Reaction Stoichiometry
Reaction stoichiometry problems are introduced by the middle of the first term
of most introductory chemistry courses - often well before many students have
fully understood some of the basics of chemistry problem solving, and of mole
conversion problems in particular. Consider the possible errors that the
student might make in solving this rather simple reaction stoichiometry problem.
How much of an excess fuel is there in a rocket containing 25 kilograms of
oxygen and hydrogen in each of the respective two fuel tanks?
Before starting, consider what tools you will need to solve this problem. I
will assume all of you have some paper, pencil, a standard calculator, and
perhaps a periodic table. We will open the Reaction Mode, which is set up like a spreadsheet. 
Using the popup periodic table and numeric keypad, we will "write" the chemical formulas of the reactants and product. For the
sake of completeness, let us check on the equation balance by clicking on the Check button. 
(The balance "check" results in a display of the "constituent" formulas of
the reactants and products.) The equation can now be balanced by clicking the Balance button. 
To test the amount of oxygen required to react with 25 kilograms of hydrogen,
we would enter in the amount in the "mass" cell. 
The amount of reactants and products required and produced are calculated
when you click on the Evaluate button. 
We can repeat this calculation for 25 kilograms of oxygen:
Types of Errors introduced in reaction stoichiometric calculations:
Consider the types of errors that might be made to complete this calculation:
- Chemical formula errors: You must know and write the correct chemical formulas of the reactants and
products.
- Molar Mass calculation errors: You must calculate the correct molar masses of the reactants and products.
- Balancing an equation: You must obtain a balanced equation.
- Stoichiometric calculation errors: If you have not determined the limiting reagent, you must go through two sets
of [mass
mole mole mass] calculations.
(Comment: I remember encountering college senior-level chemistry students who
were still having trouble with solving limiting reagent problems.)
Like to try another problem? Return to Sample Problems.