Chemical Kinetics

Step 1: Understanding the rate law.
The rate law is given by: The order of the reaction is the sum of the exponents of the concentration terms in the rate law. In this case:
- The exponent for is ,
- The exponent for is .

Step 2: Calculate the total order.
The total order is:

Step 3: Conclusion.
The order of the reaction is , which corresponds to option (2).

Step 1: Difference between Molecularity and Order of Reaction.
1. Molecularity of reaction refers to the number of reacting species (atoms, molecules, or ions) involved in a single step of a reaction. It is always a whole number and can only be determined from the reaction mechanism. Order of reaction, on the other hand, refers to the power to which the concentration of a reactant is raised in the rate law equation. It is an empirical value that may not necessarily be a whole number. 2. Molecularity is defined for elementary reactions, i.e., a single-step reaction, while Order of reaction is determined experimentally and can apply to both elementary and complex reactions.

Step 2: Conclusion.
Thus, molecularity is associated with the reaction mechanism, and order is determined from experimental data.

Step 1: Difference between Rate of Reaction and Rate Constant.
1. Rate of reaction is the change in concentration of a reactant or product per unit time during a chemical reaction. It is expressed in terms of concentration/time (e.g., mol/L·s).
Rate constant (k) is a proportionality constant in the rate law equation that relates the rate of reaction to the concentration of reactants. It depends on temperature and the nature of the reaction but is independent of concentration.
2. Rate of reaction varies with the concentration of the reactants and temperature, while Rate constant is constant at a given temperature for a specific reaction and does not change with the concentration of reactants.

Step 2: Conclusion.
The rate of reaction is variable and depends on conditions, while the rate constant is a fixed value at a given temperature for a specific reaction.

Step 1: Rate constant units.
For a zero-order reaction, the rate law is , where the rate constant has the unit of .

Step 2: Conclusion.
Thus, the unit of the rate constant for a zero-order reaction is .

Step 1: Unit of rate constant for first order reaction.
For a first order reaction, the rate law is: where is the rate constant and is the concentration of the reactant. The unit of rate is mol/L·s, and the unit of concentration is mol/L. Thus, the unit of for a first-order reaction is:

Step 2: Unit of rate constant for second order reaction.
For a second order reaction, the rate law is: where is the rate constant and is the concentration of the reactant. The unit of rate is mol/L·s, and the unit of concentration is mol/L. Thus, the unit of for a second-order reaction is:

Step 3: Conclusion.
Thus, the unit of rate constant for a first-order reaction is , and for a second-order reaction, it is .

Step 1: Rate Determining Step.
The rate determining step (RDS) is the slowest step in a reaction mechanism. It controls the overall rate of the reaction because the other steps occur much faster and do not limit the overall reaction rate.

Step 2: Order of Reaction.
The order of reaction refers to the power to which the concentration of a reactant is raised in the rate law. It is determined experimentally and may not necessarily be a whole number. The order of reaction gives us information about the relationship between the concentration of reactants and the rate of the reaction.

Step 3: Conclusion.
Thus, the rate determining step is the slowest step in a reaction, while the order of reaction describes the dependence of the rate on the concentration of reactants.