Question

The number of oxygen molecules used in the combustion of 1 molecule of ethanol is

• A. 1
• B. 2
• C. 3
• D. 4

Answer 1

The correct option is C

3

Explanation

• The reaction in which carbon compounds burns in oxygen to produce carbon dioxide $\left({\mathrm{CO}}_2\right)$, water $\left({\mathrm{H}}_2\mathrm{O}\right)$ along with the release of heat and light is known as combustion reaction. Since heat is released during the reaction thus, it is an exothermic reaction.
• When ethanol $\left({\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}\right)$ reacts with oxygen $\left({\mathrm{O}}_2\right)$, then the formation of carbon dioxide $\left({\mathrm{CO}}_2\right)$, and water $\left({\mathrm{H}}_2\mathrm{O}\right)$ takes place.
• The balanced chemical equation for the combustion reaction of ethanol is as follows:
• ${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}\left(\mathrm{l}\right)+3{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2{\mathrm{CO}}_2\left(\mathrm{g}\right)+3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)$

Thus, the above balanced equation defines that the combustion of 1 molecule of ethanol requires 3 molecules of oxygen.

Hence, the correct option is (C). The required oxygen molecules are equal to $3$.