Adding coefficients to a chemical equation does not disobey the law of definite proportions. In fact, it's a necessary part of balancing chemical equations, which is essential for upholding the law of definite proportions.

Here's why:

* The Law of Definite Proportions: This law states that a chemical compound always contains the same elements in the same proportions by mass, regardless of its source. For example, water (H₂O) will always have two hydrogen atoms for every one oxygen atom.

* Balancing Chemical Equations: Coefficients are numbers placed in front of chemical formulas in an equation to ensure that the number of atoms of each element on the reactant side (left) is equal to the number of atoms of that element on the product side (right). This ensures that the total mass of the reactants equals the total mass of the products, following the law of conservation of mass.

Example:

Let's look at the combustion of methane:

Unbalanced Equation: CH₄ + O₂ → CO₂ + H₂O

This equation is unbalanced because:

* There is 1 carbon atom on the reactant side but 1 on the product side.

* There are 4 hydrogen atoms on the reactant side but 2 on the product side.

* There are 2 oxygen atoms on the reactant side but 3 on the product side.

Balanced Equation: CH₄ + 2O₂ → CO₂ + 2H₂O

By adding coefficients, we balance the equation:

* There is 1 carbon atom on each side.

* There are 4 hydrogen atoms on each side.

* There are 4 oxygen atoms on each side.

Conclusion: Adding coefficients in a chemical equation is essential for balancing the equation, which in turn ensures that the chemical reaction adheres to the law of definite proportions. The coefficients represent the number of moles of each reactant and product involved in the reaction, ensuring that the mass of the reactants and products remains consistent.