Determine whether or not each redox reaction occurs spontaneously in the forward direction.
a. Ni(s) + Zn²⁺(aq) → Ni²⁺(aq) + Zn(s)
b. Ni(s) + Pb²⁺(aq) → Ni²⁺(aq) + Pb(s)
c. Al(s) + 3 Ag⁺(aq) → Al³⁺(aq) + 3 Ag(s)
d. Pb(s) + Mn²⁺(aq) → Pb²⁺(aq) + Mn(s)

Verified step by step guidance

1. Identify the oxidation and reduction half-reactions. In this case, Ni(s) is oxidized to Ni2+(aq) and Zn2+(aq) is reduced to Zn(s).
2. Write the half-reactions with their respective oxidation states. For Nickel: Ni(s) → Ni2+(aq) + 2e-, and for Zinc: Zn2+(aq) + 2e- → Zn(s).
3. Look up the standard reduction potentials for each half-reaction in a standard reduction potential table. The standard reduction potential for Ni2+/Ni is -0.25 V and for Zn2+/Zn is -0.76 V.
4. Calculate the standard cell potential (E°cell) for the reaction using the formula: E°cell = E°cathode - E°anode. Here, the cathode is the reduction half-reaction (Zn2+ to Zn) and the anode is the oxidation half-reaction (Ni to Ni2+).
5. Determine the spontaneity of the reaction. If E°cell is positive, the reaction is spontaneous in the forward direction. If E°cell is negative, the reaction is non-spontaneous in the forward direction.

Key Concepts

Redox Reactions

Redox reactions, or reduction-oxidation reactions, involve the transfer of electrons between two species. In these reactions, one species is oxidized (loses electrons) while the other is reduced (gains electrons). Understanding the oxidation states and identifying the oxidizing and reducing agents are crucial for analyzing these reactions.

Standard Electrode Potentials

Standard electrode potentials (E°) are measured values that indicate the tendency of a species to be reduced. Each half-reaction has a specific E° value, and the overall cell potential can be calculated by subtracting the reduction potential of the anode from that of the cathode. A positive cell potential indicates that the reaction is spontaneous in the forward direction.

Spontaneity of Reactions

A reaction is considered spontaneous if it occurs without external intervention, which is often determined by the Gibbs free energy change (ΔG). For redox reactions, if the cell potential (E°) is positive, the reaction will have a negative ΔG, indicating that it is spontaneous. Conversely, a negative cell potential suggests that the reaction is non-spontaneous in the forward direction.