The Nernst Equation: Quiz

The Nernst Equation: Quiz

7 questions

1. Question 1EasyAs a galvanic cell discharges, what happens to Q and E?

   AQ increases, E increasesBQ increases, E decreasesCQ decreases, E decreasesDBoth stay constant
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   Answer: Q increases, E decreases

   Products accumulate, so Q rises; by the Nernst equation E = E° − (0.0592/n) log Q, E falls until it reaches zero at equilibrium.

2. Question 2EasyWhat is the cell potential when the cell reaction is at equilibrium?

   AE°B0 VC1.00 VDIt becomes negative
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   Answer: 0 V

   At equilibrium Q = K, there is no driving force and E = 0: the battery is flat.

3. Question 3MediumFor Zn + Cu²⁺ → Zn²⁺ + Cu (E° = 1.10 V), what is E when [Zn²⁺] = 1.0 M and [Cu²⁺] = 0.010 M?

   A1.16 VB1.10 VC1.04 VD0.98 V
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   Answer: 1.04 V

   Q = 1.0 ÷ 0.010 = 100; E = 1.10 V − (0.0592 V ÷ 2) × log 100 = 1.10 V − 0.0592 V = 1.04 V.

4. Question 4MediumA silver concentration cell has [Ag⁺] = 0.0010 M on one side and 0.10 M on the other. What is E at 25 °C? (n = 1)

   A0.0592 VB0.118 VC0.80 VD0 V
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   Answer: 0.118 V

   E° = 0; Q = 0.0010 ÷ 0.10 = 0.010; E = 0 − 0.0592 V × log(0.010) = +0.118 V.

5. Question 5MediumA reaction has E° = 0.46 V and n = 2. What is ΔG°?

   A−44.4 kJ/molB−88.8 kJ/molC+88.8 kJ/molD−0.92 kJ/mol
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   Answer: −88.8 kJ/mol

   ΔG° = −nFE° = −2 × 96 485 C/mol × 0.46 V = −88 770 J/mol = −88.8 kJ/mol.

6. Question 6HardFor E° = 0.46 V and n = 2 at 25 °C, what is K?

   A1.0 × 10⁰B3.5 × 10⁷C3.5 × 10¹⁵D5.9 × 10⁻¹⁶
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   Answer: 3.5 × 10¹⁵

   log K = 2 × 0.46 ÷ 0.0592 = 15.54, so K = 10¹⁵·⁵⁴ = 3.5 × 10¹⁵. 3.5 × 10⁷ forgets n = 2.

7. Question 7HardA reaction has K = 1.0 × 10⁵ and n = 1 at 25 °C. What is E°?

   A0.30 VB0.059 VC−0.30 VD5.0 V
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   Answer: 0.30 V

   E° = (0.0592 V ÷ n) × log K = 0.0592 V × 5.0 = 0.296 V ≈ 0.30 V. K greater than 1 means E° is positive.