Question

Consider the following reaction in a sealed container: $$ 2 \mathrm{NOBr}(g) \rightleftharpoons 2 \mathrm{NO}(g)+\mathrm{Br}_{2}(g) $$ Can you reach a state of equilibrium if you start with (a) just NOBr? (b) just \(\mathrm{Br}_{2}\) ? (c) just \(\mathrm{Br}_{2}\) and \(\mathrm{NOBr}\) ? (d) just \(\mathrm{NO}\) and \(\mathrm{Br}_{2}\) ?

Short answer

(a) Yes, an equilibrium can be reached starting with just NOBr. (b) No, an equilibrium cannot be reached when starting with just Br2. (c) Yes, an equilibrium can be reached starting with just Br2 and NOBr. (d) Yes, an equilibrium can be reached starting with just NO and Br2.

Step-by-step solution

Situation (a) - just NOBr

In this case only NOBr is present. Since this reaction is reversible, the NOBr will decompose into NO and Br2 until an equilibrium is reached where the decomposition of NOBr and the formation of NOBr from NO and Br2 happen at the same rate.

Situation (b) - just \(Br_{2}\)

In this case only Br2 is present. However, for the forward reaction to happen, NO (Nitrogen Oxide) is also required alongside Br2. Since NO is not present initially, the reaction cannot proceed in the reverse direction. Therefore, an equilibrium cannot be reached when starting with only Br2.

Situation (c) - just \(Br_{2}\) and NOBr

In this case, Br2 and NOBr are present. The NOBr can decompose into NO and Br2 while the NO can react with Br2 to form more NOBr. Therefore, an equilibrium state can be achieved as both forward and backward reactions can occur.

Situation (d) - just NO and \(Br_{2}\)

In this case, NO and Br2 are present. These can combine to form NOBr as per the reverse reaction. Simultaneously, the NOBr formed can decompose back into NO and Br2. Therefore, an equilibrium can be achieved in this scenario where both the forward and backward reactions can occur.

Key concepts

Reversible Reactions

Reversible reactions are a fascinating aspect of chemical processes. They occur when the products of a chemical reaction can react together to reform the initial reactants. This means that the reaction does not have a definite endpoint; instead, it can move back and forth under certain conditions.

In the context of the given reaction \(2 \text{NOBr}(g) \rightleftharpoons 2 \text{NO}(g) + \text{Br}_2(g)\), it is important to note that both the formation of products from reactants and the recombination of products back to reactants are possible.

• If a reaction is initiated starting with only NOBr, it will decompose into NO and Brerate-creating NOBr.
• If a reaction is set in motion with NO and Br2, they can combine to produce NOBr.This back-and-forth dynamic allows the reaction to potentially reach a state of equilibrium, where the rate of the forward reaction equals the rate of the reverse reaction.

Reaction Rates

Understanding reaction rates is crucial in determining how a system reaches equilibrium in reversible reactions. Reaction rates dictate how quickly reactants convert into products and vice versa. Two major factors that can influence these rates are the concentration of reactants and the presence of catalysts.

In situations (a) and (c) of our exercise, where NOBr is present, it can break down into NO and Br2. As the forward reaction progresses, the concentration of NO and Br2 increases, which in turn accelerates the reverse reaction rate, eventually leading to equilibrium. On the other hand, situation (b) highlights that without necessary reactants such as NO, the reaction cannot proceed, leaving no room for establishing equilibrium.

• Reaction rates are directly proportional to the concentration of reactants. This means more molecules present will lead to more frequent successful collisions, thus increasing the reaction rate. The equilibrium state is achieved when the rate of the forward reaction matches the rate of the reverse reaction.

Gaseous Reactions

Gaseous reactions, like the one illustrated in the exercise, involve reactants and products in their gaseous states. These reactions often happen in sealed containers, allowing for careful study and control over conditions like pressure and volume.

In the given exercise, gases such as NOBr, NO, and Br2 are involved. Gaseous states are unique due to their ability to spread and fill any available space, allowing for better interactions between reactant molecules.

• The ideal gas law \(PV=nRT\) often helps describe the behavior of gases under these conditions.In a closed system, such as a sealed container, no gases escape or enter, ensuring that all the reaction dynamics happen internally.Pressure can build up as reactions proceed, influencing not only the rate but also the position of equilibrium.Understanding gaseous reactions' dynamic nature is essential to grasp how shifts in equilibrium occur in various reaction scenarios.