# AP Chemistry: Multiple Choice Practice Questions

The multiple-choice section of the AP Chemistry test consists of 60 questions that you will have 90 minutes to answer. That’s an average of one and a half minutes per question. Refresh yourself on the general AP test strategies and multiple-choice strategies, then apply the concepts to the following five AP Chemistry practice questions.

Answer 1

Correct Answer: B

The gas with the weakest attractive forces between particles will also have the lowest boiling point (He).

Answer 2

Correct Answer: C

In nuclear chemistry, a sample of a radioactive substance is said to be critical, or have critical mass, when each fission process induces one other fission process to occur. If a radioactive substance is supercritical, each fission process starts more than one fission process. The radioactive sample need not be pure. Increasing the temperature has no effect on nuclear reaction rates. Although increasing the density of the fissile material (235U) could increase the efficiency of neutron capture, it is not required for the sample to be supercritical.

Answer 3

Correct Answer: A

Endothermic reactions have the heat on the left side and a positive Δ*H*. Reactions with an increase in entropy also have a positive Δ*S*. Because the reaction in choice (A) produces two moles of gas for each mole of solid, it would have a positive Δ*S*.

Answer 4

Correct Answer: D

Two half−lives occur in 14 minutes, thus (1/2)2 = 1/4 of the starting material remains, or 200 torr. Also, 600 torr of N2O5 have decomposed. For every two moles of N2O5 decomposed, seven moles total of N and O are produced or (600/2) × 7 = 2,100 torr. Because the partial pressures are additive, the total pressure would be 2,100 + 200 = 2,300 torr.