One of the components of polluted air is NO. It is formed in the high- temperature environment of internal combustion engines by the following reaction: $$ \mathrm{N}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{NO}(g) \quad \Delta H=180 \mathrm{kJ} $$ Why are high temperatures needed to convert \(\mathrm{N}_{2}\) and \(\mathrm{O}_{2}\) to NO?

First, let us analyze the given reaction: \[ \text{N}_2(g) + \text{O}_2(g) \rightarrow 2 \text{NO}(g) \quad \Delta H = 180 \text{ kJ} \] This reaction represents the formation of nitrogen monoxide (NO) from nitrogen (N2) and oxygen (O2) molecules. Notice that the reaction is endothermic, as indicated by the positive enthalpy change (\(\Delta H = 180 \text{ kJ}\)). This means that the reaction requires energy to proceed.

Now let's focus on the bond strengths and dissociation energies involved in this reaction. Both N2 and O2 molecules have very strong bonds, with triple bonds in N2 (\(\text{N} \equiv \text{N}\)) and double bonds in O2 (\(\text{O} = \text{O}\)). These strong bonds result in high bond dissociation energies, meaning that a significant amount of energy is required to break these bonds. The energy needed to break one mole of N2 triple bonds is approximately 945 kJ/mol, while the energy needed to break one mole of O2 double bonds is around 498 kJ/mol. On the other hand, the bond dissociation energy for NO is around 631 kJ/mol. This means that the energy required to break the N2 and O2 bonds is greater than the energy released when forming NO bonds.

Since the reaction is endothermic and high bond dissociation energies are involved, a large amount of energy must be provided to overcome the energy barrier for the reaction to proceed. By providing a high-temperature environment, the necessary energy is supplied to break the N2 and O2 bonds and allow the formation of NO molecules. The high temperature provides the kinetic energy needed by the reactant molecules to collide with sufficient energy to overcome the activation energy required for the reaction to proceed.

In conclusion, high temperatures are required to convert N2 and O2 into NO because the reaction is endothermic, and strong bonds in the N2 and O2 molecules need to be broken for the reaction to occur. The high-temperature environment supplies the necessary energy to overcome the energy barrier, allowing the strong N2 and O2 bonds to be broken and the formation of NO molecules to take place.