2. What is the reduction half-reaction for the following unbalanced redox equation?

Cr2O72– + NH4+ Cr2O3 + N2

A.) Cr2O3 -> Cr2O7^2–
*B.) Cr2O72– -> Cr2O3
C.) NH4+ -> N2
D.) N2 -> NH4+

3. Which oxidation-reduction reactions are best balanced by the half-reaction method?

A.) covalent reactions
B.) acid-base reactions
*C.) ionic reactions
D.) intermolecular reactions

Thank you.

Answered above.

2. The reduction half-reaction for the given unbalanced redox equation is: Cr2O72– -> Cr2O3.

3. The half-reaction method is best suited for balancing ionic reactions.

To find the reduction half-reaction for the given redox equation, you need to identify the element or compound that is undergoing reduction. In a reduction half-reaction, the oxidation state of an element or compound decreases.

In the given redox equation Cr2O72– + NH4+ Cr2O3 + N2, the chromium ion Cr2O72– is being reduced because its oxidation state decreases from +6 to +3 in the product Cr2O3.

Therefore, the correct reduction half-reaction for the given redox equation is:

Cr2O72– -> Cr2O3 (B)

To determine which oxidation-reduction reactions are best balanced by the half-reaction method, you need to consider the types of compounds involved.

The half-reaction method is most appropriate for balancing ionic reactions (C) because it allows you to focus on the oxidation and reduction processes separately. In these reactions, there are clear changes in oxidation states, making it easier to identify the electron transfer involved.

Covalent reactions (A) and acid-base reactions (B) do not typically involve clear changes in oxidation states, so they are not best balanced using the half-reaction method.

Intermolecular reactions (D) may involve a variety of reaction types, making it difficult to generalize whether the half-reaction method is best for balancing them.

Therefore, the correct answer is:

Ionic reactions (C) are best balanced by the half-reaction method.