The rate of reaction in terms of the "rate law expression" includes the rate constant (k), the concentration of the reactants, and the orders of the reaction with respect to the different reactants. Consider the following reaction: A+BâC+D The initial concentrations of the reactants A and B are 0.240 M and 0.400 M, respectively. The rate of reaction is 0.060 Mâ sâ1, and the orders of the reaction, with respect to reactants A and B, are 1 and 2, respectively. Determine the rate constant (k) for the reaction using the rate law. Express your answer in Mâ2â sâ1 to three significant figures.
The rate of reaction in terms of the "rate law expression" includes the rate constant (k), the concentration of the reactants, and the orders of the reaction with respect to the different reactants. Consider the following reaction: A+BâC+D The initial concentrations of the reactants A and B are 0.240 M and 0.400 M, respectively. The rate of reaction is 0.060 Mâ sâ1, and the orders of the reaction, with respect to reactants A and B, are 1 and 2, respectively. Determine the rate constant (k) for the reaction using the rate law. Express your answer in Mâ2â sâ1 to three significant figures.
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Related questions
Learning Goal:
To understand reaction order and rate constants.
For the general equation aA+bBâcC+dD, the rate law is expressed as follows:
rate=k[A]m[B]n
where m and n indicate the order of the reaction with respect to each reactant and must be determined experimentally and k is the rate constant, which is specific to each reaction.
Order
For a particular reaction, aA+bB+cCâdD, the rate law was experimentally determined to be
rate=k[A]0[B]1[C]2=k[B][C]2
This equation is zero order with respect to A. Therefore, changing the concentration of A has no effect on the rate because [A]0 will always equal 1.(Figure 1)
This equation is first order with respect to B. This means that if the concentration of B is doubled, the rate will double. If [B] is reduced by half, the rate will be halved. If [B] is tripled, the rate will triple, and so on.(Figure 2)
This equation is second order with respect to C. This means that if the concentration of C is doubled, the rate will quadruple. If [C] is tripled, the rate will increase by a factor of 9, and so on.
Overall reaction order and rate-constant units
The sum of the individual orders gives the overall reaction order. The example equation above is third order overall because 0+1+2=3.
For the units of rate to come out to be M/s, the units of the rate constant for third-order reactions must be Mâ2â sâ1 since
M/s=(Mâ2â sâ1)(M3)
For a second-order reaction, the rate constant has units of Mâ1â sâ1 because M/s=(Mâ1â sâ1)(M2). In a first-order reaction, the rate constant has the units sâ1because M/s=(sâ1)(M1).
Analyzing a specific reaction
Consider the following reaction:
2H2+2NOâN2+2H2O,rate=k[H2][NO]2
Part A
What is the overall reaction order?
Express your answer as an integer.
What are the units of the rate constant k for this reaction?
choose one
What are the units of the rate constant for this reaction?
| Mâ sâ1 |
| sâ1 |
| Mâ1â sâ1 |
| Mâ2â sâ1 |
| Mâ3â sâ1 |
Part C
What would happen to the rate if [H2] were doubled?
View Available Hint(s)
The rate would
What would happen to the rate if were doubled?
| stay the same. | ||||
| double. | ||||
| triple. | ||||
| quadruple. What would happen to the rate if [NO] were doubled? View Available Hint(s) The rate would What would happen to the rate if were doubled?
|
