Physical chemistry is a challenging course and it can be easy for students to become overly focused on the details of the subject such that they lose sight of the broader applications of the discipline. Bomb calorimetry is a commonly used experiment in introductory physical chemistry courses as an example of thermodynamic state functions (Δ<i>U</i> and Δ<i>H</i>). Frequently the primary application of this technique is to measure the energy content in commercial food items (candy, chips, etc.). To highlight some alternative thought provoking applications of this experimental technique, we have designed two experiments that use bomb calorimetry data to encourage a discussion on the environmental issues of plastic waste/recycling and ethanol as a fuel additive or an alternative to gasoline. In the first experiment, students combust samples of different recycling coded plastics to determine the energy content of the different types. Based on these collected energy values as well as comparisons to the energy content of fossil fuels, students can have discussions on whether plastics are a reasonable source of combustible energy and what characteristics make certain plastics a better fuel source for waste energy plants. The second experiment uses a liquid combustion technique to measure the combustion energy of ethanol, pure gasoline, and a number of blended mixtures to create a calibration curve of internal combustion energy vs. ethanol concentration. Students can then use the curve to identify the concentration of ethanol in fuel sample from a local gas station, analyze the energy change of increasing the ethanol concentration of the fuel mixture, and compare their calibration curve to a combustion efficiency curve for the same mixtures to explore the differences in expansion when combusting ethanol versus gasoline. In both cases, bomb calorimetry becomes a tool to investigate an environmental question giving students a fresh application of their thermodynamic studies.

Connecting bomb calorimetry to environmental issues: Two applied bomb calorimetry experiments

ACS Fall 2021

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