AP Chemistry : Balancing Equations
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Example Question #11 : Balancing Equations
Transesterification is an industrially important process for the production of biodiesel fuel (that most diesel engines can run cleanly on) and glycerin from triglycerides (usually people use vegetable oil as their feedstock).
One easy to do and high yielding method involves the reaction of ethanol or methanol with sodium hydroxide to produce the super bases sodium ethoxide or sodium methoxide respectively. The super base is then used in the transesterification reaction with triglycerides to produce glycerin and ethyl or methyl esters (biodiesel). The products can easily be separated by differences in density. Note: For this reaction to occur the reactants must be free of water as when water is present saponification occurs (how soap is made) which will compete with the transesterification reaction. Note: just because the reaction described above is easy doesn't mean that it is anywhere near safe; please do thoroughly research any reaction you plan to undertake and take all possible safety precautions. That being said, this process is becoming much more popular lately and with the recent focus on alternative energy may well soon account for a decent portion of fuel production.
Catalyst formation equation:
Unbalanced transesterification equation:
Balance the following transesterification reaction assuming that all R-groups are identical:
The steps for balancing equations are as follows and should be done in order:
1.) Check for diatomic molecules: In this case there are none so move on to step 2
2.) Balance the metals (hydrogen is not considered a metal in this application): We have no metals in our equation, so move on to step 3 (the sodium is part of the catalyst so we don't consider it part of the balancing).
3.) Balance the nonmetals (not including oxygen). If you notice the left hand side of the equation has 3R groups and the right hand side only has one R-group. To fix this we can put a coefficient of 3 in front of 
On the left hand side of the equation we have 7 carbon atoms but on the right hand side we have 9 carbon atoms. This can be rectified by putting a coefficient of 3 in front of 
Now all the nonmetals (excluding oxygen) have been balanced and we can move on to step 4
4.) Balance oxygen. There are 9 oxygen atoms on both sides of the equation. Move on to step 5
5.) Balance Hydrogen. There are 17 hydrogens on both sides of the equation.
6.) Recount all atoms to make sure you have balanced correctly. 9 carbons on both sides, 3 R-groups on both sides, 9 oxygen on both sides, and 17 hydrogens on both sides.
If this problem had involved ionic species you would also want to make certain that the charges are balanced on both sides of the equation.
The charges on both sides add up to zero so your equation is balanced:
Example Question #431 : Ap Chemistry
Consider the following unbalanced reaction:
Once this equation has been balanced, what are the the respective stoichiometric coefficients (listed in the order in which the above compounds appear in the reaction)?
To balance chemical reactions, it's usually more effective to save the more common elements, such as oxygen, for last. For this reaction, let's go ahead and start by balancing the element 
Because there are 
Since we added a coefficient of 
Our final balanced equation looks like this.
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