The following pictures represent the progress of a reaction in which two A molecules combine to give a more complex molecule A2, 2 AS A2.
(b) What is the rate law?

Verified step by step guidance

1. Step 1: Identify the reaction given: 2A -> A2.
2. Step 2: Observe the images provided, noting the number of A molecules at each time interval (0 min, 1 min, 2 min).
3. Step 3: Determine the change in concentration of A molecules over time by counting the number of A molecules at each time interval.
4. Step 4: Use the rate law expression for a reaction of the form 2A -> A2, which is rate = k[A]^2, where k is the rate constant.
5. Step 5: Conclude that the rate law for this reaction is rate = k[A]^2, indicating a second-order reaction with respect to A.

Key Concepts

Rate Law

The rate law is an equation that relates the rate of a chemical reaction to the concentration of its reactants. It is typically expressed in the form rate = k[A]^m[B]^n, where k is the rate constant, and m and n are the orders of the reaction with respect to reactants A and B, respectively. Understanding the rate law is crucial for predicting how changes in concentration affect the reaction rate.

Reaction Order

Reaction order refers to the power to which the concentration of a reactant is raised in the rate law. It indicates how the rate of reaction is affected by the concentration of that reactant. For example, a first-order reaction means that the rate is directly proportional to the concentration of one reactant, while a second-order reaction indicates that the rate is proportional to the square of the concentration of that reactant.

Molecularity

Molecularity is the number of reactant molecules involved in an elementary reaction step. It can be unimolecular (one molecule), bimolecular (two molecules), or termolecular (three molecules). In the context of the given reaction, where two A molecules combine to form A2, the reaction is bimolecular, which is important for determining the rate law and understanding the mechanism of the reaction.