CROSS MULTIPLICATION
We already looked at how the ozone equation could be balanced using
fractions. There is another way to balance the equation and it is the
preferred way when it can be used because it avoids fractions. Remember
that we had:
O3 => O2
A simple way to balance this equation is to cross multiply. We
multiple O3 by 2 and multiple O2 by 3. Thus we have:
2 O3 => 3 O2
You can see that we have 6 oxygen atoms on each side.
Now lets look at a more complex example using Chem Spread.
A copy of the calculator is provided below for this exercise.
1. Hit UNDO until formula entry window is clear.
2. Enter #K? and hit SUBMIT
3. This should give the equation: KClO3 => KCl + O2
4. Enter your guess for coefficients for KClO3 and O2 to balance O.
We want to cross multiply the element O. To type in a coefficient,
click on the formula entry window and move the cursor with the arrow
keys until it is where you want to type the coefficient. Type in
two coefficients for this example.
5. Hit SUBMIT and see if oxygen balances. If you don't have 6
O's on each side, go back and try step 4 again.
6. Now choose a coefficient for KCl so K is balanced and hit SUBMIT
7. Congratulations, you balanced your first complex equation.
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