GIVEREF
Rate Laws and Order of Reaction
A topic from the subject of Kinetics in Chemistry.
Rate Laws and Order of Reaction
IntroductionRate law is an equation that expresses the relationship between the rate of a chemical reaction and the concentrations of the reactants. Order of reaction is the power to which the concentration of a reactant is raised in the rate law.
Key Points
- Rate law: r = k[A]^a[B]^b, where r is the rate, k is the rate constant, [A] and [B] are the concentrations of the reactants, and a and b are the orders of reaction with respect to A and B, respectively.
- Order of reaction: The order of reaction with respect to a reactant tells us the number of molecules of that reactant that must collide simultaneously to produce a reaction.
- Determining order of reaction: The order of reaction is determined experimentally by measuring the rate of reaction at different reactant concentrations.
- Zero-order reaction: A reaction that does not depend on the concentration of any of its reactants.
- First-order reaction: A reaction that depends on the concentration of one of its reactants linearly.
- Second-order reaction: A reaction that depends on the concentration of one of its reactants squared.
- Third-order reaction: A reaction that depends on the concentration of one of its reactants cubed.
Main Concepts
- Rate of reaction: The rate of a reaction is the change in concentration of a reactant or product per unit time.
- Rate constant: The rate constant is a proportionality constant that depends on the temperature and other factors that affect the reaction.
- Reaction mechanism: The reaction mechanism is a step-by-step description of the molecular events that lead to the formation of products from reactants.
- Activation energy: The activation energy is the minimum amount of energy that must be supplied to the reactants in order for the reaction to occur.
Experiment: Rate Laws and Order of Reaction
Objective: To determine the rate law and order of a chemical reaction.
Materials:
- Two beakers
- Stopwatch
- Pipettes
- Reagents (e.g., sodium thiosulfate, iodine, sulfuric acid)
Procedure:
- Prepare two solutions, one containing sodium thiosulfate and the other containing iodine.
- Pipette known volumes of each solution into the beakers.
- Start the stopwatch and add a few drops of sulfuric acid to one beaker.
- Swirl the beaker gently and observe the reaction.
- Stop the stopwatch when the reaction is complete (e.g., the solution turns colorless).
- Repeat steps 2-5 for different volumes of the reactants.
Key Procedures:
- Use astopwatch to accurately measure reaction time.
- Keep the temperature constant throughout the experiment.
- Vary the initial concentrations of the reactants systematically.
Significance:
This experiment allows students to observe and analyze the effects of initial reactant concentrations on reaction rate.
From the data obtained, students can determine the rate law and order of the reaction, which provide valuable information about the reaction mechanism.
This experiment helps students understand the fundamental principles of chemical kinetics and how reaction rates can be influenced by various factors.