Question

Which of the following reactions is not correct according to the law of conservation of mass.
(i) 2Mg(s) + O2(g) → 2MgO(s)
(ii) C3H8(g) + O2(g) → CO2(g) + H2O(g)
(iii) P4(s) + 5O2(g) → P4O10(s)
(iv) CH4(g) + 2O2(g) → CO2(g) + 2H2O (g)

Answer 1

(ii)C3H8(g) + O2(g) ⇒ CO2(g) +H2O(g)  -   is the answer.

Answer 2

Answer : The incorrect option is, (ii) $C_3H_8(g)+O_2(g)\rightarrow CO_2(g)+H_2O(g)$

Explanation :

According to the law of conservation of mass, the total mass of reactant must be equal to the total mass of product. The mass remains conserved.

That means, Mass of reactant = Mass of product

Or we can say that, the balanced chemical equation or reaction always follow the law of conservation of mass not unbalanced reaction.

(i) $2Mg(s)+O_2(g)\rightarrow 2MgO(s)$

This reaction is a balanced reaction. So, this reaction follow the law of conservation of mass.

(ii) $C_3H_8(g)+O_2(g)\rightarrow CO_2(g)+H_2O(g)$

This reaction is an unbalanced reaction. So, this reaction does not follow the law of conservation of mass.

(iii) $P_4(s)+5O_2(g)\rightarrow P_4O_{10}(s)$

This reaction is a balanced reaction. So, this reaction follow the law of conservation of mass.

(iv) $CH_4(g)+2O_2(g)\rightarrow CO_2(g)+2H_2O(g)$

This reaction is a balanced reaction. So, this reaction follow the law of conservation of mass.

Hence, (ii) $C_3H_8(g)+O_2(g)\rightarrow CO_2(g)+H_2O(g)$ this reaction does not follow the law of conservation of mass.