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.
Question 1 Answer
Correct Answer: B
The gas with the weakest attractive forces between particles will also have the lowest boiling point (He).
Question 2 Answer
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.
Question 3 Answer
Correct Answer: A
Endothermic reactions have the heat on the left side and a positive ΔH. Reactions with an increase in entropy also have a positive ΔS. Because the reaction in choice (A) produces two moles of gas for each mole of solid, it would have a positive ΔS.
Question 4 Answer
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.
Question 5 Answer
Correct Answer: C
To determine what reactions can be expected to occur, we need to look at both half-reactions for each reaction. Since some of the half-reactions occurring appear to be going in the opposite direction of our standard reduction reactions, we need to reverse the sign of the E° of the reactions. Hence, a value of +0.52 V becomes −0.52 V, which indicates a reaction that will not spontaneously occur without added energy. The only reaction with a net E° that is positive is choice (C): E° = +0.41 + (−0.13) = +0.28 V. This reaction is thus highly likely occur with no other added energy or reagents.