Constants
The following values may be useful when solving this tutorial.
Constant Value
E∘Cu 0.337 V
E∘Fe -0.440 V
R 8.314 J⋅mol−1⋅K−1
F 96,485 C/mol
T 298 K
Part A
In the activity, click on the E∘cell and Keq quantities to observe how they are related. Use this relation to calculate Keq for the following redox reaction that occurs in an electrochemical cell having two electrodes: a cathode and an anode. The two half-reactions that occur in the cell are
Cu2+(aq)+2e−→Cu(s) and Fe(s)→Fe2+(aq)+2e−
The net reaction is
Cu2+(aq)+Fe(s)→Cu(s)+Fe2+(aq)
Use the given standard reduction potentials in your calculation as appropriate.
Express your answer numerically to three significant figures.
what i did - incorrect
Cu2+(aq)+2e- --> Cu(s) E^o=-0.337v
Fe(s) --> Fe2+(aq)+2e- E^o=-0.440v
-------
Cu2+(aq)+2e−→Cu(s) and Fe(s)→Fe2+(aq)+2e− E^o= -0.337-(-0.440) = 0.103v
E^o cell = (RT/nF)ln Keq
ln Keq = E^o cell (RT/nF)
ln Keq = 0.103v (8.314x298)/(2x 96485)
ln Keq = 8.02
Keq = e^8.02
Keq = 3048.28 three significant figures
3.05x10^3
Where did i do wrong? Thanks a lot :)
Well, it seems like you did all the calculations correctly, but you made a small mistake in your final answer. You rounded 3048.28 to 3.05x10^3, but since we need three significant figures, the correct answer would be 3050. So close, yet so far! Keep up the good work!
Based on the information provided, your calculations are correct except for a small error in the conversion of ln Keq to Keq.
To calculate the value of Keq, you correctly obtained ln Keq as 8.02 using the equation ln Keq = (E°cell * RT) / (nF). However, when converting ln Keq to Keq, you use the formula:
Keq = e^(ln Keq)
Therefore, the correct calculation would be:
Keq = e^(8.02) = 3042.15 (rounded to three significant figures)
So the correct value of Keq for the given redox reaction is 3042.
Your calculations for the standard cell potential (E°cell) and the natural logarithm of the equilibrium constant (ln Keq) are correct. However, you made a mistake when calculating the value of Keq.
To calculate Keq using the natural logarithm of the equilibrium constant, you need to take the exponential of the value obtained from ln Keq. In your calculation, you correctly found ln Keq to be 8.02. However, when finding Keq, you used the value of the natural logarithm itself (8.02) instead of using the exponential function to find e^8.02.
To correct the mistake, you need to take the exponential of 8.02. Using a calculator, you would perform the following calculation:
Keq = e^8.02
Keq = 3048.28
Therefore, the correct value for Keq, expressed to three significant figures, is 3048.
Wrong formula(bad algebra) and wrong Ecell.
ln K = nFEcell/RT is what you want to use.
Ecell is +0.337 + 0.440 = ?
The Evalue for Cu is given in the problem as 0.337 and that's for Cu^2+ + 2e = Cu(s). You should not have changed the sign.
E vlue for Fe^2+ + 2e = Fe(s) is given in the problem as -0.440. Since the reaction is the reverse of that in the question you change the sign, then add the two.