Reactive Material Balances: Summary

The answers to the ConcepTests are given below and will open in a separate window. 
ConcepTest 2 Answer – This ConcepTest is an interactive screencast. Click on the information “i” in the top right corner of the screencast to select an answer.
Key points from this module:
  • Reactive material balances can be carried out using molecular species balances, extents of reaction, or atomic species balances.
  • When multiple reactions occur, each reaction has its own extent of reaction.
  • When calculating degrees of freedom, a common constraint is that the ratio of species does not change with extent of reaction. For example, products may form in a 2:1 ratio, and if those products are not involved in other reactions, then the ratio is always two and this decreases the degrees of freedom.
  • Stoichiometric coefficients are positive for products and negative for reactants.
From studying this module, you should now be able to:
  • Calculate degrees of freedom for material balances of multiple reactions.
  • Use extents of reaction to calculate the amounts of products and reactants when multiple reactions take place.
  • Solve reactive material balance problems for multiple reactions using:
    • molecular species balances
    • extent of reaction
    • atomic species balances¬†


Prepared by John L. Falconer, Department of Chemical and Biological Engineering, University of Colorado Boulder