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Stoichiometry is a vital concept in chemistry, dealing with the quantitative relationships between reactants and products in a chemical reaction. In our example, the stoichiometry of the reaction between nitrogen monoxide (NO) and bromine (\(\mathrm{Br}_{2}\)) to form nitrosyl bromide (\(\mathrm{NOBr}\)) is given by the balanced reaction equation:\[ 2 \mathrm{NO}(g) + \mathrm{Br}_{2}(g) \rightarrow 2 \mathrm{NOBr}(g) \]This equation tells us that two moles of NO react with one mole of \(\mathrm{Br}_{2}\) to produce two moles of \(\mathrm{NOBr}\). It's important to understand that coefficients in a balanced equation reveal the proportion in which substances react. These proportions are essential for predicting the amount of reactants required or products formed during a reaction. Stoichiometry allows us to establish these relationships, helping in calculating the moles of reactants and products at any stage of a chemical reaction.

The equilibrium composition describes the concentration of reactants and products when a chemical reaction reaches equilibrium. In an equilibrium state, the rate of the forward reaction equals the rate of the reverse reaction, and the amounts of all substances remain constant.In our chemical reaction example:- Initially, we start with 0.0524 moles of NO and 0.0262 moles of \(\mathrm{Br}_{2}\).- When the reaction reaches equilibrium, it forms 0.0311 moles of \(\mathrm{NOBr}\).Using stoichiometry, we can determine that:- 0.0311 moles of NO are consumed.- Consequently, 0.01555 moles of \(\mathrm{Br}_{2}\) are also consumed.The equilibrium composition of the mixture can be calculated by subtracting the reacted moles from the initial amounts for the reactants and adding the formed product moles:- NO at equilibrium: 0.0213 moles - \(\mathrm{Br}_{2}\) at equilibrium: 0.01065 moles- \(\mathrm{NOBr}\) at equilibrium: 0.0311 molesThis gives a snapshot of the mixture when the reaction ceases to change visibly.

Calculating moles is an essential skill in analyzing chemical reactions, especially when determining the quantities at different stages.To calculate the moles at equilibrium for our example, follow these steps:1. **Initial Moles**: Start with the known initial moles. Here, NO is 0.0524 mol and \(\mathrm{Br}_{2}\) is 0.0262 mol. Initially, \(\mathrm{NOBr}\) is nonexistent before the reaction progresses.2. **Change in Moles**: Using stoichiometry, we figure out the change in moles as the reaction proceeds. For instance, the production of 0.0311 moles of \(\mathrm{NOBr}\) implies a 0.0311 mol decrease in NO, and half of that, or 0.01555 mol decrease, in \(\mathrm{Br}_{2}\).3. **Equilibrium Moles**: Calculate the moles at equilibrium by adjusting the initial moles by the change: - NO becomes \(0.0524 - 0.0311 = 0.0213\) moles. - \(\mathrm{Br}_{2}\) becomes \(0.0262 - 0.01555 = 0.01065\) moles. - \(\mathrm{NOBr}\) stands at 0.0311 moles since it started from zero.This approach allows for clear and systematic determination of the equilibrium composition of a chemical reaction, essential for both academic and practical chemistry applications.