How can I tell if a chemical reaction is balanced or not balanced?
If the equation has the same number of each type of atom on both sides of the arrow, it is balanced. If the number of atoms on each side of the arrow is not the same, the equation is not balanced. For example, in the equation H2 + O2 -->H2O, there are two hydrogen atoms and two oxygen atoms on the left, and two hydrogen atoms and one oxygen atom on the right. Therefore, the equation is not balanced. However, in the equation 2H2 + O2 -->2H2O, there are four hydrogen atoms and two oxygen atoms on the left and four hydrogen atoms and two oxygen atoms on the right, so the equation is balanced.
A chemical reaction is always balanced, because chemical reactions follow the laws of conservation of mass and conservation of matter. A chemical equation for the reaction is balanced if and only if the same total numbers of each kind of atomic symbol appear on both the left and right sides of the equation.