Question

Balance the following oxidation and reduction half-reactions for the decomposition of water.

__H2O → ___O2 + ___ H+ + ___4 e-
___H2O + ___e- →___ H2 + ____OH- a) 2, 2, 4, 4
b) 2, 1, 2, 2
c) 2, 4, 4, 2
d) 2, 2, 2, 4

Answer 1

The balanced half-reactions for the decomposition of water are 2 H₂O → O₂ + 4 H+ + 4 e- (oxidation) and 2 H₂O + 2 e- → H₂ + 2 OH- (reduction), which corresponds to the choice (a) 2, 1, 2, 2.

Step-by-step explanation:

To balance the given oxidation and reduction half-reactions for the decomposition of water, follow these steps:

1. Write the skeletal equations for oxidation and reduction half-reactions.
2. Balance all elements except oxygen (O) and hydrogen (H).
3. Balance oxygen atoms by adding H₂O molecules.
4. Balance hydrogen atoms by adding H+ ions.
5. Balance charge by adding electrons.
6. If necessary, multiply each half-reaction's coefficients by the smallest possible integers to yield equal numbers of electrons in each.

The balanced half-reactions for the decomposition of water are:

• Oxidation: 2 H₂O(l) → O₂(g) + 4 H+(aq) + 4 e-
• Reduction: 2 H₂O(l) + 2 e- → H₂(g) + 2 OH-(aq)

This corresponds to the choice (a) 2, 1, 2, 2 when balancing the given half-reactions.