The Rate Law and Its Components Flashcards
For a reaction at a fixed temperature
aA + bB … –> cC + dD …, what is the Rate Law?
Rate = k[A]^m [B]^n …
In the rate law, what is k?
The rate constant, which relates reaction rate to reactant (and product concentrations). It is specific for a given reaction at a given temperature
In the rate law, what are m and n?
Reaction orders
What do reaction orders define?
How a reaction rate is affected by reactant concentrations
What differs between the rate law and the general expression of rate?
The rate law also tells how reaction rate changes with concentration.
Is reaction rate proportional to concentration?
Not always
Does reaction order refer to each reactant or the overall reaction?
Both. There are reaction orders of reactants and of the overall reaction
How do you find the overall reaction order?
Add the reaction orders of individual reactants
If the reaction order is zero with respect to [A], what happens to the rate when [A] doubles?
The rate does not change. Zero order means rate is independent of concentration
If the reaction is 1st order with respect to [A], what happens to the rate when [A] doubles?
The rate doubles
If the reaction is 2nd order with respect to [A], what happens to the rate when [A] doubles?
The rate quadruples
If a reaction is 1/2 order with respect to [A], what happens to the rate when [A] quadruples?
The rate doubles
If a reaction is -1st order with respect to [A], what happens to the rate when [A] doubles?
The rate is half as fast
Can you determine reaction orders from a balanced chemical equation?
No, they are determined by experimentation
Rate = k[A]^2
What is the reaction order?
2nd order
Rate = k
What is the reaction order?
Zero order
Rate = k[A][B]
What is the overall reaction order?
2nd order
Rate = k[A]
What is the overall reaction order?
1st order
Rate = k[A][B]^2
What is the overall reaction order?
Third order
What is a negative reaction order?
When the rate decreases as the concentration of a component increases.
If rate = k[A]^2, by what factor does the rate change if [A] is tripled?
By a factor of 9 (3^2 = 9)
If rate = k[A]^2 [B], by what factor does the rate change if both [A] and [B] are doubled?
By a factor of 8
Rate = k(2^2)(2) = k(4)(2) = 8k
What is the general formula for units of k?
[(L/mol)^(overall order - 1)] / (unit of t)
What are the units of k for a zero order reaction?
mol/L⋅s
What are the units of k for a first order reaction?
1/s or s^-1
What are the units of k for a second order reaction?
L/mol⋅s
What are the units of k for a third order reaction?
L^2/(mol^2 ⋅ s)
For rate = k[A]^2, if [A] is halved, by what factor is the initial rate changed?
The rate would be 1/4 of the initial rate
(1/2)^2 = 1/4
