Introduction to Chemical Kinetics
Chemical kinetics is the study of the rates of chemical reactions and the mechanisms by which they occur. It is a branch of physical chemistry.
Key Points
- Chemical kinetics is concerned with the rates of chemical reactions and the mechanisms by which they occur.
- The rate of a chemical reaction is the change in concentration of reactants or products over time.
- The rate law for a chemical reaction is an equation that expresses the relationship between the rate of the reaction and the concentrations of the reactants.
- The rate constant for a chemical reaction is a proportionality constant that appears in the rate law.
- The order of a chemical reaction is the sum of the exponents of the concentrations of the reactants in the rate law.
- The molecularity of a chemical reaction is the number of molecules that collide in a single elementary reaction.
- The collision theory of chemical kinetics is a model that explains how chemical reactions occur.
- The transition state theory of chemical kinetics is a model that explains how chemical reactions occur by forming a high-energy intermediate called the transition state.
Main Concepts
Rate of a Chemical Reaction: The rate of a chemical reaction is the change in concentration of reactants or products over time. It can be measured by monitoring the concentration of one or more reactants or products as a function of time.
Rate Law: The rate law for a chemical reaction is an equation that expresses the relationship between the rate of the reaction and the concentrations of the reactants. The rate law is determined experimentally.
Rate Constant: The rate constant for a chemical reaction is a proportionality constant that appears in the rate law. The rate constant depends on the temperature and the nature of the reactants.
Order of a Chemical Reaction: The order of a chemical reaction is the sum of the exponents of the concentrations of the reactants in the rate law. The order of a reaction can be determined from the rate law.
Molecularity of a Chemical Reaction: The molecularity of a chemical reaction is the number of molecules that collide in a single elementary reaction. The molecularity of a reaction can be determined from the stoichiometry of the reaction.
Collision Theory of Chemical Kinetics: The collision theory of chemical kinetics is a model that explains how chemical reactions occur. According to the collision theory, chemical reactions occur when reactants collide with each other with enough energy and in the correct orientation to form products.
Transition State Theory of Chemical Kinetics: The transition state theory of chemical kinetics is a model that explains how chemical reactions occur by forming a high-energy intermediate called the transition state. According to the transition state theory, the transition state is a high-energy intermediate that forms when reactants collide with each other. The transition state then decomposes to form products.
Experiment: Introduction to Chemical Kinetics
Objective:
To investigate the factors that affect the rate of a chemical reaction.
Materials:
- Sodium thiosulfate solution (0.1 M)
- Hydrochloric acid solution (0.1 M)
- Potassium iodide solution (0.1 M)
- Starch solution (0.1% w/v)
- 10-mL pipette
- 100-mL beaker
- Stopwatch
- Safety goggles
Procedure:
- Put on safety goggles.
- Measure 10 mL of sodium thiosulfate solution into a 100-mL beaker.
- Add 10 mL of hydrochloric acid solution to the beaker.
- Swirl the beaker to mix the solutions.
- Immediately add 10 mL of potassium iodide solution to the beaker.
- Swirl the beaker to mix the solutions.
- Start the stopwatch.
- Observe the reaction mixture. The solution will turn cloudy as a precipitate of silver iodide forms.
- Stop the stopwatch when the solution becomes completely cloudy.
- Record the time it took for the reaction to complete.
- Repeat steps 2-10 using different concentrations of sodium thiosulfate and hydrochloric acid solutions.
Data:
Concentration of Sodium Thiosulfate (M) |
Concentration of Hydrochloric Acid (M) |
Time for Reaction to Complete (s) |
|---|
0.1 |
0.1 |
10 |
0.2 |
0.1 |
5 |
0.1 |
0.2 |
20 |
Results:
The rate of the reaction increased as the concentration of sodium thiosulfate increased. The rate of the reaction also increased as the concentration of hydrochloric acid increased. This is consistent with the following rate law:
Rate = k[Na2S2O3][HCl]
where k is the rate constant.
Discussion:
The rate of a chemical reaction is affected by a number of factors, including the concentration of the reactants, the temperature, and the presence of a catalyst. In this experiment, we investigated the effect of the concentration of the reactants on the rate of the reaction. The results of the experiment show that the rate of the reaction increased as the concentration of the reactants increased. This is because the more reactants there are, the more likely they are to collide with each other and react.
The rate of a chemical reaction can also be affected by the temperature. In general, the rate of a reaction increases as the temperature increases. This is because the higher the temperature, the more energy the reactants have, and the more likely they are to overcome the activation energy barrier and react.
The presence of a catalyst can also affect the rate of a chemical reaction. A catalyst is a substance that speeds up the rate of a reaction without being consumed in the reaction. Catalysts work by providing an alternative pathway for the reaction to take place, which lowers the activation energy barrier and makes it more likely for the reactants to react.
Conclusion:
In this experiment, we investigated the factors that affect the rate of a chemical reaction. The results of the experiment show that the rate of the reaction increased as the concentration of the reactants increased. This is consistent with the rate law for the reaction. The rate of the reaction can also be affected by the temperature and the presence of a catalyst.
