Ncert Exercises & Solutions

Identify the reaction that does not obey the law of conservation of mass from the provided options:

1. $2 Mg (s) + O_{2} (g) \to 2 MgO (s)$

2. $C_{3} H_{8} (g) + O_{2} (g) \to {CO}_{2} (g) + H_{2} O (g)$

3. $P_{4} (s) + 5 O_{2} (g) \to P_{4} O_{10} (s)$

4. ${CH}_{4} (g) + 2 O_{2} (g) \to {CO}_{2} (g) + 2 H_{2} O (g)$

Hint: Law of conservation of mass

In this equation,

\underset{44}{C_{3} H_{8} (g)}

g + \underset{32}{O_{2} (g)}

g \to \underset{44}{{CO}_{2} (g)}

g + \underset{18}{H_{2} O (g)}

g

i.e., mass of reactants

\neq

mass of products.

Hence, law of conservation of mass is not followed.