolecular attraction between neighboring water molecules and the attraction between each dissolved ion and nearby water molecules. Also explain why these attractions are not the bonds within a water molecule.
A liquid in an open container loses some material to the air even though it is not boiling. Explain how this can happen. Then predict what lowering the surrounding pressure does to the temperature at which the liquid boils, and justify the prediction.
Two liquids are held at the same temperature in closed containers. Liquid A has stronger intermolecular attractions than Liquid B. Which liquid generally has the lower vapor pressure? Explain why, and give one reason this is a general trend rather than a rule based only on the types of intermolecular forces present.
The halogens in the sequence F₂ to I₂ experience dispersion forces, and their room-temperature phases progress from gases to liquid Br₂ and solid I₂. Explain how a change in electron-cloud properties accounts for this phase trend. Connect your explanation to how difficult it is for particles to separate.