Kinetics of Herbicide Photodegradation

Kristi Closser, California State University-Fresno, Chemistry
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This lab activity is designed to connect student's knowledge of reaction rates to actual data and an unfamiliar system (photodegradation of phenylurea herbicides in the presence of various catalysts). Students use MATLAB to plot and interpret the data.

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Learning Goals

By completing this activity, students will

  • Analyze experimental data to determine the order of the reaction
  • Use MATLAB to create plots of experiential data

Context for Use

Designed for an upper division undergraduate course in physical chemistry with 20-30 students.

This activity is planned for a two hour computer lab session after 1-2 lecture periods on chemical kinetics, and students are expected to have minimal experience using MATLAB.

Required MATLAB skills
  • loading data from .mat file
  • basic manipulation and 2D plotting of data
Required subject skills
  • knowledge of basic chemical kinetics
  • familiar with determining the order of reaction from a plot

Description and Teaching Materials

Phenylurea compounds are a class of molecules that are widely used as herbicides for weed control in both agricultural and non-agricultural settings. This activity has students analyze published experimental data to determine the kinetics of their photodegradation.

Students use a MATLAB live script to work through the analysis of the data.

MATLAB student template: phenylurea_template.mlx (MATLAB Live Script 47kB Oct9 19)

MATLAB data file (.mat): phenylurea_data.mat (Matlab .MAT File 4kB Oct8 19)

Teaching Notes and Tips

This activity is designed for students who have minimal exposure to MATLAB. They should have skills equivalent to completing the MATLAB Onramp, but the livescript template guides them through the steps.

To increase difficulty, instructors could not use the template or have students extract the data from the paper.


Students submit their MATLAB live scripts through course management system.

They are also asked to explain the kinetic concepts during the lecture portion of the course.

Solutions for the instructor are provided: phenylurea_instructor_key.mlx (MATLAB Live Script 429kB Oct9 19)

References and Resources

Brief overview of chemical kinetics:

Paper for kinetics data: Fenoll, J.; Sabater, P.; Navarro, G.; Perez-Lucas, G.; Navarro, S.; "Photocatalytic transformation of sixteen substituted phenylurea herbicides in aqueous semiconductor suspensions: Intermediates and degradation pathways" Journal of Hazardous Materials, v. 244-245 (2013) p. 370-379.