A photochromic reaction to design original laboratory sessions for studying kinetics and uncertainties.
Abstract
Original laboratory sessions based on the thermal back-reaction of a photochromic compound (6-NO2 BIPS) can be implemented for students at the preparatory-class/undergraduate level to introduce key concepts in chemical kinetics. Time-dependent monitoring can be performed using UV–Visible absorption spectroscopy, as well as IR spectroscopy or spectrofluorimetry. Data analysis using both differential and integral methods enables determination of the reaction order p, the rate constant k, and their uncertainties. A UV-Visible spectrophotometrybased version of the experiment was tested with 60 students enrolled in a first-year PCSI preparatory class (including pre-lab work). Since the process is reversible, with no photodegradation of the compound, and the reaction in ethyl acetate is fast (t1/2 ≈ 22 s at 25 °C), each student pair can perform several successive measurements, calculate mean values and standard deviations for p and k, and compare their results with literature values using a zeta-score. Over two 2-hour laboratory sessions, 30 student pairs generated a total of 124 absorbance-decay curves. A detailed experimental protocol and a ready-to-use laboratory worksheet are provided for a 2-hour teaching session. A dataset is also made available to allow comprehensive statistical analysis.
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BibTeX
@article{clede2026photochromic,
title = {{A photochromic reaction to design original laboratory sessions for studying kinetics and uncertainties.}},
author = {Sylvain Clède and Jonathan Piard},
journal = {L'Actualité Chimique},
year = {2026},
month = sep,
doi = {10.63133/scf.act-},
url = {https://hal.science/hal-05756241v1},
note = {CC BY-NC-SA 4.0},
}
RIS
TY - JOUR
TI - A photochromic reaction to design original laboratory sessions for studying kinetics and uncertainties.
AU - Sylvain Clède
AU - Jonathan Piard
PY - 2026
DA - 2026/09/20
JO - L'Actualité Chimique
DO - 10.63133/scf.act-
UR - https://hal.science/hal-05756241v1
AB - Original laboratory sessions based on the thermal back-reaction of a photochromic compound (6-NO2 BIPS) can be implemented for students at the preparatory-class/undergraduate level to introduce key concepts in chemical kinetics. Time-dependent monitoring can be performed using UV–Visible absorption spectroscopy, as well as IR spectroscopy or spectrofluorimetry. Data analysis using both differential and integral methods enables determination of the reaction order p, the rate constant k, and their uncertainties. A UV-Visible spectrophotometrybased version of the experiment was tested with 60 students enrolled in a first-year PCSI preparatory class (including pre-lab work). Since the process is reversible, with no photodegradation of the compound, and the reaction in ethyl acetate is fast (t1/2 ≈ 22 s at 25 °C), each student pair can perform several successive measurements, calculate mean values and standard deviations for p and k, and compare their results with literature values using a zeta-score. Over two 2-hour laboratory sessions, 30 student pairs generated a total of 124 absorbance-decay curves. A detailed experimental protocol and a ready-to-use laboratory worksheet are provided for a 2-hour teaching session. A dataset is also made available to allow comprehensive statistical analysis.
SN - 0151-9093
SN - 2105-2409
ER -