Explain electromotive pressure. Construct the referral hydrogen electrode and explain why it is a reference. Distinguish reduction potentials from oxidation potentials. Calculate the typical potential from the reduction potentials.

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Electromotive Force (EMF)

The electromotive pressure (EMF) is the maximum potential distinction between 2 electrodes of a galvanic or voltaic cell. This amount is concerned the tendency for an aspect, a compound or an ion to obtain (i.e. gain) or release (lose) electrons. For instance, the maximum potential in between (ceZn) and also (ceCu) of a famous cell

(ce, Cu^2+: (1: M), )

has actually been measured to be 1.100 V. A concentration of 1 M in a suitable solution is defined as the conventional condition, and also 1.100 V is therefore the traditional electromotive force, DEo, or conventional cell potential for the (ceZn-Cu) galvanic cell.


The conventional cell potential, DEo, of a galvanic cell have the right to be evaluated from the conventional reduction potentials of the 2 fifty percent cells Eo. The reduction potentials are measured versus the typical hydrogen electrode (SHE):

(mathrm, H^+: (1.0: M)).

Its reduction potential or oxidation potential is characterized to be exactly zero.


The reduction potentials of all other half-cells measured in volts versus the SHE are the difference in electrical potential energy per coulomb of charge.

Note that the unit for energy J = Coulomb volt, and the Gibbs totally free energy G is the product of charge q and also potential difference E:

G in J = q E in C V

for electrical power calculations.

Example 1

What is the potential for the adhering to cell?

(mathrm, Zn^2+:(1.0: M), )


From a table of traditional reduction potentials we have the complying with values

(ceCu^2+ + 2 e^- ightarrow Cu hspace15px E^circ = 0.337 ag1)

(ceZn ightarrowhead Zn^2+ + 2 e^- hspace15px E^* = 0.763 ag2)

Add (1) and also (2) to yield

(ceZn + Cu^2+ ightarrow Zn^2+ + Cu hspace15px ce D E^circ = E^circ + E^* = extrm1.100 V)

Note that E* is the oxidation conventional potential, and also E° is the reduction typical potential, E* = - E°. The traditional cell potential is represented by dE°.

DISCUSSIONThe positive potential confirms your monitoring that zinc metal reacts via cupric ions in solution to produce copper steel.


The electromotive pressure (EMF) is the maximum potential distinction in between two electrodes of a galvanic or voltaic cell. The standard reduction potential of (M^ce n+,: 1: ce M ,|, M) couple is the standard cell potential of the galvanic cell:


The conventional oxidation potential of (M ,|, M^ce n+,: 1: ce M) couple is the typical cell potential of the galvanic cell:

(mathrm, H_2,: 1: atm, )

If the cell potential is negative, the reaction is reversed. In this situation, the electrode of the galvanic cell should be composed in a reversed order.


In which cell does reduction take place? The right-hand also cell or the left-hand also cell in the notation


Reduction potentials of half cells are measured against what? The zinc half cell (ce, Zn^2+: 1: M). The hydrogen fifty percent cell (cePt ,). The hydrogen fifty percent cell (ce, Pt). The copper half cell (ceCu^2+: 1: M ,). The hydrogen half cell (cePt ,). Is the potential for the battery

(ce, Cl- ,)

positive or negative?


Answer... Right Consider... Oxidation takes area in the left hand also cell. Reduction takes area in the best hand also cell or cathode. Answer... B. Consider...

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(ce, right)

offers the reduction potential. Answer... Confident Consider...

(eginalign ceCl2 + 2 e^- ightarrow 2 Cl- &hspace15pxE^circ = 1.36\ mathrmH_2 ightarrow 2 H^+ + 2 e^- &hspace15px E^circ = 0.00\ overlinehspace140px&overlinehspace100px\ ceCl2 + H2 ightarrowhead 2 HCl hspace15px &hspace15pxce DE^circ = 1.36: ce V endalign)