Using standard reduction potentials (Appendix E), calculate the standard emf for each of the following reactions: (b) Ni1s2 + 2 Ce4+1aq2 ¡ Ni2+1aq2 + 2 Ce3+1aq2

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Identify the half-reactions involved in the overall redox reaction. For the given reaction, the half-reactions are: \( \text{Ni} \rightarrow \text{Ni}^{2+} + 2e^- \) and \( \text{Ce}^{4+} + e^- \rightarrow \text{Ce}^{3+} \).

Look up the standard reduction potentials for each half-reaction in Appendix E. The standard reduction potential for \( \text{Ni}^{2+} + 2e^- \rightarrow \text{Ni} \) is \( E^\circ = -0.25 \text{ V} \), and for \( \text{Ce}^{4+} + e^- \rightarrow \text{Ce}^{3+} \) is \( E^\circ = +1.61 \text{ V} \).

Reverse the reduction potential for the oxidation half-reaction. Since \( \text{Ni} \rightarrow \text{Ni}^{2+} + 2e^- \) is the oxidation half-reaction, its potential becomes \( E^\circ = +0.25 \text{ V} \).

Calculate the standard emf (electromotive force) of the cell by adding the standard potentials of the oxidation and reduction half-reactions: \( E^\circ_{\text{cell}} = E^\circ_{\text{reduction}} + E^\circ_{\text{oxidation}} \).

Substitute the values into the equation: \( E^\circ_{\text{cell}} = 1.61 \text{ V} + 0.25 \text{ V} \).

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Standard Reduction Potentials

Standard reduction potentials are measured voltages that indicate the tendency of a chemical species to gain electrons and be reduced. Each half-reaction has a specific potential, typically measured under standard conditions (1 M concentration, 1 atm pressure, and 25°C). These values are crucial for predicting the direction of redox reactions and calculating the overall cell potential.

Electrochemical Cell and EMF

An electrochemical cell consists of two half-cells where oxidation and reduction reactions occur. The electromotive force (EMF) of the cell is the voltage generated by the spontaneous redox reaction, calculated as the difference between the reduction potentials of the cathode and anode. A positive EMF indicates a spontaneous reaction, while a negative EMF suggests non-spontaneity.

Balancing Redox Reactions

Balancing redox reactions involves ensuring that both mass and charge are conserved in the reaction. This is done by identifying oxidation and reduction half-reactions, balancing the number of electrons transferred, and adjusting coefficients accordingly. Properly balanced reactions are essential for accurate calculations of standard EMF and understanding the stoichiometry of the reaction.