Chapter 2: Problem 17
For the stoichiometry \(A+B \rightarrow(\) products) find the reaction orders with respect to \(A\) and \(B\). $$\begin{array}{c|rrr}C_{\mathrm{A}} & 2 & 2 & 3 \\\C_{\mathrm{B}} & 125 & 64 & 64 \\\\-r_{\mathrm{A}} & 50 &32 & 48\end{array}$$
Short Answer
Expert verified
The reaction orders are both 1 with respect to concentrations of A \(C_{A}\) and B \(C_{B}\).
Step by step solution
01
Define the Reaction Order
The reaction order with respect to a reactant is the exponent to which its concentration is raised in the rate law equation. The rate law for a reaction where A and B are reactants can be generally expressed as: \(rate = k[C_{A}]^{n}[C_{B}]^{m}\) Here, \(n\) and \(m\) are the reaction orders with respect to \(A\) and \(B\), respectively, and \(k\) is the rate constant.
02
Analyze Given Data for A
Compare experiments where \(C_{B}\) is constant to find the order with respect to \(A\). In the table, experiments 2 and 3 have constant \(C_{B}\) values. The rate of reaction for these is denoted by \(-r_{A}\).We can calculate the relative rate change from experiment 2 to 3 as follows:\(\frac{-r_{A3}}{-r_{A2}} = \frac{48}{32} \)This simplifies to \(\frac{3}{2}\).Similarly, the change in \(C_{A}\) from experiment 2 to 3 is \(\frac{C_{A3}}{C_{A2}} = \frac{3}{2}\).Since the rates change by the same factor as changes in \(C_A\) when \(C_B\) is constant, the reaction order with respect to \(A\) is 1.
03
Analyze Given Data for B
Compare experiments where \(C_{A}\) is constant to find the order with respect to \(B\). In the table, experiments 1 and 2 have constant \(C_{A}\) values. We can calculate the relative rate change from experiment 1 to 2 as follows:\(\frac{-r_{A2}}{-r_{A1}} = \frac{32}{50} \)This simplifies to \(\frac{8}{25} \).The change in \(C_{B}\) from experiment 1 to 2 is\(\frac{C_{B2}}{C_{B1}} = \frac{64}{125}\).This simplifies to \(\frac{8}{25}\).Thus, the rates change by the same factor as changes in \(C_B\) when \(C_A\) is constant, indicating that the reaction order with respect to \(B\) is also 1.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Rate Law Equation
Understanding the rate law equation is fundamental for grasping the principles underlying chemical kinetics. The rate law reveals how the rate of a chemical reaction is affected by the concentration of its reactants. In its general form, for a reaction involving reactants A and B, the rate law is expressed as:
\[ rate = k[C_A]^{n}[C_{B}]^{m} \]
where:
\[ rate = k[C_A]^{n}[C_{B}]^{m} \]
where:
- \( k \) is the rate constant of the reaction,
- \( [C_A] \) and \( [C_B] \) are the concentrations of reactants A and B, respectively,
- \( n \) is the reaction order with respect to A,
- and \( m \) is the reaction order with respect to B.
Chemical Reaction Stoichiometry
Chemical reaction stoichiometry is concerned with the quantitative relationships between the amounts of reactants and products in a chemical reaction. It relies on the balanced chemical equation to determine the proportion of molecules or moles involved in the reaction. The stoichiometry does not directly inform the speed of the reaction — this is where the rate law becomes essential.
Even though the stoichiometric coefficients suggest a specific ratio in which reactants are consumed and products are formed, they do not indicate how quickly this occurs. The rate law, with its reaction order, addresses this by showing how the rate responds to changes in reactant concentrations. Through problems like the textbook exercise, where students deduce reaction orders, it becomes clear that stoichiometry and kinetics must both be considered to fully understand a chemical reaction's behavior.
Even though the stoichiometric coefficients suggest a specific ratio in which reactants are consumed and products are formed, they do not indicate how quickly this occurs. The rate law, with its reaction order, addresses this by showing how the rate responds to changes in reactant concentrations. Through problems like the textbook exercise, where students deduce reaction orders, it becomes clear that stoichiometry and kinetics must both be considered to fully understand a chemical reaction's behavior.
Concentration Dependency
The concept of concentration dependency is integral in the study of reaction kinetics. It deals with how the changes in the concentration of reactants influence the rate of a chemical reaction. Chemical kinetics focuses on the speed of a reaction, and the rate law establishes that the rate often depends on the concentrations of reactants to a certain power—the reaction order.
The reaction rate increases when the concentration of a reactant is raised, but the extent of this increase depends on the reaction order. For example, a reaction order of 1 implies that if the concentration of a reactant is doubled, so is the rate. However, if the order is 2, doubling the concentration would quadruple the reaction rate. This dependency on concentration is not always straightforward, thereby making experiments and calculations, such as those provided in the exercise, crucial for determining the relationship between reactant concentration and reaction rate.
The reaction rate increases when the concentration of a reactant is raised, but the extent of this increase depends on the reaction order. For example, a reaction order of 1 implies that if the concentration of a reactant is doubled, so is the rate. However, if the order is 2, doubling the concentration would quadruple the reaction rate. This dependency on concentration is not always straightforward, thereby making experiments and calculations, such as those provided in the exercise, crucial for determining the relationship between reactant concentration and reaction rate.
Chemical Kinetics
Chemical kinetics is the branch of chemistry that studies the speed or rate of chemical reactions. It also involves the factors that influence this speed and the mechanisms by which the reactions proceed. The experimental data from the textbook exercise help us explore these aspects of kinetics.
By analyzing how the reaction rate changes when the concentrations of reactants A and B are varied, we delve into the practical application of chemical kinetics. The reaction orders derived give us an understanding of how sensitive the reaction is to changes in concentration. Moreover, kinetics is not only about calculating these orders; it's also about understanding the molecular dynamics and energy profile of a reaction, thus painting a complete picture of how reactions run their course. Obtaining the reaction orders is one of the first steps in this broader field, which ultimately allows chemists to control and optimize reactions for various practical applications.
By analyzing how the reaction rate changes when the concentrations of reactants A and B are varied, we delve into the practical application of chemical kinetics. The reaction orders derived give us an understanding of how sensitive the reaction is to changes in concentration. Moreover, kinetics is not only about calculating these orders; it's also about understanding the molecular dynamics and energy profile of a reaction, thus painting a complete picture of how reactions run their course. Obtaining the reaction orders is one of the first steps in this broader field, which ultimately allows chemists to control and optimize reactions for various practical applications.