According to the law of conservation of mass, mass can neither be created nor be destroyed. Thus the mass of products has to be equal to the mass of reactants. The number of atoms of each element has to be same on reactant and product side. Thus chemical equations are balanced.
Combustion is a chemical reaction in which hydrocarbons are burnt in the presence of oxygen to give carbon dioxide and water.
The balanced reaction for combustion of butanoic acid is:
You can look at the number of valence electrons and look at the size of the molecule itself to determine which element in this certain group is shown on the model.
