A New Approach to Stoichiometric Problem Solving

It is proposed that stoichiometric problem solving be based on changes of measured physical quantities such as masses, chemical amounts, numbers of molecules, etc. of reactants or products and that the notation be adjusted accordingly: the changes should be denoted by the difference operator Delta as is usual in the field of thermodynamics. Instead of using ratios of masses, amounts, etc. it is better to use ratios of changes in the corresponding quantities. This leads to the appearance of negative values which are automatically compensated by the accepted definition of stoichiometric numbers. All these changes are mutually related via the extent of reaction and introductory chemistry courses for chemists and related fields should not avoid the concept of extent of reaction. This quantity is, as a "quantity of state" of advancement of the chemical process, essential for the understanding of chemical thermodynamics and chemical kinetics, but it also shows certain advantages in solving more complicated stoichiometric problems.