Laboratory 2 Procedure – Chemical Kinetics

Background:

During chemical reactions, reagents must collide with enough kinetic energy and proper orientation in order to form a product. Kinetic energy depends on the velocity of colliding molecules. Analyzing the factors that can affect velocity, the rate, of the reaction can help us control chemical processes. Study that describes the reaction rates, mechanisms, bond breaking and making processes during chemical reaction is called Chemical Kinetics.

In this experiment we will analyze reaction rate dependence on initial concentration of the reactant as well as the rate dependence the temperature.

A + BC →AC + B

Figure 1: Generic Single Displacement Reaction.

Average reaction rate for the reaction described in Figure 1 is as follows:

rate = -Δ[A] / Δt

Equation 1: Average Rate of the Reaction, where Δ[A] is the difference between final and initial concentrations of reagent A, and Δt is the final – initial measured time frame.

There are several objectives of this lab:

• To enhance your understanding of the meaning of the term ‘rate’ with respect to a chemical process.
• To improve your calculations of Δ[]/Δt based on the collected data.
• To understand concentration and temperature effects on the reaction rate.

Before you start this laboratory assignment, you are encouraged to review Section 13.1 on page 443 in the textbook. Throughout this laboratory assignment, you will be required to perform and thoroughly document your calculations pertaining to the average reaction rate associated with the reaction above. Be sure to record all observations and any relevant notes that you think you will need to include in your laboratory report.

Pre-Lab Questions:

1.What can affect a reaction rate? Explain your answer.

2.If a reaction is endothermic, and we increase the temperature of the reaction mixture, how will it affect the overall reaction rate?

Procedure:

Collecting Data and Performing the Experiment

From the course home page, access the simulation environment by clicking on the “Reactions & Rates” link. This will initiate a download of a Java file that you will need to open on your desktop. Note: If you do not have the proper Java version to run the file, check the “Materials” section of the course syllabus for more details on acquiring the software.

1.After the simulation environment loads, choose the “Rate Experiments” tab, and then set concentration of reagents: A for 10, and BC for 20. The black arrow below shows the location, where the changes should bemade.

• Mark “Show Stopwatch”, as shown below
• Repeat procedures 1-6 for the remaining concentrations in Table 1 and record your results in the appropriate cells.
• Record your data in Table 2.

:

3.Then mark “AB Molecule”.

4.At this point, we’re ready to begin the simulation. You will need to initiate the experiment by clicking “Begin Experiment” then immediately starting the stopwatch. After you start simulation, make sure that you stop it by clicking the stopwatch when the concentrations of products appear in the “Current Amounts box. Become familiar with starting and stopping the experiment and stopwatch several times before you are ready to make your first official measurement as this may take some coordination.

5.Record time in the Table 1 on the row with the corresponding concentrations used in the experiment. Ensure the accuracy of your results by running several trials.

7.To simulate effect of temperature on the reaction rate follow the procedures from steps 1-6 and each time adjust the temperature. Move the temperature slider to the right to a position so that the “Total Average Energy” line on the reaction coordinate moves upward only a small amount. Keep this temperature as you run trials for the concentrations listed in Table 2.

Data Analysis

9.Table 1. Initial concentrations of reagents and average reaction rate at constant temperature. COLDSETTINGS

10.Table 2. Initial concentrations of reagents and average reaction rate at constant temperature. HOTSETTINGS

Notes

This section should include notes about any observations or data collected during the lab.

Report Requirements

This section contains key information that must be included in your typed report.

• Define the problem in a manner that is clear and insightful.
• Identify the strategies and procedures used during the lab.
• Clear presentation of data including any tables or other figures that are relevant to understanding your stated conclusions at the end of the report. Include any relevant calculations performed during the lab.
• Conclusive statements arguing in favor of your findings.

3.Clear hypothesis statement and other potential solutions that identify any relevant contextual factors (i.e. real-world costs).

5.Clearly stated results and discussion of possible improvements to the procedure.

Note: All reports will be graded using the rubric embedded within the course.

Here are some questions to consider as you write your report:

1.Does my problem statement make sense?

1. Have I summarized my strategies/procedures well enough to be replicated by an outsider?
2. Did I have a valid hypothesis at the start of the lab? Have I expressed this in my report?
3. Do my tables and/or graphs make sense?
4. Are my conclusions valid based on my supplied data?

Did I thoroughly summarize my laboratory experience in a concise, factual way such that the reader can understand my processes and findings in the conclusion section

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