Does adding coefficients to a chemical equation disobey the law of definite proportions? explain your answer.

  No

Explanation:

- Law of definite proportions is a case from the Law of conservation of energy (matter) which states that "mass can neither be created nor destroyed, but changed from one form to another."

-  Adding coefficients to a chemical equation confirms that there is the same number of atoms on both sides of a reaction; therefore, matter has not been created or destroyed but reorganized to give new substrates.

Example :             2 Mg + O2 → 2 MgO              

In the balanced equation above, 2 moles of Mg reacts with 1 mole of O2 to produce 2 moles of MgO.

mass of 2 moles of Mg  = 24×2= 48 grams

mass of 1 mole of O2 = 16+16 = 32 grams

total mass of reactants = 48 + 32 = 80 grams

mass of 2 moles of MgO = (24+16) ×2 = 80 grams  

total mass of products = 80 grams

It is clear that the number of grams of matter before and after the reaction is the same and  equals to 80 grams, so obeys the law of definite proportions..