HOw does the law of conservation of mass apply to this reaction C2H4 + 3O2 2H2O + 2CO2

The law of conservation of mass is applied to determine whether a reaction is balanced or not. In the case where the reaction is not, it must be balanced.

Explanation:

You have the reaction:

C₂H₄ + 3 O₂ ⇒ 2 H₂O + 2 CO₂

The law of conservation of matter states that since no atom can be created or destroyed in a chemical reaction, so the number of atoms that are present in the reagents has to be equal to the number of atoms present in the products.

Then, you must balance the chemical equation. For that, you must first look at the subscripts next to each atom to find the number of atoms in the equation. If the same atom appears in more than one molecule, you must add its amounts

Left side: 2 carbon, 4 hydrogen and 2 oxygen.

Right side: 1 carbon, 2 hydrogen and 3 oxygen.

The coefficients of each molecule below indicate the amount of each molecule for the reaction. This coefficient can be modified to balance the equation, just as you should never alter the subscripts.

By multiplying the coefficient mentioned by the subscript, you get the amount of each element present in the reaction. So, in this case you can see that in the reaction there is:

Left side: 1*2=2 carbon, 1*4=4 hydrogen and 3*2=6 oxygen.

Right side: 2*1=2 carbon, 2*2=4 hydrogen and 2*1+2*2=6 oxygen.

You have the same amount of elements on each side of the reaction. This means that the equation is balanced.

In summary, the law of conservation of mass is applied to determine whether a reaction is balanced or not. In the case where the reaction is not, it must be balanced.

There are fewer oxygen atoms in the equation than hydrogen or carbon. Only the oxygen needs to be balanced. There are equal numbers of hydrogen and carbon.