Order of Reaction
Explains the power to which the concentration term is raised in the rate law, defining individual and overall reaction orders, and methods for their determination.
What is Order of Reaction?
The sum of the exponents of the concentration terms in the experimentally determined rate law equation for a chemical reaction.
Key formula / rule: General Rate Law
Key points
- Define the order of a reaction with respect to a reactant.
- Determine the overall order of a reaction.
- Explain the difference between order of reaction and molecularity.
- Identify that the order of reaction is an experimental quantity.
Common exam trap
Assuming reaction order from the balanced chemical equation's stoichiometry.
Definitions
- Term
Order of Reaction
- Meaning
The sum of the exponents of the concentration terms in the experimentally determined rate law equation for a chemical reaction.
- Term
Individual Order
- Meaning
The exponent of the concentration of a specific reactant in the rate law.
- Term
Overall Order
- Meaning
The sum of the individual orders of all reactants in the rate law.
- Term
Zero Order Reaction
- Meaning
A reaction whose rate is independent of the concentration of any reactant.
Learning objectives
Define the order of a reaction with respect to a reactant.
Determine the overall order of a reaction.
Explain the difference between order of reaction and molecularity.
Identify that the order of reaction is an experimental quantity.
Understand the concept of a zero-order reaction.
Formulae
- Name
General Rate Law
- Note
x and y are orders with respect to A and B; x+y is the overall order.
- Expression
Rate = k[A]x[B]y
- Name
Zero Order Reaction Rate
- Note
Rate is independent of reactant concentrations.
- Expression
Rate = k
Prerequisites
Chemical Kinetics
Rate of Reaction
Rate Law
Concentration of Reactants
Common mistakes
Assuming reaction order from the balanced chemical equation's stoichiometry.
Confusing order of reaction with molecularity.
Incorrectly calculating overall order by summing up incorrect individual orders.
Keywords
Order of Reaction
Rate Law
Rate Constant
Concentration Dependence
Experimental Order
Overall Order
Zero Order
Practice preview
What does the 'order of a reaction' represent in chemical kinetics?…
easy
For a zero-order reaction, how does the rate of reaction change with respect to the concentration of reactants?…
easy
Consider the reaction: 2NO(g) + O2(g) → 2NO2(g). If the rate law is experimentally determined to be Rate = k[NO]^2[O2]^1, what is the order with respect to NO and O2, respectively?…
medium