Question

How does the law of conservation of mass apply to this reaction: C2H4+O2-->2H2O+2CO2?

Answer 1

Add a coefficient of 3 in front of the 02 to balance the 6 O atoms in the products

Answer 2

Answer: Option (b) is the correct answer.

Explanation:

According to the law of conservation of mass, mass of reactants will be equal to the mass of products in a chemical reaction.

For example, $C_{2}H_{4} + O_{2} \rightarrow 2H_{2}O + 2CO_{2}$

Here, mass of the reactants is (28.05 + 16) g/mol = 44.05 g/mol

Mass of the products is $(2 \times 18 + 2 \times 44)$ g/mol = 36 + 88 = 124 g/mol

Therefore, mass of reactants is not equal to the mass of products. Since, there are equal number of hydrogen and carbon atoms on both the sides and only the oxygen atoms needs to be balanced.

Thus, we can conclude that for the given equation only the oxygen needs to be balanced. There are equal numbers of hydrogen and carbon.