Question

When the equation $\mathrm{\_}{C}_3{H}_8+\mathrm{\_}{O}_2\to \mathrm{\_}C{O}_2+\mathrm{\_}{H}_{2}O$ is balanced using the lowest whole number coefficients, the coefficient before $O_2$ will be:
A. 1
B. 2.5
C. 5
D. 10
E. 13

Answer 1

Hint: Chemical reaction which is represented in the form of symbols (substances) is known as a chemical equation. A chemical reaction or equation consists of reactants, products, and an arrow showing the direction of the reaction and the product. A chemical reaction that contains the same number of atoms of all the molecules on both sides is known as a balanced chemical equation. Balancing of a chemical equation is governed by the law of conservation of mass. According to the law of conservation of mass, mass can neither be created nor destroyed in a chemical reaction due to this the total mass of the element present on the reactant should be equal to the total mass of the element present on the product side. If a chemical reaction does not follow the law of conservation of mass then the chemical reaction is said to be an unbalanced chemical equation.

Complete step by step answer:
Let us balance the given chemical equation:
$\mathrm{\_}{C}_3{H}_8+\mathrm{\_}{O}_2\to \mathrm{\_}C{O}_2+\mathrm{\_}{H}_{2}O$
The balanced chemical equation will be
$C_3{H}_8+5O_2\to 3C{O}_2+4H_{2}O$

Element	Number of atoms on the reactant side	Number of atoms on the product side
Carbon (C)	3	3
Oxygen (O)	10	10
Hydrogen (H)	8	8

So we can see that all the number of atoms in the reactant and on the product side are equal due to which the total mass on the reactant side will be equal to the product side and hence it obeys the law of conservation of mass. Therefore, the given chemical reaction is balanced. Except 5 if we use other numbers which are given in the options the given chemical equation cannot be balanced.
Therefore, the co-efficient before $O_2$ will be 5.

So, the correct answer is Option C .

Note: The stoichiometric coefficient shows the total number of molecules of a chemical species that participate in the chemical reaction. The stoichiometric coefficient provides a ratio between the reacting species and the products formed in the chemical reaction.