In order to calculate a rate law you must first determine the rate of reaction. The rate of reaction is defined as the change in concentration of a reactant or product per unit time. In order to calculate the rate you must measure the concentration of a reactant or product at two different points in time and divide the change in concentration by the change in time. This will give you the rate of change for thereactant or product.
Once you have the rate of change for the reactant or product you can then determine the rate law. The rate law is an equation that relates the rate of reaction to the concentrations of the reactants. The rate law equation has the following form:
rate = k[A]^x[B]^y
In this equation k is the rate constant [A] and [B] are the concentrations of the reactants and x and y are the orders of reaction for reactant A and reactant B respectively. The order of reaction is defined as the power to which the concentration of a reactant is raised in the rate law equation. The order of reaction can be determined by conducting an experiment in which the concentration of one reactant is varied while the concentration of the other reactant is held constant. By doing this you can determine how the rate of reaction changes as the concentration of the reactant is increased. If the rate of reaction doubles when the concentration of the reactant is doubled then the order of reaction is 1. If the rate of reaction quadruples when the concentration of the reactant is doubled then the order of reaction is 2 and so on.
Once you have determined the orders of reaction for the reactants you can then plug in the values for the rate and the concentrations of the reactants into the rate law equation to solve for the value of the rate constant k.
The rate law equation can be used to predict the rate of reaction for different concentrations of reactants. For example if you know that the rate of reaction is doubled when the concentration of reactant A is doubled you can predict that the rate will be tripled if the concentration of reactant A is tripled. Similarly if you know that the rate of reaction is tripled when the concentration of reactant B is doubled you can predict that the rate will be quadrupled if the concentration of reactant B is tripled.
You can also use the rate law equation to determine the effect of a change in temperature on the rate of reaction. For example if the rate constant k is doubled when the temperature is increased by 10 degrees Celsius you can predict that the rate of reaction will be doubled if the temperature is increased by 20 degrees Celsius.
The rate law for the following reaction is second order with respect to A.
2A + B → products.
What is the unit for the rate constant?
Answer 1: The rate constant for this reaction is second order with respect to A so the unit is mol L-1 s-1.
The rate law for the following reaction is first order with respect to A.
2A + B → products.
What is the unit for the rate constant?
Answer 2: The rate constant for this reaction is first order with respect to A so the unit is s-1.
The rate law for the following reaction is zero order with respect to A.
2A + B → products.
What is the unit for the rate constant?
Answer 3: The rate constant for this reaction is zero order with respect to A so the unit is L mol-1 s-1.
The rate law for the following reaction is first order with respect to A and B.
2A + B → products.
What is the unit for the rate constant?
Answer 4: The rate constant for this reaction is first order with respect to A and B so the unit is L mol-1 s-1.
The rate law for the following reaction is second order with respect to A and first order with respect to B.
2A + B → products.
What is the unit for the rate constant?
Answer 5: The rate constant for this reaction is second order with respect to A and first order with respect to B so the unit is L mol-1 s-1.
The rate law for the following reaction is zero order with respect to A and second order with respect to B.
2A + B → products.
What is the unit for the rate constant?
Answer 6: The rate constant for this reaction is zero order with respect to A and second order with respect to B so the unit is mol-1 L s-1.
The rate law for the following reaction is zero order with respect to A and first order with respect to B.
2A + B → products.
What is the unit for the rate constant?
Answer 7: The rate constant for this reaction is zero order with respect to A and first order with respect to B so the unit is L s-1.
The rate law for the following reaction is first order with respect to A and zero order with respect to B.
2A + B → products.
What is the unit for the rate constant?
Answer 8: The rate constant for this reaction is first order with respect to A and zero order with respect to B so the unit is s-1.
The rate law for the following reaction is second order with respect to A and zero order with respect to B.
2A + B → products.
What is the unit for the rate constant?
Answer 9: The rate constant for this reaction is second order with respect to A and zero order with respect to B so the unit is L mol-1 s-1.
The rate law for the following reaction is second order with respect to A and first order with respect to B.
2A + B → products.
What is the unit for the rate constant?
Answer 10: The rate constant for this reaction is second order with respect to A and first order with respect to B so the unit is L mol-1 s-1.
The rate law for the following reaction is zero order with respect to A and second order with respect to B.
2A + B → products.
What is the unit for the rate constant?
Answer 11: The rate constant for this reaction is zero order with respect to A and second order with respect to B so the unit is mol-1 L s-1.
The rate law for the following reaction is zero order with respect to A and first order with respect to B.
2A + B → products.
What is the unit for the rate constant?
Answer 12: The rate constant for this reaction is zero order with respect to A and first order with respect to B so the unit is L s-1.
The rate law for the following reaction is first order with respect to A and zero order with respect to B.
2A + B → products.
What is the unit for the rate constant?
Answer 13: The rate constant for this reaction is first order with respect to A and zero order with respect to B so the unit is s-1.
The rate law for the following reaction is second order with respect to A and zero order with respect to B.
2A + B → products.
What is the unit for the rate constant?
Answer 14: The rate constant for this reaction is second order with respect to A and zero order with respect to B so the unit is L mol-1 s-1.
The rate law for the following reaction is second order with respect to A and first order with respect to B.
2A + B → products.
What is the unit for the rate constant?
Answer 15: The rate constant for this reaction is second order with respect to A and first order with respect to B so the unit is L mol-1 s-1.
