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Which of the following changes will cause the free energy of a cell reaction to decrease? \( \boldsymbol{Z} \boldsymbol{n} \mid \boldsymbol{Z} \boldsymbol{n} \boldsymbol{S} \boldsymbol{O}_{4}(\boldsymbol{a} \boldsymbol{q})\left(\boldsymbol{x}_{1} \boldsymbol{M}\right) \| \boldsymbol{H} \boldsymbol{C l}(\boldsymbol{a} \boldsymbol{q})\left(\boldsymbol{x}_{2} \boldsymbol{N}\right. \) This question has multiple correct options

1. Increase in the volume of HCI solution from \( 100 \mathrm{mL} \) to \( 200 \mathrm{mL} \)
2. Increase in the pressure of hydrogen from 1 atm to 2 \( \operatorname{atm} \)
3. Increase in molarity \( x_{2} \) from 0.1 to 1 M
4. Decrease in molarity \( x_{1} \) from 1 M to 0.1 M

Correct answer: Increase in molarity \( x_{2} \) from 0.1 to 1 M

Solution

For a galvanic cell, \(\Delta G=-nFE\), so free energy decreases when the cell potential increases. Raising the HCl concentration increases the cathode-side \([H^+]\), which increases \(E\) and makes \(\Delta G\) more negative.

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