Question

How does the law of conservation of mass apply to this reaction: C2H4 + O2 → H2O + CO2?

Answer 1

The correct answer is D. The law of conservation of mass states that in a system matter can neither be created or destroyed, hence atoms of each element on reactant side should equal atoms of each element on product side. In the unbalanced equation:

$C_2H_4 + O_2 ==> H_2O + CO_2$, the are 2 carbon atoms on reactant side as opposed to 1 carbon atom on product side,  there are 4 hydrogen atoms on reactant side as opposed to 2 hydrogen atoms on product side, and there are 2 oxygen atoms on reactant side as opposed to 3 atoms of oxygen on product side. To balance the equation we add a coefficient of 3 on O_2 and on the product side we put a coefficient of 2 on both water $H_2O$ and carbon dioxide $CO_2$.

$C_2H_4 + 3O_2 ==> 2H_2O + 2CO_2$.

Answer 2

The answer is a

the equation needs to be balanced. There are fewer oxygen atoms in the equation than hydrogen or a carbon