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Ch.14 - Chemical Kinetics
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Not the one you use?Change textbook
All textbooksBrown 14th EditionCh.14 - Chemical KineticsProblem 3a
Chapter 14, Problem 3a

You study the rate of a reaction, measuring both the concentration of the reactant and the concentration of the product as a function of time, and obtain the following results:
Graph showing concentration of reactant C decreasing and product D increasing over time.
Which chemical equation is consistent with these data: (i) A → B, (ii) B → A, (iii) A → 2 B, (iv) B → 2 A?

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1
Examine the graph and note that the concentration of reactant C decreases over time while the concentration of product D increases over time.
Identify that the reaction is proceeding in the forward direction, converting reactant C into product D.
Consider the stoichiometry of the reaction. Since the concentration of C decreases and D increases, the reaction must involve a single reactant converting into a single product or multiple products.
Compare the given chemical equations: (i) A → B, (ii) B → A, (iii) A → 2 B, (iv) B → 2 A.
Determine that the correct equation must reflect the observed changes in concentration. Since the graph shows a one-to-one correspondence between the decrease in C and the increase in D, the most consistent equation is (i) A → B.

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Key Concepts

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

Reaction Rate

The reaction rate refers to the speed at which reactants are converted into products in a chemical reaction. It is typically expressed as the change in concentration of a reactant or product over time. Understanding how concentration changes over time helps in determining the direction of the reaction and the stoichiometry involved.
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Chemical Equilibrium

Chemical equilibrium occurs when the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products. In the context of the provided graph, the concentrations of reactant C decrease while product D increases, indicating a shift towards product formation, which is essential for identifying the correct chemical equation.
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Stoichiometry

Stoichiometry involves the quantitative relationships between reactants and products in a chemical reaction, as described by the balanced chemical equation. It allows for the prediction of how changes in concentration will affect the amounts of reactants and products, which is crucial for interpreting the data shown in the graph and selecting the appropriate reaction equation.
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Related Practice
Textbook Question

The following diagrams represent mixtures of NO(g) and O21g2. These two substances react as follows: 2 NO1g2 + O21g2¡2 NO21g2 It has been determined experimentally that the rate is second order in NO and first order in O2. Based on this fact, which of the following mixtures will have the fastest initial rate? [Section 14.3]

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Textbook Question

Consider the following graph of the concentration of a substance X over time. Is each of the following statements true or false? (d) As time progresses, the curve will eventually turn downward toward the x-axis. [Section 14.2]

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Textbook Question

An automotive fuel injector dispenses a fine spray of gasoline into the automobile cylinder, as shown in the bottom drawing here. When an injector gets clogged, as shown in the top drawing, the spray is not as fine or even and the performance of the car declines. How is this observation related to chemical kinetics? [Section 14.1]

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Textbook Question

Given the following diagrams at t = 0 min and t = 30 min

After four half-life periods for a first-order reaction, what fraction of reactant remains? [Section 14.4]

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