Elementary Step Rate Laws: Intermediates Included?

The rate law of a reaction is derived from its slowest elementary step, also known as the rate-determining step. The rate law describes the relationship between the reactants' concentration and the reaction rate. While intermediates are formed during the reaction mechanism, they do not appear in the final rate law expression. However, the rate law can include intermediate concentrations if they influence the reaction rate. The elementary steps must add up to the overall reaction, and the rate-determining step limits the overall rate.

Intermediates are formed but don't appear in the final rate law expression

In chemistry, a rate law describes the relationship between the rate of a reaction and the concentrations of reactants involved. The rate law of a reaction can be determined from the slowest elementary step, also known as the rate-determining step.

Intermediates are molecules or elements that are formed and consumed during the course of a reaction mechanism. They are first produced and then used up in the following or another step. They are present in the products and reactants side of the chemical equation and hence cancel out, not appearing in the final rate law expression.

While intermediates are not part of the overall rate law expression for a complete reaction, their concentrations can appear in rate laws when they play a critical role in individual steps of the reaction mechanism. Intermediates may appear in the rate law for specific steps of a reaction mechanism, especially if they are significant in the rate-determining step.

For example, consider a reaction mechanism where an intermediate A transforms into a product B. If step 2 includes intermediate A and is the rate-determining step, then the concentration of A could be significant to express how fast the products are formed, and thus may appear in the rate law for that specific step.

Intermediates are molecules or elements found in the product of one step

In chemistry, a reaction intermediate, or simply an intermediate, is a molecule or compound that arises within the sequence of a stepwise chemical reaction. Intermediates are formed as the reaction product of an elementary step from the reactants and/or preceding intermediates but are consumed in a later step. In other words, they are molecules or elements found in the product of one step and are then used as reactants in a subsequent step. Importantly, they do not appear in the overall reaction equation.

For example, in the reaction:

> H2 + Br2 -> 2HBr

Br and H are the intermediates. However, they will cancel each other out and will not appear in the overall reaction.

Intermediates are created in one step and then consumed in a later step. They are not present at the end of the reaction but are used along the way. For instance, in a reaction where A turns into products through a mechanism that includes a slow step involving A and an intermediate B, the reaction rate can be expressed as k [A], where k is the rate constant. Here, B is an intermediate not present in the overall reaction equation.

The rate law of a reaction can be determined from the slowest elementary step, also known as the rate-determining step. While there is some debate on whether the rate law of the overall reaction can include intermediates, it is generally accepted that they do not appear in the final rate law expression.

The rate law can be determined from the slowest elementary step

The rate law of a reaction is determined by the slowest elementary step, also known as the rate-determining step. This is the slowest step within a chemical reaction, and it determines the rate of the chemical reaction. For instance, in a reaction where A turns into products through a mechanism that includes a slow step involving A and an intermediate B, the rate law is based on A since B is an intermediate not present in the overall reaction equation.

The rate law describes the relationship between the concentration of reactants and the rate of the reaction. It can be written as rate = rate constant x [concentration of reactant]^reaction order. For example, in the reaction of carbon monoxide and nitrogen dioxide to form carbon dioxide and nitrogen oxide, the rate equation is usually given as r=k [NO2] [CO]. However, if this reaction occurs in multiple steps, and the rate of the first step is slower than that of the second step, the rate equation becomes r = k [NO2]^2.

The slowest elementary step can be determined by setting up a reaction mechanism. In a reaction mechanism, reactants become products in a series of elementary steps. For example, in a reaction with two elementary steps, if the first step has a rate constant of k1 and the second step has a rate constant of k2, and k1 < k2, then the first step is the slowest.

While intermediates are formed during the reaction mechanism, they do not appear in the final rate law expression.

The rate of the overall reaction is determined by the slowest step

The rate of a multi-step reaction is determined by the slowest elementary step, also known as the rate-determining step. This slowest step limits the overall rate of the reaction. The rate equation is derived by the slowest step in the reaction. The rate law of a reaction can be determined from the slowest elementary step, also known as the rate-determining step. The rate law describes the relationship between the concentration of reactants and the rate of the reaction.

The rate law of the overall reaction can include intermediates. Intermediates are species that are formed and consumed during the reaction but do not appear in the overall balanced equation. The rate law can include the concentrations of intermediates if they affect the rate of the reaction. However, according to some sources, while intermediates are formed during the reaction mechanism, they do not appear in the final rate law expression. Intermediates are molecules or elements that are found in the product of one step but are also located in the reactant of another step.

For example, in the reaction of carbon monoxide and nitrogen dioxide to form carbon dioxide and nitrogen oxide, the rate equation would usually be r=k[NO2][CO] as the rate depends on the reaction of the nitrogen dioxide and carbon monoxide in a one-step reaction. But if this was a multistep reaction and it was actually dependent on the collision of two nitrogen dioxide molecules, the rate of reaction would be r = k[NO2]2. The fact that the experimentally determined rate law does not match the rate law derived from the overall reaction equation suggests that the reaction occurs over multiple steps.

The rate law can include intermediate concentrations if they affect the rate of reaction

The rate law of a reaction is determined by the slowest elementary step, also known as the rate-determining step. This slowest step dictates the overall rate of the reaction. The rate law describes the relationship between the concentration of reactants and the rate of the reaction.

The rate law can include intermediate concentrations if they affect the rate of the reaction. Intermediates are molecules or elements that are formed and consumed during the reaction but do not appear in the overall balanced equation. They are fleeting and often go unobserved, but their concentration can be worked out indirectly. For example, the concentration of the trityl cation, a known reactive intermediate, can be calculated by knowing that it is produced by trityl chloride, which can be measured and added to the reaction mixture.

However, some sources state that intermediates are not included in the final rate law expression. This is because they are not present in the overall reaction equation, and so the rate law is based solely on the reactants involved in the slow step. For example, in the reaction where A turns into products through a mechanism that includes a slow step involving A and an intermediate B, the rate law is based solely on A.

In some cases, intermediates can be eliminated from the rate equation using the equilibrium condition.

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