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AP Chemistry MCQs

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AP Chemistry practice questions by unit

Fiveable has 27,339 AP Chemistry multiple-choice practice questions across 9 units, plus 442 stimulus-based question sets built around a source. Practice one unit or topic at a time.

  • Unit 1 – Atomic Structure & Properties: 1,893 multiple-choice questions, 37 stimulus sets
  • Unit 2 – Compound Structure and Properties: 1,506 multiple-choice questions, 35 stimulus sets
  • Unit 3 – Properties of Substances and Mixtures: 2,810 multiple-choice questions, 70 stimulus sets
  • Unit 4 – Chemical Reactions: 2,369 multiple-choice questions, 38 stimulus sets
  • Unit 5 – Kinetics: 3,494 multiple-choice questions, 52 stimulus sets
  • Unit 6 – Thermochemistry: 3,306 multiple-choice questions, 44 stimulus sets
  • Unit 7 – Equilibrium: 4,074 multiple-choice questions, 42 stimulus sets
  • Unit 8 – Acids & Bases: 3,993 multiple-choice questions, 62 stimulus sets
  • Unit 9 – Thermodynamics and Electrochemistry: 3,894 multiple-choice questions, 62 stimulus sets

Sample AP Chemistry practice question

A heating curve plots temperature versus heat added for a pure substance. The horizontal segment representing vaporization is significantly longer than the horizontal segment representing melting. Which conclusion about the standard entropy of vaporization (ΔS°vap) compared to the standard entropy of fusion (ΔS°fus) is best supported by this graphical difference?

ΔS°vap > ΔS°fus because the gas phase has greater matter dispersal than the liquid.

Correct answer

ΔS°vap < ΔS°fus because the higher temperature reduces the calculated entropy change.

ΔS°vap = ΔS°fus because the mass of the substance remains constant during heating.

ΔS°vap ≈ 0 because the temperature remains constant throughout the phase transition.

Explanation

Interpreting the graph shows that vaporization requires more energy (longer segment) than fusion. Since ΔS = q/T, the large heat input combined with the massive increase in disorder (dispersal of matter) when forming a gas results in ΔS°vap being significantly larger than ΔS°fus.

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