So far the reactions we have looked at in detail have been of the metathesis type,
in which the first names and last names of the two reactants are simply exchanged.
However, some of the reactions we have discussed have not been of this type,
C(s) + O2(g) -----> CO2(g)
C6H12O6(aq) -----> 2 C2H5OH(aq) + 2 CO2(g)
These kinds of reactions are, in general, more complicated than the simple metathesis reactions. A discussion of these reactions is necessary before we can discuss the production of metals and explosives. The following method of balancing reactions will work for metathesis reactions as well as redox reactions.
The following procedure is guaranteed to produce an accurately balanced reaction equation for any electron-transfer (redox) equation that occurs in aqueous solution. In fact, it will even work for reaction equations in which no redox occurs, but then it's pretty tedious compared to balancing by inspection. The only thing you have to know to begin is the chemical identity of the major reactants and products of the reaction. Let's take the following example: a popular WWII German rocket propellant was nitric acid (HNO3) and hydrazine (N2H4).
SHORT SUMMARY: Separate reaction into unusual-element half-reactions, balance each half-reaction with respect to: (1) unusual element, (2) O using H2O, (3) H using H+, (4) charge using e-. Make e- donated equal e- accepted, and combine with appropriate cancellation.
In balancing these reactions you will always be given the reactants and products. The balanced equation cannot contain anything that was not in the skeleton reaction except that water, H+, and OH- may be introduced as needed.
In every redox reaction there is an oxidation and a reduction. They are opposite sides of the same coin. The half reaction with electrons on the right is the oxidation. The half reaction with electrons on the left is the reduction. Just as an insurance agent causes others to have insurance, an oxidizing agent causes the other reactant to be oxidized and is itself reduced. A reducing agent causes the other reactant to be reduced and it itself oxidized.
In the example above, N2H4 loses electrons in its half reaction. It is thus oxidized. Remember LEO: Lose Electrons Oxidation. Since it is oxidized, it is the reducing agent. HNO3 gains electrons in its half reaction and is reduced. LEO the lion says GER: Gain Electrons Reduction. Since it is reduced, HNO3 is the oxidizing agent.
This was a hard example designed to show most of the complications that might arise. Try your hand at balancing these simple equations. Do them the long way for practice. In each case, circle the oxidizing agent.
C2H5OH + O2 -----> CO2
PbS + O2 -----> SO2 + PbO
PbO + C -----> CO2 + Pb
Once you are comfortable with the simple problems, try this more complicated one which is about the same difficulty as the quiz problems.
KClO3 + C12H22O11 -----> KCl + CO2
This project is passed by quiz alone. It will consist of a single redox skeleton reaction for you to balance.
When you are ready to pass this project, I will give you the names of reactants and products for a redox reaction. You will balance it. If it is correct, you pass, if not, you fail but can try again (once per day) until you pass.