Integrated Rate Law for 2nd Order Reactions

In summary, the conversation discusses the concept of rate of reaction and how it is defined as the speed of change of concentration. It is often expressed as (1/a)*d[A]/dt, where a is the stoichiometric coefficient of A. This means that the rate of reaction can vary depending on how the equation is written. The preference is to talk about the rate of change of concentration of a specified reagent.
  • #1
samy4408
62
9
hello i have a question about kinetics : to have the integrated rate law for second order reaction the professor write the following
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why we don't write the rate like this : rate = -1/2(d[1]/dt) ?
why we ignore the stoichiometric coefficient ?
 
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  • #2
Rate is defined as a speed of change of the concentration, period.
 
  • #3
"Rate of reaction" is often defined as (1/a)*d[A]/dt, where a is the stoichiometric coefficient of A (negative for reactants, positive for products). Then it's the same whichever reagent you look at, but it depends how you write the equation, e.g. it would be different for A → ½B or 4A → 2B. My preference is always to talk in terms of the rate of change of concentration of a specified reagent.
 

FAQ: Integrated Rate Law for 2nd Order Reactions

1. What is the Integrated Rate Law for 2nd Order Reactions?

The Integrated Rate Law for 2nd Order Reactions is a mathematical expression that describes the relationship between the concentration of a reactant and time for a second-order reaction. It is derived from the rate law for a second-order reaction and allows for the determination of the rate constant and half-life of the reaction.

2. How is the Integrated Rate Law for 2nd Order Reactions derived?

The Integrated Rate Law for 2nd Order Reactions is derived by integrating the rate law for a second-order reaction, which is rate = k[A]². The integration process involves separating the variables, integrating both sides of the equation, and solving for the concentration of the reactant as a function of time.

3. What is the general form of the Integrated Rate Law for 2nd Order Reactions?

The general form of the Integrated Rate Law for 2nd Order Reactions is: 1/[A]t = kt + 1/[A]0, where [A]t is the concentration of the reactant at time t, k is the rate constant, and [A]0 is the initial concentration of the reactant.

4. How is the Integrated Rate Law for 2nd Order Reactions used to determine the rate constant and half-life?

The Integrated Rate Law for 2nd Order Reactions can be rearranged to the form ln([A]t/[A]0) = -kt, which is a linear equation with a slope of -k and a y-intercept of ln([A]0/[A]t). By plotting ln([A]t/[A]0) against time, the rate constant can be determined from the slope of the line. The half-life can be calculated by using the equation t1/2 = 1/(k[A]0), where t1/2 is the half-life and [A]0 is the initial concentration of the reactant.

5. What are the units of the rate constant in the Integrated Rate Law for 2nd Order Reactions?

The units of the rate constant in the Integrated Rate Law for 2nd Order Reactions depend on the overall order of the reaction. For a second-order reaction, the units of the rate constant are M⁻¹s⁻¹, where M is the unit for concentration and s is the unit for time.

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