April 2019 Limerick Project

Balancing Reactions

“To balance a given reaction,
Complete an established transaction.
‘Cross the arrow you must
Coefficients adjust:
Conserve mass and ensure satisfaction.”

Many of the April 2019 limericks were written with a potential teaching objective in mind, and the April 3 limerick is one of them.  As I’ve taught the same topics more often, I’ve started to hear more of a rhythm and rhyme when I do so.  

“To balance a given reaction,/
Complete an established transaction.”  
I have had occasion to collaborate with generous teaching colleagues outside of chemistry in the past decade, and thus to benefit from their expertise while hearing their external perspectives on my discipline.  One of the most interesting themes we’ve discussed is that, for non-specialists, learning to “balance reactions” is often one of the most vivid memories of their high school chemistry courses. Balancing a reaction means confirming that the reaction has equal numbers of elements as reactants (on the left side of the reaction arrow) and products (on the right side).

In building on this conversation, it has been illustrative to contrast the skills of chemistry with the discipline of chemistry itself.  In my experience, it’s rare that someone enjoys learning the concrete skill of balancing reactions, but mastering that skill opens the door to many interesting disciplinary applications. The introductory experience is similar to learning piano scales: the skill can open many wonderful doors, but the skill itself (at least for this once-aspiring pianist!) isn’t necessarily the fun part.       

“‘Cross the arrow you must/ Coefficients adjust:/
Conserve mass and ensure satisfaction.”  

Chief among the rules in balancing reaction equations: the only numbers that can change to achieve said balance are the numbers in front of each chemical formula– the coefficients– rather than the subscripts on the chemical formulas themselves.  (Changing the subscripts changes the identity of the chemical species.) 

Further, it’s easy to overlook as one is mastering the skill, but a balanced reaction is an elegant contextualization of the law of conservation of mass; a chemical reaction does not create or destroy matter: it simply rearranges it.