Chapter 2: Problem 16
For the stoichiometry \(A+B \rightarrow(\) products) find the reaction orders with respect to \(A\) and \(B\). $$\begin{array}{c|ccc}C_{\mathrm{A}} & 4 & 1 & 1 \\\C_{\mathrm{B}} & 1 & 1 & 8 \\\\-r_{\mathrm{A}} & 2 & 1 & 4 \end{array}$$
Short Answer
Expert verified
The reaction order with respect to A is 1/2, and the reaction order with respect to B is 2/3.
Step by step solution
01
Understanding the Rate Law
The rate of reaction with respect to each reactant can be represented by a rate law. The rate law for a reaction A + B → Products can be written as Rate = k*[A]^x*[B]^y, where x and y are the reaction orders with respect to A and B, respectively, and k is the rate constant.
02
Analyzing the Given Data
We have been given a set of experimental data where the concentrations of A and B and the rate of reaction (-r_A) are varied. We will use this information to determine the reaction orders x and y.
03
Finding the Reaction Order with Respect to A
Comparing experiments 1 and 2 where the concentration of B is kept constant, the concentration of A changes from 4 to 1, and the rate of reaction changes from 2 to 1. If we write the rate as a function of A's concentration for the first and second experiments, we have 2 = k*4^x and 1 = k*1^x. Dividing these equations, we get (2/1) = (4/1)^x, which simplifies to 2 = 4^x. Solving for x gives x = 1/2.
04
Finding the Reaction Order with Respect to B
Comparing experiments 2 and 3 where the concentration of A is constant, the concentration of B changes from 1 to 8, and the rate of reaction changes from 1 to 4. Writing the rate as a function of B's concentration for the second and third experiments, we have 1 = k*1^y and 4 = k*8^y. Dividing these equations, we get (4/1) = (8/1)^y, which simplifies to 4 = 8^y. Solving for y gives y = 2/3.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Rate Law
Understanding the rate law is crucial for deciphering the dynamics of a chemical reaction. In essence, the rate law is an equation that relates the rate of a chemical reaction to the concentration of its reactants. The general form of a rate law is Rate = k*[A]x*[B]y, where:
Experimentation plays a pivotal role in determining these reaction orders. By observing how varying concentrations of reactants influence the reaction rate, it's possible to deduce the power to which the concentration of a given reactant must be raised, thereby revealing its order within the rate law. Moreover, the reaction orders x and y are usually (but not always) whole numbers and can be zero, indicating the reaction rate is unaffected by the concentration of that particular reactant.
- k is the reaction rate constant, unique to each reaction and dependent on temperature.
- [A] and [B] represent the molar concentrations of reactants A and B, respectively.
- x and y are the reaction orders which indicate how the rate is affected by changes in the concentration of each reactant.
Experimentation plays a pivotal role in determining these reaction orders. By observing how varying concentrations of reactants influence the reaction rate, it's possible to deduce the power to which the concentration of a given reactant must be raised, thereby revealing its order within the rate law. Moreover, the reaction orders x and y are usually (but not always) whole numbers and can be zero, indicating the reaction rate is unaffected by the concentration of that particular reactant.
Chemical Kinetics
Chemical kinetics is the study of reaction rates and the factors that affect them. It's a branch of physical chemistry that delves into the speed at which chemical reactions occur and the steps through which they proceed. A few key points to consider are:
Chemical kinetics also involves the study of conditions that affect reaction rates, such as temperature and the presence of catalysts, which can lower the activation energy of a reaction. Understanding these concepts allows chemists to control and optimize reactions for various applications, from industrial synthesis to enzyme regulation in biological systems.
- Reaction Rate: The speed at which reactants convert to products. This can be measured by the change in concentration of a reactant or product per unit time.
- Rate Law: An expression that provides a quantitative description of the reaction rate.
- Reaction Order: A component of the rate law; indicates the dependency of the reaction rate on the concentration of each reactant.
- Activation Energy: The energy needed to initiate the reaction. It's one of several factors that can influence reaction rates.
Mechanisms and Pathways
Chemical reactions often proceed through a series of steps known as the reaction mechanism. Each step involves a transition state with a certain activation energy, and the slowest step in the sequence is the rate-determining step.
Chemical kinetics also involves the study of conditions that affect reaction rates, such as temperature and the presence of catalysts, which can lower the activation energy of a reaction. Understanding these concepts allows chemists to control and optimize reactions for various applications, from industrial synthesis to enzyme regulation in biological systems.
Stoichiometry
Stoichiometry is the quantitative relationship between reactants and products in a chemical reaction. It is based on the law of conservation of mass, which states that matter is neither created nor destroyed in a chemical reaction. Hence, stoichiometry involves calculations that allow chemists to predict the amounts of substances consumed and produced in a reaction. Key points include:
Stoichiometry is not only essential for predicting product yields but also for scaling reactions to different sizes – from laboratory research to industrial production. It provides a bridge between the molecular scale and the real-world scale at which we experience chemical reactions and processes.
- Mole Ratio: Derived from the coefficients of a balanced chemical equation, the mole ratio is critical for converting between moles of one reactant or product and another.
- Limiting Reagent: The reactant that will be completely consumed first, thus determining the amount of product formed.
- Theoretical Yield: The maximum amount of product that can be formed from a given amount of reactants.
- Actual Yield: The amount of product actually produced when the reaction is carried out in a laboratory or industrial setting.
- Percentage Yield: A comparison of the actual yield to the theoretical yield, expressed as a percentage.
Stoichiometry is not only essential for predicting product yields but also for scaling reactions to different sizes – from laboratory research to industrial production. It provides a bridge between the molecular scale and the real-world scale at which we experience chemical reactions and processes.