Page 378 - Chemistry eBook

How to Balance a Redox Reaction
Ca0 + Al+3 Ca+2 + Al0
1. Find the half reactions to see if there is an equal number of electrons in the two half reactions.
Oxidation (LEO right): Ca0 Ca+2 + 2e-
Reduction (GER left): Al+3 + 3e- Al0
Oxidation had 2 electrons and reduction has 3. Hey, it’s not even. Let’s balance this out.
2. Multiply each half reaction by the number of electrons in the other to make the number of electrons equal.
3 (Ca0 Ca+2 + 2e-) = 3Ca0 3Ca+2 + 6e- 2 (Al+3 + 3e- Al0) = 2Al+3 + 6e- 2Al0 Both sides have 6 electrons. They’re even now.
3. Now, go back to the original equation and insert the new coefficients.
3Ca0 + 2Al+3 3Ca+2 + 2Al0. This is the balanced equation!
At the end, double check to see that if the mass is balanced. If it’s not balanced, then balance it the usual way, as we did in unit 5.
377 © UNIT 10: OXIDATION & REDUCTION