I think you are asking about balancing the chemical equation. The equation you have given is written below:
H2SO4 + Ba --> BaSO4 + H2
This reaction is already fully balanced. We can tell this by the number of each different type of atom on each side of the equation. There are two hydrogens on either side, one barium, one sulfur, and four oxygens on either side. This means that the equation is balanced as is. So you only need one mole of each reactant to fully react with each other.