Using standard reduction potentials (Appendix E), calculate the standard emf for each of the following reactions: (a) Cl21g2 + 2 I-1aq2 ¡ 2 Cl-1aq2 + I21s2

Verified step by step guidance

1. Identify the half-reactions involved in the overall reaction. For the given reaction, the half-reactions are: \( \text{Cl}_2(g) + 2e^- \rightarrow 2\text{Cl}^-(aq) \) and \( 2\text{I}^-(aq) \rightarrow \text{I}_2(s) + 2e^- \).
2. Look up the standard reduction potentials for each half-reaction in Appendix E. The standard reduction potential for \( \text{Cl}_2(g) + 2e^- \rightarrow 2\text{Cl}^-(aq) \) is typically positive, while for \( \text{I}_2(s) + 2e^- \rightarrow 2\text{I}^-(aq) \) it is less positive.
3. Reverse the oxidation half-reaction to match the direction of the given reaction. This means reversing \( 2\text{I}^-(aq) \rightarrow \text{I}_2(s) + 2e^- \) to \( \text{I}_2(s) + 2e^- \rightarrow 2\text{I}^-(aq) \) and changing the sign of its standard reduction potential.
4. Calculate the standard electromotive force (emf) of the reaction by adding the standard reduction potential of the reduction half-reaction (\( \text{Cl}_2(g) + 2e^- \rightarrow 2\text{Cl}^-(aq) \)) to the reversed oxidation potential (\( \text{I}_2(s) + 2e^- \rightarrow 2\text{I}^-(aq) \)).
5. The standard emf of the reaction is the sum of the potentials from step 4. This value indicates the tendency of the reaction to occur spontaneously under standard conditions.

Key Concepts

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) is the voltage generated by the cell when no current is flowing, representing the maximum potential difference between the two electrodes. The standard EMF can be calculated using the standard reduction potentials of the half-reactions involved.

Nernst Equation

The Nernst equation relates the cell potential to the concentrations of the reactants and products in a redox reaction. It allows for the calculation of the EMF under non-standard conditions, taking into account temperature and concentration changes. Understanding this equation is essential for accurately determining the cell potential in various scenarios.