In a Year 13 Chemistry lesson this week, led by the Head of Chemistry Mr Mahesh Warrier, the abstract concept of equilibrium was brought to life through a classic experiment: determining the equilibrium constant (Keq) for the esterification of ethanoic acid and ethanol.
The goal was to investigate the reaction: CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O. The students aimed to prove that, unlike reactions that go to completion, this process reaches a dynamic balance where all four species coexist, and that Kc is indeed constant for a given temperature.
Working in groups, students carefully mixed precise volumes of 1.0 mol dm⁻³ ethanoic acid and ethanol with a concentrated sulfuric acid catalyst in a sealed boiling tube. This closed system was crucial to prevent the escape of volatile reactants or products. The flask was then placed aside for one week, allowing the mixture to reach equilibrium.
After this period, the students titrated aliquots of the equilibrium mixture against a standard sodium hydroxide solution. By measuring the concentration of unreacted ethanoic acid, students could work backwards. Using the reaction’s stoichiometry (a 1:1:1:1 ratio), students calculated the equilibrium concentrations of ethanol, ethyl ethanoate, and water.
Finally, students substituted these values into the equilibrium expression: Kc = [CH₃COOC₂H₅][H₂O] / [CH₃COOH][C₂H₅OH]. Comparing our calculated Kc values across the class revealed a satisfying consistency, typically around 4. This confirmed the fundamental principle that for a given reaction at a fixed temperature, the equilibrium constant is indeed a fixed value.
This hands-on investigation solidified our understanding of dynamic equilibrium and provided a tangible method for quantifying a reaction’s position, perfectly bridging the gap between textbook theory and practical chemistry.
Mr Mahesh Warrier
Head of Chemistry