AP Chemistry Unit 9.9: Cell Potential and Free Energy

Practice AP Chemistry Unit 9.9 questions on calculating cell potential from half-reactions and relating its sign to ΔG° and favorability.

Covered syllabus points

9.9.A—Explain whether an electrochemical cell is thermodynamically favored, based on its standard cell potential and…

[Maximum number: 1]

A scientist constructs a galvanic cell as shown in the diagram. As the cell operates, the $\mathrm{Zn}(s)$

electrode increases in mass and the $\mathrm{Al}(s)$ electrode decreases in mass. A data table with the

standard reduction potentials for the substances follows the diagram.

Figure for Question 9.9 Cell Potential and Free Energy question 1 — AP Chemistry

Table for Question 9.9 Cell Potential and Free Energy question 1 — AP Chemistry

The standard Zn/Al cell has a value of $E_{\text {cell }}^{\circ}$ equal to 0.90 V. The scientist needs a galvanic cell

that produces a greater voltage. The scientist has access to the chemical systems in the table.

If the scientist uses the Zn half-cell and one of the other options from the table, what is the

MAXIMUM voltage that could be generated at standard conditions?

D For the correct calculated value.

Point 04

Examples of acceptable responses may include the following:

- $E_{\text {cell }}^{\circ}=1.50 \mathrm{~V}+0.76 \mathrm{~V}=2.26 \mathrm{~V}$

- $\mathrm{Au}^{3+}(a q)+3 e^{-} \rightarrow \mathrm{Au}(s)+1.50 \mathrm{~V}$ $\mathrm{Zn}(s) \rightarrow \mathrm{Zn}^{2+}(a q)+2 e^{-} \quad+0.76 \mathrm{~V}$ $E_{\text {cell }}^{\circ}=2.26 \mathrm{~V}$

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Covered syllabus points

9.9 Cell Potential and Free Energy question 1