Consider the reaction: H2(g) + Br2(g) → 2 HBr(g). The graph shows the concentration of Br2 as a function of time. a. Use the graph to calculate each quantity: (ii) the instantaneous rate of the reaction at 25 s.

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Identify the concentration of Br₂ at times just before and just after 25 seconds from the graph to estimate the change in concentration around that point.

Calculate the change in concentration of Br₂ (Δ[Br₂]) by subtracting the concentration at the later time from the concentration at the earlier time, since Br₂ is being consumed.

Determine the change in time (Δt) corresponding to the concentration change, using the time interval around 25 seconds.

Calculate the instantaneous rate of the reaction at 25 s by finding the slope of the tangent to the concentration vs. time curve at 25 s, which can be approximated by Δ[Br₂]/Δt over the small interval around 25 s.

Express the rate as a positive value and remember that the rate of disappearance of Br₂ is related to the rate of the reaction; since the reaction consumes Br₂, the rate = - (d[Br₂]/dt).

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Instantaneous Rate of Reaction

The instantaneous rate of a reaction is the rate at a specific moment in time, found by determining the slope of the tangent line to the concentration vs. time curve at that point. It reflects how fast the concentration of a reactant or product changes at that exact time.

Concentration vs. Time Graph Interpretation

A concentration vs. time graph shows how the amount of a reactant or product changes during a reaction. The slope of the curve at any point indicates the rate of change of concentration, which is essential for calculating reaction rates.

Rate of Reaction and Stoichiometry

The rate of reaction is often expressed in terms of the change in concentration of reactants or products per unit time, adjusted by their stoichiometric coefficients. Understanding the balanced equation helps relate the rate of disappearance of Br2 to the overall reaction rate.

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