Question

How do you identify reducing agents, oxidizing agents, or whether neither of these two apply?

for example:
`N_2 + 3H_2 -> 2NH_3`
`2N_2 + O_2 -> 2N_2O`

Answer 1

Reducing agents are the element(s) that are oxidized (oxidation state increases) and oxidizing agents are the element(s) that are reduced oxidation state decreases).

Explanation:

You MUST have BOTH for a redox reaction to occur! So, look for the two (or more) elements in an equation whose reaction change requires a CHANGE in their oxidation state. If no change is found, the reaction is not a redox reaction (there are many more types).

In your examples,
a) Nitrogen is being reduced from an oxidation state of 0 to -3, so it is the oxidizing agent. Hydrogen is being oxidized from an oxidation state of 0 to +1, so it is the reducing agent.
b) Nitrogen is being oxidized from an oxidation state of 0 to +1, so it is the reducing agent. Oxygen is being reduced from an oxidation state of 0 to -2, so it is the oxidizing agent.