CHEM 120 Lecture Notes - Lecture 26: Standard Hydrogen Electrode, Standard Electrode Potential, Membrane Potential

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Standard cell potential is the difference in electrical potential between 2 electrodes, or the energy available to do the work of moving a charge between two electrodes. It is measured at 298 k with no current flowing & all components in standard states. Si unit: volt (v) = energy (joule) released per charge (coulomb) (1v = 1j/c) E cell = e cathode - e anode: the substraction takes into account the fact that all e halfcell values reported for reverse reaction (reduction) Standard electrode potential, (e halfcell) is the potential of a given half-reaction relative to standard hydrogen electrode. The stronger the oxidizing agent/weaker the reducing agent, the more easily the electrons are accepted and the forward reaction is favored (e halfcell is +ve) The stronger the reducing agent/weaker the oxidizing agent, the more easily it loses electrons, and so the reverse reaction is favored (e halfcell is ve)

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Consider the following table of standard reduction potentials.

Half-reaction	E ^o (V)
Cu²⁺(aq) + 2e^? ? Cu(s)	+0.34
Pb²⁺(aq) + 2e^? ? Pb(s)	-0.126
Cd²⁺(aq) + 2e^? ? Cd(s)	-0.403
Zn²⁺(aq) + 2e^? ? Zn(s)	-0.76

Based on these values, which of the following choices represents the correct combination of cell reaction and standard cell potential?

	Cu²⁺(aq) + Cd(s) ? Cu(s) + Cd²⁺(aq), +0.06 V
	Cu²⁺(aq) + Zn(s) ? Cu(s) + Zn²⁺(aq), ?0.42 V
	Pb²⁺(aq) + Cd(s) ? Pb(s) + Cd²⁺(aq), +0.53 V
	Pb²⁺(aq) + Zn(s) ? Pb(s) + Zn²⁺(aq), +0.63 V

Constant	Value
Ecu	0.337
Ezn	-7.63
R	8.314
F	96,485
T	298

In the activity, click on the Eâcell 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)+2eââCu(s) and Zn(s)âZn2+(aq)+2eâ

The net reaction is

Cu2+(aq)+Zn(s)âCu(s)+Zn2+(aq)

Use the given standard reduction potentials in your calculation as appropriate.

1. Consider a voltaic (galvanic) cell with the following metal electrodes. Identify which metal is the cathode and which is the anode, and calculate the cell potential.

(a) Al and Co(II)
Cathode: ____

Anode: ______

Ecell =

(b) Cd(II) and Ag(I)

cathode: ___

anode: ___

Ecell= ____

cathode: ___

Anode:_____

Ecell:____

2. A voltaic cell contains two half-cells. One half-cell contains a titanium electrode immersed in a 1.00 M Ti(NO₃)₃ solution. The second half-cell contains a zinc electrode immersed in a 1.00 M Zn(NO₃)₂ solution.

Ti³⁺(aq) + 3 e^â â Ti(s)	Eâ°redâ = â1.370 V
Zn²⁺(aq) + 2 e^â â Zn(s)	Eâ°redâ = â0.762 V

(a) Using the standard reduction potentials given above, predict the standard cell potential of the voltaic cell.

(b) Write the overall balanced equation for the voltaic cell. (Include states-of-matter under the given conditions in your answer.)

3. ÎGÂ° and EÂ° can be said to measure the same thing, and are convertible by the equation

ÎGÂ° = ânFEâ°cellâ

where n is the total number of moles of electrons being transferred, and F is the Faraday constant 9.64853415âââ10⁴ C/mol. The free energy (ÎGÂ°) of a spontaneous reaction is always negative.

For each of the electrochemical cells below, calculate the free energy of the system and state whether the reaction is spontaneous or non-spontaneous as written based on the cathode and anode assignment given. (Use the table of Standard Electrode Potentials.)

(a) The cathode is Zn(II) and the anode is Co(II).

free energy: ____ kJ

spontaneity: _____

CHEM 120 Lecture Notes - Lecture 26: Standard Hydrogen Electrode, Standard Electrode Potential, Membrane Potential

CHEM 120 Full Course Notes

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