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Electrochemistry Additional Practice

Related Topics

Wize University Chemistry Textbook > Electrochemistry

Important Equations + Nonstandard conditions (Nernst Equation)

6 Activities

checklist
Mark Yourself Question
  1. Grab a piece of paper and try this problem yourself.
  2. When you're done, check the "I have answered this question" box below.
  3. View the solution and report whether you got it right or wrong.

At 25C, what is the potential of the following cell and what is the Keq?

Ni|Ni2+(aq)(0.010 M)||Cr-(0.20 M)|Cr2(g) | Pt


1) Is the reaction occuring in standard or non-standard conditions?

If it is occuring in standard conditions --> it is asking us to solve for Eocell
If it is occuring in nonstandard conditions --> it is asking us to solve for Ecell


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2) Which equation will we use to solve this problem?

Nernst equation for non-standard conditions!
E = Eo - (RT/nF)ln(Q)

E is what the question is asking us to solve
Eo we can calculate by using the SRP from a table
R=8.314J/molK
n=# of electrons involved in the overall reaction
F=faraday's constant (96500C/mole-)
Q=[products]/[reactants]

3) Solve for Eocell using SRP tables:

Ni2+(aq) + 2e- --> Ni(s) Eo=-0.25 V
Cr2(g) + 2e- --> 2Cr-(aq) Eo=+1.36 V

From this the standard cell reaction would be:
Cr2(g) + 2e- --> 2Cr-(aq)
Eo=
Ni(s) --> Ni2+(aq) + 2e-
Eo=
to give Cr2(g) + Ni(s) --> 2Cr-(aq) + Ni2+(aq)
Eo=
1.61V

4) Now we can determine E at non-standard conditions via the NERNST Equation:

E = Eo - (RT/nF)ln(Q)

Bonus: Is this reaction spontaneous or not?

5) What is Keq at 298 K?

Keq = enFEo/RT
More Important Equations + Nonstandard conditions (Nernst Equation) Questions:
A comproportionation reaction is a reaction where one element in two different oxidation states reacts to form a product where both atoms now have the same oxidation state. An electrochemical cell can be constructed using the comproportionation of cobalt as shown below.
CO3++CO+→2CO2+CO^{3+}+CO^+ \to 2CO^{2+}
If the equilibrium constant for the above reaction is found to be 6.3 x 104 determine the standard cell potential ε0 and draw the electrochemical cell in standard notation
The E° for the reaction of Cu/Cu2+ and Sn/Sn2+ is + 0.19 V. What is the value of the equilibrium constant K for this reaction at 298 K?
Calculate the standard voltage and write the standard cell notation for a galvanic cell composed of the following two half reactions.
Fe2+ + 2e- --> Fe(s) Eo=-0.41V
Cr2O72- + 14H+ + 6e- → 2Cr3+ + 7H2O Eo=1.33V
Electrochemistry: Galvanic cells
For each galvanic cell, what is the value of the equilibrium constant for the reaction between each pair at 25 °C? Please ensure that your answer is specified to two decimal places and that your answer is formatted as follows: 9.15x1025 for both answers.
Ni(s) and Ag+(aq)
Fe(s) and Cr3+(aq)
If you could increase the concentration of Cu2+, which of the following would be true about the cell potential?
You make a cell with a copper electrode in a solution of copper nitrate and a silver electrode in a solution of silver nitrate.
Cu(s)+2Ag+(aq)⇌Cu2+(aq)+2Ag(s)      E=0.46VCu(s)+2Ag^+(aq)⇌Cu^{2+}(aq)+2Ag(s)\ \ \ \ \ \ E = 0.46 V
If you could increase the concentration of Ag+ , which of the following would be true about the cell potential?
Gibbs Free Energy and Voltage Practice Problem #1
What is the equilibrium constant for the reaction of copper metal with bromine to form copper(II) ions and bromide ions in aqueous solution at 25oC?
Cu(aq)2++2e−→Cu(s)Eo=+0.34 VBr2(aq)+2e−→2 Br(aq)−Eo=+1.07 V\begin{array}{cc} Cu^{2+}_{(aq)}+2e^- \rightarrow Cu_{(s)} & E^o=+0.34\ V\\ Br_{2(aq)}+2e^- \rightarrow 2\ Br^-_{(aq)} & E^o=+1.07\ V \end{array}