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What is the rate law for the elementary termolecular reaction \(A+2 B \longrightarrow\) products? For \(3 A \longrightarrow\) products?

Short Answer

Expert verified
The rate law for the reaction \(A + 2B \longrightarrow \text{products}\) is \(\text{Rate} = k[A][B]^2\). For the reaction \(3A \longrightarrow \text{products}\), the rate law is \(\text{Rate} = k[A]^3\).

Step by step solution

01

Identifying the Rate Law of a Termolecular Reaction with Molecule A and Two Molecules of B

For an elementary reaction such as \(A + 2B \longrightarrow \text{products}\), the rate law is determined by the stoichiometry of the reactants in the balanced chemical equation. As this is an elementary step, the rate law is simply the product of the concentration of the reactants each raised to the power of their stoichiometric coefficients. Therefore, the rate law for the reaction is: \(\text{Rate} = k[A][B]^2\), where \(k\) is the rate constant for the reaction.
02

Identifying the Rate Law for the Termolecular Reaction Involving Three Molecules of A

Similarly, for the reaction \(3A \longrightarrow \text{products}\), the rate law follows the stoichiometry of the elementary reaction. Thus, the rate law for this reaction is: \(\text{Rate} = k[A]^3\), where \(k\) again denotes the rate constant.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Termolecular Reaction
When studying chemical reactions, it's crucial to understand the types of molecular interactions that lead to product formation. A termolecular reaction involves a three-molecule collision leading to a reaction. These types of reactions are quite rare because the probability of three particles colliding simultaneously with the right orientation and sufficient energy is very low. In the context of the exercise, an example of a termolecular reaction is when one molecule of 'A' and two molecules of 'B' react together. Despite these reactions being less common, understanding how they occur helps us appreciate the complexity of chemical kinetics and the specific conditions required for successful reactions.

Studying termolecular reactions can be intriguing as they provide insights into reaction mechanisms that are more complex than simple bimolecular interactions. Scientists explore these reactions in detailed mechanisms that often involve multiple steps, where the actual termolecular step might be an intermediate step in a sequence leading to the overall reaction products. Thus, termolecular reactions play a key role in deeper explorations of reaction dynamics.
Reaction Stoichiometry
Reaction stoichiometry is the quantitative relationship between reactants and products in a chemical reaction. It's defined by the balanced chemical equation which provides a ratio of how many moles of each reactant are required to produce a given number of moles of product. In the given exercise, the stoichiometry shows one molecule of 'A' reacting with two molecules of 'B', highlighting that 'B' is used twice as much as 'A' in the reaction.

This concept becomes especially important when calculating the rate law for a reaction, as the rate law expresses the speed of a reaction in terms of the concentration of the reactants, raised to the power of their stoichiometric coefficients. Understanding reaction stoichiometry allows students not only to predict the outcomes of reactions but also to manipulate conditions to achieve desired results. Mastery of stoichiometry is therefore essential in the field of chemistry, as it is the basis for creating buffers, manufacturing drugs, or even predicting the environmental impact of chemical processes.
Rate Constant
At the heart of understanding chemical kinetics is the concept of the rate constant, symbolized as 'k'. The rate constant is a proportionality factor in the rate law of a reaction that provides the relationship between reactant concentrations and the rate of the reaction. It is influenced by factors such as temperature, presence of catalysts, and the inherent properties of the reactants.

In the example provided by the exercise, the rate laws for the two termolecular reactions include the rate constant 'k'. This constant will vary for different reactions and under different conditions. A higher 'k' value generally indicates a faster reaction, given the same concentrations of reactants. Knowing the rate constant of a reaction can help chemists control the speed of the reaction, which is critical in industries like pharmaceuticals where reaction times can impact the quality and effectiveness of a drug product. Thus, learning to calculate and interpret 'k' is invaluable for students aiming to apply chemistry in practical situations.

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Most popular questions from this chapter

Some bacteria are resistant to the antibiotic penicillin because they produce penicillinase, an enzyme with a molecular weight of \(3 \times 10^{4} \mathrm{g} / \mathrm{mol}\) that converts penicillin into inactive molecules. Although the kinetics of enzyme-catalyzed reactions can be complex, at low concentrations this reaction can be described by a rate law that first order in the catalyst (penicillinase) and that also involves the concentration of penicillin. From the following data: \(1.0 \mathrm{L}\) of a solution containing \(0.15 \mu \mathrm{g}\left(0.15 \times 10^{-6} \mathrm{g}\right)\) of penicillinase, determine the order of the reaction with respect to penicillin and the value of the rate constant. $$\begin{array}{|c|c|} \hline \text { [Penicillin] (M) } & \text { Rate \(\left(\mathrm{mol} \mathrm{L}^{-1} \mathrm{min}^{-1}\right)\) } \\ \hline 2.0 \times 10^{-6} & 1.0 \times 10^{-10} \\ \hline 3.0 \times 10^{-6} & 1.5 \times 10^{-10} \\ \hline 4.0 \times 10^{-6} & 2.0 \times 10^{-10} \\\ \hline \end{array}$$

In the nuclear industry, chlorine trifluoride is used to prepare uranium hexafluoride, a volatile compound of uranium used in the separation of uranium isotopes. Chlorine trifluoride is prepared by the reaction \(\mathrm{Cl}_{2}(g)+3 \mathrm{F}_{2}(g) \longrightarrow 2 \mathrm{ClF}_{3}(g) .\) Write the equation that relates the rate expressions for this reaction in terms of the disappearance of \(\mathrm{Cl}_{2}\) and \(\mathrm{F}_{2}\) and the formation of \(\mathrm{ClF}_{3}\).

What is the half-life for the first-order decay of carbon-14? $$\left(\begin{array}{c}14 \\\6\end{array} \mathbf{C} \longrightarrow_{7}^{14} \mathbf{N}+\mathrm{e}^{-}\right)$$ The rate constant for the decay is \(1.21 \times 10^{-4}\) year \(^{-1}\).

Regular flights of supersonic aircraft in the stratosphere are of concern because such aircraft produce nitric oxide, NO, as a byproduct in the exhaust of their engines. Nitric oxide reacts with ozone, and it has been suggested that this could contribute to depletion of the ozone layer. The reaction \(\mathrm{NO}+\mathrm{O}_{3} \longrightarrow \mathrm{NO}_{2}+\mathrm{O}_{2}\) is first order with respect to both \(\mathrm{NO}\) and \(\mathrm{O}_{3}\) with a rate constant of \(2.20 \times 10^{7} \mathrm{L} / \mathrm{mol} / \mathrm{s}\). What is the instantaneous rate of disappearance of NO when \([\mathrm{NO}]=3.3 \times 10^{-6} \mathrm{M}\) and \(\left[\mathrm{O}_{3}\right]=5.9 \times 10^{-7} \mathrm{M} ?\)

How does an increase in temperature affect rate of reaction? Explain this effect in terms of the collision theory of the reaction rate.

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