Question

What is the coefficient of oxygen if the equation for the reaction is balanced with whole-number coefficients?
$\ldots \ldots {{C}_{2}}{{H}_{2}}\left( g \right)+\ldots \ldots \ldots {{O}_{2}}\left( g \right)\to ~\ldots ..C{{O}_{2}}\left( g \right)\text{ }+\text{ }\ldots ..{{H}_{2}}O\left( l \right)$

A. 1
B. 2
C. 3
D. 4
E. 5

Answer 1

Hint We have to go for trial and error method means we have to put the values which are given in the options one by one and check that the number of atoms is balanced in the given chemical reaction or not on both sides.

Complete step by step answer:
 - In the question it is given a chemical reaction without coefficients. We have to balance the chemical reaction using the coefficients given in the options.
- First we have to take the unbalanced reaction given in the question and it is as follows.
\[{{C}_{2}}{{H}_{2}}\left( g \right)+{{O}_{2}}\left( g \right)\to ~C{{O}_{2}}\left( g \right)\text{ }+\text{ }{{H}_{2}}O\left( l \right)\]
- First we have to balance the carbon atoms on both of the given chemical reactions.
\[{{C}_{2}}{{H}_{2}}\left( g \right)+{{O}_{2}}\left( g \right)\to ~2C{{O}_{2}}\left( g \right)\text{ }+\text{ }{{H}_{2}}O\left( l \right)\]
- In the second step we have to balance the hydrogen atoms.
\[{{C}_{2}}{{H}_{2}}\left( g \right)+{{O}_{2}}\left( g \right)\to ~2C{{O}_{2}}\left( g \right)\text{ }+\text{ 2}{{H}_{2}}O\left( l \right)\]
- Now in the last step we have to balance the oxygen atoms.
\[{{C}_{2}}{{H}_{2}}\left( g \right)+3{{O}_{2}}\left( g \right)\to ~2C{{O}_{2}}\left( g \right)\text{ }+\text{ 2}{{H}_{2}}O\left( l \right)\]
- Now the total chemical reaction is balanced, one mole of acetylene reacts with 3 moles of oxygen and forms 2 moles of carbon dioxide and 2 moles of water as the products.
- Therefore the coefficient of oxygen in the balanced chemical reaction is 3.

- So, the correct option is C.

Note: Balanced chemical reaction means the number of atoms of the same element on the reactant side should be equal to the number atoms of the same element on the product side. Then only it is called a balanced chemical reaction or equation.