Balancing Abstract Chemical Equations
This Demonstration solves chemical-like equations. Atoms are represented by letters A, B, C, etc. An expression like can be thought of as a "molecule" in which atoms are joined to a atom and atoms. For the equation to be balanced, the atom counts on both sides must be the same.
 D. E. Goldberg, Schaum's 3000 Solved Problems in Chemistry, New York: McGraw-Hill, New York, 1988 pp. 151–164.