Rate Laws
Definition: The expression of the relationship between the rate of a reaction to
the rate constant and the reactant concentration raised to some powers, rate
law uses experimental values.
Rate law equation format: r=k[A]x[B]y
- r = Rate
- k = Rate constant
- [ ] = Concentration
- [A] & [B] = Concentration value of component A & B
- x & y = Reaction orders of given component
Reaction Orders (0 to 3)
Reaction orders are the values of x and y in the rate law equation, and expresses
the effect of the concentration change of a single reactant on the final
reaction rate.
Zero order:
- A0 = 1
- 20 = 1
- When concentration doubles, rate doesn’t change.
- Altering in concentrations does not affect overall reaction rate, as any
values to the power of zero equals one, therefore will not see a change in
result.
- Ex. [I-]0 does not need to be included in the rate law equation, as it
wouldn’t affect the final rate.
First order:
- A1 = 2
- 21 = 2
- Doubling in concentration lead to doubling in reaction rate.
Second order:
- A2 = 4
- 22 = 4
- Doubling in concentration leads to quadrupling in rate.
Third order:
- A3 = 8
- 23 = 8
, - Doubling in concentration leads to octuple in rate.
*Note: A will not always be 2, but whatever the concentration is going up
by to the power of whatever the change in rate is. See example below *
[F2] (M) [ClO2] (M) Initial Rate (M/s)
0.10 0.010 0.0012
0.10 0.040 0.0048
0.20 0.010 0.0024
Note that when calculating the reaction order for [ClO2], the rate value went
from 0.0012 to 0.0048 when the concentration quadrupled, meaning that the
change in concentration is equivalent to the change in rate.
Referring back to the previous orders law, we can see that when 2 is to the
power of 1, the rate equals 2, meaning that the concentration change and rate
change is equal to each other, defined as the first order.
Same idea applies to this example as well, when [ClO2] quadruples, the rate
quadruples as well, keeping the proportion of the reaction order rules, we can
see it as 41, or first order reaction.
Important: When calculating reaction orders for one component, ALWAYS
make sure that the concentration of the other component remains unchanged.
DO NOT use two trials with different values for both components.
Rate Law Calculations
Equation: r = k[A]x[B]y
When calculating for rate law, experimental values will always be given, and
the equation is usually manipulated/rearranged to solve for k.
Ex:
Trial # Intial [A] Initial [B] Initial Rate
1 1.00 M 1.00 M 1.25 × 10-2 M/s
2 1.00 M 2.00 M 2.50 × 10-2 M/s
3 2.00 M 2.00 M 2.50 × 10-2 M/s
Calculate for:
- Rate Law equation
Definition: The expression of the relationship between the rate of a reaction to
the rate constant and the reactant concentration raised to some powers, rate
law uses experimental values.
Rate law equation format: r=k[A]x[B]y
- r = Rate
- k = Rate constant
- [ ] = Concentration
- [A] & [B] = Concentration value of component A & B
- x & y = Reaction orders of given component
Reaction Orders (0 to 3)
Reaction orders are the values of x and y in the rate law equation, and expresses
the effect of the concentration change of a single reactant on the final
reaction rate.
Zero order:
- A0 = 1
- 20 = 1
- When concentration doubles, rate doesn’t change.
- Altering in concentrations does not affect overall reaction rate, as any
values to the power of zero equals one, therefore will not see a change in
result.
- Ex. [I-]0 does not need to be included in the rate law equation, as it
wouldn’t affect the final rate.
First order:
- A1 = 2
- 21 = 2
- Doubling in concentration lead to doubling in reaction rate.
Second order:
- A2 = 4
- 22 = 4
- Doubling in concentration leads to quadrupling in rate.
Third order:
- A3 = 8
- 23 = 8
, - Doubling in concentration leads to octuple in rate.
*Note: A will not always be 2, but whatever the concentration is going up
by to the power of whatever the change in rate is. See example below *
[F2] (M) [ClO2] (M) Initial Rate (M/s)
0.10 0.010 0.0012
0.10 0.040 0.0048
0.20 0.010 0.0024
Note that when calculating the reaction order for [ClO2], the rate value went
from 0.0012 to 0.0048 when the concentration quadrupled, meaning that the
change in concentration is equivalent to the change in rate.
Referring back to the previous orders law, we can see that when 2 is to the
power of 1, the rate equals 2, meaning that the concentration change and rate
change is equal to each other, defined as the first order.
Same idea applies to this example as well, when [ClO2] quadruples, the rate
quadruples as well, keeping the proportion of the reaction order rules, we can
see it as 41, or first order reaction.
Important: When calculating reaction orders for one component, ALWAYS
make sure that the concentration of the other component remains unchanged.
DO NOT use two trials with different values for both components.
Rate Law Calculations
Equation: r = k[A]x[B]y
When calculating for rate law, experimental values will always be given, and
the equation is usually manipulated/rearranged to solve for k.
Ex:
Trial # Intial [A] Initial [B] Initial Rate
1 1.00 M 1.00 M 1.25 × 10-2 M/s
2 1.00 M 2.00 M 2.50 × 10-2 M/s
3 2.00 M 2.00 M 2.50 × 10-2 M/s
Calculate for:
- Rate Law equation
