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Questions and Answers
What condition is indicated by the degree symbol (°), when used with standard cell potential (E°)?
What condition is indicated by the degree symbol (°), when used with standard cell potential (E°)?
- Variable temperature and pressure
- Ideal gas conditions
- Standard conditions at 25°C (correct)
- Non-standard conditions
A voltaic cell is set up with a zinc electrode in a $Zn^{2+}$ solution and a copper electrode in a $Cu^{2+}$ solution. Given that the standard reduction potential for $Zn^{2+}$ is -0.76V and for $Cu^{2+}$ is +0.34V, what is the standard cell potential (E°) for this voltaic cell?
A voltaic cell is set up with a zinc electrode in a $Zn^{2+}$ solution and a copper electrode in a $Cu^{2+}$ solution. Given that the standard reduction potential for $Zn^{2+}$ is -0.76V and for $Cu^{2+}$ is +0.34V, what is the standard cell potential (E°) for this voltaic cell?
- -1.10 V
- 0.42 V
- 1.10 V (correct)
- -0.42 V
For a redox reaction to be spontaneous, what must be the sign of the overall standard cell potential (E°)?
For a redox reaction to be spontaneous, what must be the sign of the overall standard cell potential (E°)?
- Positive (correct)
- Imaginary
- Negative
- Zero
When a half-reaction is reversed, what effect does this have on the voltage (E)?
When a half-reaction is reversed, what effect does this have on the voltage (E)?
In balancing redox reactions, why is it important to balance the number of electrons transferred in each half-reaction?
In balancing redox reactions, why is it important to balance the number of electrons transferred in each half-reaction?
Consider the following balanced redox reaction: $2Al(s) + 3Cu^{2+}(aq) \rightarrow 2Al^{3+}(aq) + 3Cu(s)$. If the standard reduction potential for $Cu^{2+}$ is +0.34 V and for $Al^{3+}$ is -1.66 V, what is the overall voltage (E°) for this reaction?
Consider the following balanced redox reaction: $2Al(s) + 3Cu^{2+}(aq) \rightarrow 2Al^{3+}(aq) + 3Cu(s)$. If the standard reduction potential for $Cu^{2+}$ is +0.34 V and for $Al^{3+}$ is -1.66 V, what is the overall voltage (E°) for this reaction?
In an electrolytic cell, if a metal is being plated onto a cathode, what change in mass will be observed at the anode?
In an electrolytic cell, if a metal is being plated onto a cathode, what change in mass will be observed at the anode?
What does ΔG represent in the equation ΔG = -nFE?
What does ΔG represent in the equation ΔG = -nFE?
If a current of 5.0 amps is applied for 300 seconds, what is the total charge (Q) in coulombs that has flowed?
If a current of 5.0 amps is applied for 300 seconds, what is the total charge (Q) in coulombs that has flowed?
In the electrolysis of a solution of $CuSO_4$, a current is passed resulting in the deposition of copper metal. If it is known that 2 moles of electrons are required to deposit 1 mole of copper, how many grams of copper will be deposited by 96,500 coulombs of charge?
In the electrolysis of a solution of $CuSO_4$, a current is passed resulting in the deposition of copper metal. If it is known that 2 moles of electrons are required to deposit 1 mole of copper, how many grams of copper will be deposited by 96,500 coulombs of charge?
A standard reduction potential chart lists half-reactions as both gaining and losing electrons.
A standard reduction potential chart lists half-reactions as both gaining and losing electrons.
A negative overall standard cell potential (E) indicates a spontaneous reaction.
A negative overall standard cell potential (E) indicates a spontaneous reaction.
To obtain a positive overall standard cell potential (E) from two half-reactions, the half-reaction with a positive voltage needs to be flipped.
To obtain a positive overall standard cell potential (E) from two half-reactions, the half-reaction with a positive voltage needs to be flipped.
Flipping a half-reaction converts the process from reduction to oxidation, and the sign of its voltage remains unchanged.
Flipping a half-reaction converts the process from reduction to oxidation, and the sign of its voltage remains unchanged.
When balancing half-reactions, multiplying the coefficients affects the voltage (E) of the half-reaction.
When balancing half-reactions, multiplying the coefficients affects the voltage (E) of the half-reaction.
If the half reactions are balanced, the overall voltage of a cell can be found by multiplying the voltage of each half-reaction.
If the half reactions are balanced, the overall voltage of a cell can be found by multiplying the voltage of each half-reaction.
In the zinc-silver reaction, zinc goes from aqueous to solid, resulting in a loss of mass of the silver electrode.
