Question

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?

Short answer

High temperatures are needed to convert \(\mathrm{N}_{2}\) and \(\mathrm{O}_{2}\) to NO because the reaction is endothermic, requiring a large amount of energy to overcome the activation energy barrier and break the strong bonds in the reactants. Higher temperatures also increase the probability of more frequent and energetic collisions between reactant molecules, thus facilitating the formation of the activated complex leading to the production of NO.

Step-by-step solution

Understand the reaction

The given reaction is a synthesis reaction between nitrogen gas (\(\mathrm{N}_{2}\)) and oxygen gas (\(\mathrm{O}_{2}\)) to produce nitric oxide (NO). The reaction can be represented as: \[\mathrm{N}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{NO}(g)\] The energy change for this reaction is provided: \(\Delta H=180 \mathrm{kJ}\), which means this is an endothermic reaction, as it requires an input of energy to take place.

Understand activation energy

Activation energy, according to the collision theory of chemical reactions, is the minimum energy required for reactant molecules to collide and form an activated complex, which then leads to the formation of products. In an endothermic reaction, it requires more energy for the activation energy to be reached, as compared to an exothermic reaction. In such a case, the higher the temperature, the more reactant molecules will possess the required activation energy for the reaction to occur.

Discuss the role of high-temperature in the reaction

High temperatures are needed to convert \(\mathrm{N}_{2}\) and \(\mathrm{O}_{2}\) to NO for the following reasons: 1. High temperatures provide the necessary energy for the reaction to proceed, since it is an endothermic reaction. Higher temperatures cause a rise in the average kinetic energy of the molecules, increasing the likelihood that they possess sufficient energy to overcome the activation energy barrier. 2. Both \(\mathrm{N}_{2}\) and \(\mathrm{O}_{2}\) molecules have strong triple and double bonds, respectively. These bonds require a large amount of energy to be broken, which can be supplied by high temperatures. 3. Higher temperatures lead to more frequent and energetic collisions between reactant molecules, increasing the probability of the formation of the activated complex that eventually forms NO. As a result, the reaction rate is faster at higher temperatures. In conclusion, high temperatures are needed to convert \(\mathrm{N}_{2}\) and \(\mathrm{O}_{2}\) to NO because the reaction is endothermic and requires a substantial amount of energy to break the strong bonds in the reactants and facilitate the formation of the activated complex, which eventually results in the formation of NO.

Key concepts

Activation Energy

Activation energy is a core concept in understanding why certain reactions need a particular amount of energy to get started. Imagine trying to push a ball over a hill. The hill represents the activation energy. Until enough energy is applied to push the ball over, it will remain stuck.

In the context of chemical reactions, activation energy is the minimum energy necessary for molecules to collide in such a way that a reaction can occur. This energy allows the reactants to form an "activated complex," a temporary state before the final products are formed.

In endothermic reactions, like the formation of NO from \(_2\) and \( ext{O}_2\), a significant input of energy is crucial. Higher activation energy means that more energy is required initially for the reaction molecules to reach this activated state. In other words, the reaction's mountain is steeper, requiring that significant energy input to push reactants over the barrier so the products can be formed. Therefore, without enough activation energy, the reactants will not transform into products.

High Temperature Reactions

High temperatures play a vital role in initiating and sustaining reactions that require intense energy input. When temperature increases, the molecules involved in a reaction move faster due to increased kinetic energy. This greater speed enhances the frequency and energy of collisions—key components in overcoming activation energy barriers.

For the production of NO from \(_2\) and \( ext{O}_2\), high temperatures are essential. It's a bit like heating a pot of water to speed up boiling; more energy is introduced to the system, enabling a quicker reaction. In the case of NO formation, increasing temperature means that more molecules have enough energy to reach the activation threshold at any moment.

This increased energetic activity not only overcomes initial energetic barriers but also ensures a higher rate of successful collisions among molecules. Thus, high temperatures are indispensable in reactions with demanding energy needs, ensuring that enough reactant molecules can transform into products like NO.

Chemical Bond Breaking

The process of chemical bond breaking is integral to reactions like the formation of NO. Chemical bonds hold atoms together, and these bonds must be broken before the atoms can be rearranged into new products. Breaking bonds requires energy, often quite a bit, especially when involving strong bonds.

In reactions such as \(_2 + ext{O}_2 ightarrow 2 ext{NO}\), we are dealing with very stable molecules. \( ext{N}_2\) features a triple bond, and \( ext{O}_2\) contains a double bond. These are some of the strongest common bonds in chemistry, which means more energy (often from high temperatures) is needed to break them compared to weaker single bonds.

The amount of energy required to disrupt these bonds contributes to the overall energy demand of the reaction. This energy input must overcome the resistance of strong bonds before new bonds—such as those in NO—can form. Therefore, understanding the endothermic nature of this reaction and its reliance on thermal energy helps in grasping why bond breaking is so energy-intensive.