The commercial production of nitric acid involves the following chemical reactions: $$ \begin{aligned} 4 \mathrm{NH}_{3}(g)+5 \mathrm{O}_{2}(g) & \longrightarrow 4 \mathrm{NO}(g)+6 \mathrm{H}_{2} \mathrm{O}(g) \\ 2 \mathrm{NO}(g)+\mathrm{O}_{2}(g) & \longrightarrow 2 \mathrm{NO}_{2}(g) \\ 3 \mathrm{NO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(l) & \longrightarrow 2 \mathrm{HNO}_{3}(a q)+\mathrm{NO}(g) \end{aligned} $$ (a) Which of these reactions are redox reactions? (b) In each redox reaction identify the element undergoing oxidation and the element undergoing reduction.

First, let's assign oxidation numbers to each element in each reaction. Reaction 1: \(4 \,\text{NH}_3(g) + 5 \,\text{O}_2(g) \longrightarrow 4\, \text{NO}(g) + 6 \,\text{H}_2\text{O}(g)\) \(N: -3, +2; H: +1; O: 0, -2\) Reaction 2: \(2\, \text{NO}(g) + \text{O}_2(g) \longrightarrow 2\, \text{NO}_2(g)\) \(N: +2, +4; O: 0, -2\) Reaction 3: \(3 \,\text{NO}_2(g) + \text{H}_2\text{O}(l) \longrightarrow 2 \,\text{HNO}_3(aq) + \text{NO}(g)\) \(N: +4, +5, +2; H: +1; O: -2\)

Now that we have assigned oxidation numbers, let's find out which of these reactions are redox reactions by looking for changes in oxidation numbers. Reaction 1: \(N\) changes from -3 to +2 (oxidation), and \(O\) changes from 0 to -2 (reduction). So, Reaction 1 is a redox reaction. Reaction 2: \(N\) changes from +2 to +4 (oxidation), and \(O\) changes from 0 to -2 (reduction). So, Reaction 2 is also a redox reaction. Reaction 3: \(N\) changes from +4 to +5 and +2 (both oxidation and reduction). So, Reaction 3 is a redox reaction as well. (a) All three reactions are redox reactions.

Let's now identify the elements undergoing oxidation and reduction in each redox reaction. Reaction 1: Oxidation: \(N\) in NH3, as oxidation number increases from -3 to +2. Reduction: \(O\) in O2, as oxidation number decreases from 0 to -2. Reaction 2: Oxidation: \(N\) in NO, as oxidation number increases from +2 to +4. Reduction: \(O\) in O2, as oxidation number decreases from 0 to -2. Reaction 3: Oxidation: \(N\) in NO2, as oxidation number increases from +4 to +5 (in HNO3) Reduction: \(N\) in NO2, as oxidation number decreases from +4 to +2 (in NO) (b) In Reaction 1, \(N\) is oxidized and \(O\) is reduced. In Reaction 2, \(N\) is oxidized and \(O\) is reduced, and in Reaction 3, \(N\) undergoes both oxidation and reduction.