In the zinc-silver reaction, zinc goes from aqueous to solid, resulting in a loss of mass of the silver electrode.
The equation $\Delta G = -nFE$ relates Gibbs free energy ($\Delta G$) to the number of protons transferred (n), Faraday's constant (F), and standard cell potential (E).
The equation $\Delta G = -nFE$ relates Gibbs free energy ($\Delta G$) to the number of protons transferred (n), Faraday's constant (F), and standard cell potential (E).
Faraday's constant (F) is equal to 96,500 Coulombs per mole of protons.
Faraday's constant (F) is equal to 96,500 Coulombs per mole of protons.
Producing 120 amps of current for 60 seconds requires approximately 23.5 grams of zinc.
Producing 120 amps of current for 60 seconds requires approximately 23.5 grams of zinc.
Flashcards
Standard Cell Potential (E°)
Standard Cell Potential (E°)
Voltage measured under standard conditions (25°C).
Standard Reduction Potential Chart
Standard Reduction Potential Chart
Lists half-reactions as reduction processes (gain of electrons).
Positive Overall E°
Positive Overall E°
Indicates a spontaneous reaction will occur.
Flipping a Half-Reaction
Flipping a Half-Reaction
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Balancing Electrons in Half-Reactions
Balancing Electrons in Half-Reactions
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Combining Half-Reactions
Combining Half-Reactions
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Electrom Thermo Equation
Electrom Thermo Equation
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Electrochemistry & Stoichiometry Equation
Electrochemistry & Stoichiometry Equation
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Converting Charge to Moles of Electrons
Converting Charge to Moles of Electrons
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Calculating Mass of Metal
Calculating Mass of Metal
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Oxidation Reaction
Oxidation Reaction
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Reduction Reaction
Reduction Reaction
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Multiplying Coefficients
Multiplying Coefficients
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Faraday's Constant (F)
Faraday's Constant (F)
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Negative Overall E
Negative Overall E
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Study Notes
Standard Cell Potential Calculation
- Standard conditions are at 25°C, denoted by the degree symbol (°).
- To calculate the standard cell potential (E), a standard reduction potential chart is needed.
- Standard reduction potential charts list half-reactions, all written as gaining electrons (reduction).
- To find the overall voltage, identify the half-reactions for the metals involved (e.g., zinc and silver) on the chart.
- For silver: Ag+ + e- → Ag, E = 0.8 volts
- For zinc: Zn+2 + 2e- → Zn, E = -0.76 volts
- A positive overall E indicates a spontaneous reaction; a negative E indicates a non-spontaneous reaction requiring electrolysis.
- If the overall E is negative, the reaction will need electrolysis, or electricity, to proceed because, being non-spontaneous, it needs energy to proceed.
Oxidation and Reduction
- The half-reaction with a negative voltage needs to be flipped to make the overall E positive.
- Flipping a reaction changes it from reduction to oxidation.
- The reaction that is flipped is the oxidation reaction
- When flipping a reaction, change the sign of its voltage (e.g., -0.76 volts becomes +0.76 volts).
Balancing Half-Reactions
- Balance the number of electrons in both half-reactions by multiplying coefficients as needed to achieve the same number of electrons.
- Multiplying coefficients does not change the voltage (E) of the half-reaction; voltage is independent of coefficients.
Calculating Overall Cell Potential
- Add the balanced half-reactions together, including reactants, products, and voltages.
- The overall voltage (standard cell potential) is the sum of the voltages of the half-reactions
- Example overall cell potential is 1.56 volts
- In the example reaction, zinc goes from solid to aqueous, and silver goes from aqueous to solid.
- In the example reaction, silver gains mass, and zinc loses mass.
- The number of electrons transferred in the balanced equation is noted for further calculations.
Electrochemical Equations
- ΔG = -nFE relates Gibbs free energy (ΔG) to the number of electrons transferred (n), Faraday's constant (F), and standard cell potential (E).
- F (Faraday's constant) = 96,500 Coulombs per mole of electrons.
- I = Q/T, where I is current in amperes, Q is charge in Coulombs, and T is time in seconds.
Stoichiometry Example
- Given current and time, calculate the charge (Q) in Coulombs.
- Use Faraday's constant to convert Coulombs to moles of electrons.
- Use the balanced reaction to find the ratio of moles of electrons to moles of substance (e.g., zinc).
- Convert moles of substance to grams using molar mass.
- Produced 120 amps of current in 60 seconds
- Producing 120 amps for 60 seconds requires approximately 2.35 grams of zinc.
- The gram amount corresponds to the amount of zinc needed to produce electricity at a given current and time.
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