AP Chemistry Unit 9 Progress Check: MCQ Exam Questions And Answers 2025

AP Chemistry Unit 9 Progress Check: MCQ Exam Questions And Answers 2025 Based on the information given, which of the following is a major difference between the zinc-mercury cell and the lithium-iodine cell? - Correct Answer B. During the initial cell operation, each reaction is thermodynamically favorable, but the larger operating potential of the lithium-iodine cell indicates that its cell reaction is more thermodynamically favorable. On average, after one year of operation, the potential of a lithium-iodine cell decreases by 1%-2%. Which of the following best helps to explain the cause for the decrease in cell potential? - Correct Answer D. Ecell=E°cell−RT/nF lnQ, and as the cell operates, Q increases. The use of zinc-mercury cells in hearing aids has been replaced by zinc-air cells that operate using the oxidation of Zn by O2 from the air, generating a potential of +1.60V. Table 2 provides the standard reduction potentials for the half-reactions used in zinc-mercury and zinc-air cells. Which of the following best explains the modification to the cell design that is mostly responsible for the difference in standard cell potentials for zinc-mercury and zinc-air cells? - Correct Answer A. The greater standard cell potential of the Zn-air cell compared to that of the zinc-mercury cell most likely results from the thermodynamically more favorable reduction of O2 compared to HgO.