Efficiency of reversible reaction: a graphical approach

• Published in: Chemistry Teacher International : best practices in chemistry education 2022-10, Vol.4 (3), p.271-277
• Main Author: Novak, Igor
• Format: Article
• Language: English
• Subjects: advancement ratio of reaction; efficiency of reaction; equilibrium; extent of reaction; le chatelier’s principle
• ISSN: 2569-3263; 2569-3263
• DOI: 10.1515/cti-2022-0004

We describe simple, quantitative, graphical approach to solve chemical equilibrium problems and quantify how far the reversible reaction advances upon reaching equilibrium state at a given temperature. The same approach also gives the change in reaction advancement ratio (reaction efficiency; % completion of reaction) upon perturbation of equilibrium state by changing equilibrium concentrations (moles) of reactants or products. The approach is based on plotting two polynomial functions which represent how the numbers of moles of reactants and products vary with the advancement of reaction. The point of intersection of the two polynomial curves (functions) gives advancement ratio for a reversible reaction at equilibrium ( χ e ). In comparison, Le Chatelier’s principle is qualitative and tells us that equilibrium concentrations (moles) of products will increase (or decrease) once concentrations of reactants are made larger (or smaller), but does not predict the change in advancement of reversible reaction upon re-establishing the equilibrium state. In other words, it does not specify whether after perturbation the conversion to products will result in higher or lower reaction efficiency. Our quantitative approach is complementary to the qualitative Le Chatelier’s principle and is applicable to any single-equation equilibrium system. It can also be an alternative to ICE tables.