Potential, Free Energy, and Equilibrium Quiz
The question sheet
Reveal any answer as you study-
What was defined as the maximum work that could be performed by a system?
- Cell potential, E°cell
- Faraday's constant, F
- Equilibrium constant, K
- Standard free energy change, ΔG°
Reveal answer
Answer: Standard free energy change, ΔG°
Source evidence
PDF page 921: The standard free energy change of a process, ΔG°, was defined in a previous chapter as the maximum work that could be performed by a system, wmax. In the case of a redox reaction taking place within a galvanic cell under standard state conditions, essentially all the work is associated with transferring the electrons from reductant-to-oxidant, welec:
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Which equation correctly relates ΔG° to standard cell potential?
- ΔG° = nF/E°cell
- ΔG° = −RT ln E°cell
- ΔG° = −nFE°cell
- ΔG° = nFE°cell
Reveal answer
Answer: ΔG° = −nFE°cell
Source evidence
PDF page 921: elec The work associated with transferring electrons is determined by the total amount of charge (coulombs) transferred and the cell potential: ° ΔG° = w = −nFE elec cell ° ΔG° = −nFE cell where n is the number of moles of electrons transferred, F is Faraday’s constant, and E°cell is the standard cell potential. The relation between free energy change and standard cell potential confirms the sign conventions and spontaneity criteria previously discussed for both of these properties: spontaneous redox reactions exhibit positive potentials and negative free energy changes.
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In ΔG° = −nFE°cell, what does n represent?
- Number of half-cells
- Number of coulombs transferred
- Number of moles of electrons transferred
- Number of product molecules
Reveal answer
Answer: Number of moles of electrons transferred
Source evidence
PDF page 921: elec The work associated with transferring electrons is determined by the total amount of charge (coulombs) transferred and the cell potential: ° ΔG° = w = −nFE elec cell ° ΔG° = −nFE cell where n is the number of moles of electrons transferred, F is Faraday’s constant, and E°cell is the standard cell potential. The relation between free energy change and standard cell potential confirms the sign conventions and spontaneity criteria previously discussed for both of these properties: spontaneous redox reactions exhibit positive potentials and negative free energy changes.
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Spontaneous redox reactions exhibit which combination?
- Positive potential, positive ΔG
- Negative potential, positive ΔG
- Negative potential, negative ΔG
- Positive potential, negative ΔG
Reveal answer
Answer: Positive potential, negative ΔG
Source evidence
PDF page 921: elec The work associated with transferring electrons is determined by the total amount of charge (coulombs) transferred and the cell potential: ° ΔG° = w = −nFE elec cell ° ΔG° = −nFE cell where n is the number of moles of electrons transferred, F is Faraday’s constant, and E°cell is the standard cell potential. The relation between free energy change and standard cell potential confirms the sign conventions and spontaneity criteria previously discussed for both of these properties: spontaneous redox reactions exhibit positive potentials and negative free energy changes.
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Which relation combines ΔG° with K and E°cell?
- ΔG° = RT ln K = nFE°cell
- ΔG° = −RT/K = −nFE°cell
- ΔG° = RT/K = nF/E°cell
- ΔG° = −RT ln K = −nFE°cell
Reveal answer
Answer: ΔG° = −RT ln K = −nFE°cell
Source evidence
PDF page 921: ΔG° = −RT ln K = −nFE
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Redox reactions with large positive E°cell values will:
- Proceed far towards completion
- Not reach equilibrium
- Remain at initial composition
- Favor reactants at equilibrium
Reveal answer
Answer: Proceed far towards completion
Source evidence
PDF page 921: cell ° ⎛RT ⎞ E = ln K cell ⎝nF ⎠ This equation indicates redox reactions with large (positive) standard cell potentials will proceed far towards completion, reaching equilibrium when the majority of reactant has been converted to product. A summary of the relations between E°, ΔG° and K is depicted in Figure 17.7, and a table correlating reaction spontaneity to values of these properties is provided in Table 17.2.
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When K > 1, the values of ΔG° and E°cell are:
- ΔG° > 0, E°cell < 0
- ΔG° < 0, E°cell > 0
- ΔG° < 0, E°cell < 0
- ΔG° > 0, E°cell > 0
Reveal answer
Answer: ΔG° < 0, E°cell > 0
Source evidence
PDF page 922: K ΔG° E°cell > 1 < 0 > 0 Reaction is spontaneous under standard conditions Products more abundant at equilibrium
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When K < 1, the reaction under standard conditions is:
- Non-spontaneous
- Complete
- Spontaneous
- At equilibrium
Reveal answer
Answer: Non-spontaneous
Source evidence
PDF page 922: < 1 > 0 < 0 Reaction is non-spontaneous under standard conditions Reactants more abundant at equilibrium
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When ΔG° = 0 and E°cell = 0, the value of K is:
- Equal to zero
- Greater than 1
- Less than 1
- Equal to 1
Reveal answer
Answer: Equal to 1
Source evidence
PDF page 922: = 1 = 0 = 0 Reaction is at equilibrium under standard conditions Reactants and products equally abundant
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When a reaction is at equilibrium under standard conditions, reactants and products are:
- Reactants more abundant
- Equally abundant
- Products more abundant
- Fully converted
Reveal answer
Answer: Equally abundant
Source evidence
PDF page 922: = 1 = 0 = 0 Reaction is at equilibrium under standard conditions Reactants and products equally abundant
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For 2Ag+ + Fe ⇌ 2Ag + Fe2+, what standard cell potential was calculated?
- +0.7996 V
- +0.291 V
- +1.247 V
- −0.447 V
Reveal answer
Answer: +1.247 V
Source evidence
PDF page 922: 2+ − = −0.447 V anode (oxidation): Fe(s) ⟶ Fe (aq) + 2e E° 2+ Fe /Fe + − = 0.7996 V cathode (reduction): 2 × (Ag (aq) + e ⟶ Ag(s)) E° + Ag /Ag E° = E° − E° = = +1.247 V E° + − E° 2+ cell cathode anode Ag /Ag Fe /Fe With n = 2, the equilibrium constant is then
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For 2Ag+ + Fe ⇌ 2Ag + Fe2+, the equilibrium constant K was approximately:
- 10^0.0592
- 10^-42
- 10^2
- 10^42
Reveal answer
Answer: 10^42
Source evidence
PDF page 923: 0.0592 V E° = log K cell n n × E° /0.0592 V cell K = 10 2 × 1.247 V/0.0592 V K = 10 42.128 K = 10 42
Chemistry 2e
Chemistry 2e by OpenStax, used under CC BY 4.0. Changes made by Stratacademy.
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