What is the balanced chemical equation for the reaction of acetic acid with limestone CaCO3?
That's a good question. I have to admit most of the time I balance equations by intuition rather than any systematic method, however I think of a few rules to follow when balancing these equations.
Balancing chemical equations all comes down to one principle, conservation of atoms. The same number and types of atoms that you put in must still be there after the reaction occurs (since a chemical reaction can't change one element to another). Let's take a somewhat simple example, the combustion of sucrose (a sugar):
Here A,B,C,and D are the number of moles reacted/produced of sucrose, oxygen, carbon dioxide, and water respectively. One way to make this balancing simple is to look for molecules with unique atoms on either side of the equation. For example both molecules on the reactant side, sucrose and oxygen, contain oxygen. However, only sucrose has carbon and hydrogen. You'll also notice that on the product side both carbon dioxide have oxygen, however only carbon dioxide and water is the only one on this side that has hydrogen. So what does that tell us?
First the only reactant with carbon is sucrose and the only product with carbon is carbon dioxide this means that all the carbon
from the reacted sucrose goes into the CO2. That means for every sucrose reacted 12 CO2's are made (since sucrose has 12 carbons). This also means that the reaction coefficients A and C have the following relation:
This means we can now write the reaction like this:
In addition sucrose is the only reactant with hydrogen, therefore by the same reasoning for every sucrose molecule 22/2=11 water molecules are made. This results in the following relation for reaction coefficients A and D:
We can now write the reaction like this:
So now we only need to find out how much molecular oxygen we need for every sucrose molecule. We know that for every sucrose molecule we have enough carbon and hydrogen for 12 carbon dioxide molecules and 11 water molecules, however does the sucrose molecule have enough oxygen for these carbon dioxide and water molecules? A sucrose molecule has 11 oxygen atoms, while 12 carbon dioxide molecules has 24 oxygen atoms and 11 water molecules has 11 oxygen atoms. By this count we are 24 oxygen atoms short (24+11-11=24), therefore we need 12 O2 molecules to make up this difference (12*2=24). Therefore we need 12 oxygen molecules for every sucrose molecule, this means we can write the following relation between reaction coefficients A and B: