Question

The complete combustion of $1$ mole of pentene, ${{\text{C}}_{\text{5}}}{{\text{H}}_{{\text{12}}}}$, will require how many moles of oxygen, ${{\text{O}}_{\text{2}}}$ ?

Answer 1

To answer this question we should know what combustion reactions are and what are the products of combustion reactions. Combustion reactions are defined as the reaction in which the chemical substance reacts with oxygen and forms carbon dioxide and water and releases the energy. We will count the total number of oxygen atoms present in both products to determine the moles of oxygen.

Complete step-by-step answer: The reaction in which a chemical substance or hydrocarbons react with oxygen and produce carbon dioxide and water and release the energy in form of light and heat is known as combustion reaction.
A general combustion reaction is represented as follows:
${{\text{C}}_{\text{n}}}{{\text{H}}_{{\text{2n}}}}\,{\text{ + }}\,\,{{\text{O}}_{\text{2}}}\,\mathop \to \limits^\Delta \,{\text{nC}}{{\text{O}}_{\text{2}}}\,{\text{ + }}\,{\text{n}}{{\text{H}}_{\text{2}}}{\text{O}}$
Where,${{\text{C}}_{\text{n}}}{{\text{H}}_{{\text{2n}}}}$is a hydrocarbon. Where n is the number of carbons atoms.The combustion reaction of hydrocarbons gives carbon dioxide and water. The number of carbon atoms in carbon dioxide depends upon the number of carbon atoms present in hydrocarbons and number of hydrogen atoms in water depend upon the number of hydrogen atoms present in hydrocarbons.The equation for the combustion of pentene is represented as follows:
${{\text{C}}_5}{{\text{H}}_{12}}\,{\text{ + }}\,\,{\text{n}}{{\text{O}}_{\text{2}}}\,\mathop \to \limits^\Delta \,5\,{\text{C}}{{\text{O}}_2}\, + \,6\,{{\text{H}}_{\text{2}}}{\text{O}}$
We have five mole of carbon atoms in pentane, so five moles of carbon dioxide will produce and we have twelve moles of hydrogen atoms in pentane, so twelve moles of water will produce.
Now, the total moles of oxygen atoms in products, carbon dioxide and water is sixteen (ten moles oxygen in carbon dioxide and six moles oxygen in water).
So, we require sixteen moles of oxygen atoms to prepare the five mole of carbon dioxide and six moles of water.Now, the oxygen is diatomic means one mole oxygen will give two moles of oxygen atoms and we require sixteen moles of oxygen atoms, so we will take eight moles of oxygen.
So, the combustion of one mole of pentene is shown as follows:
${{\text{C}}_5}{{\text{H}}_{12}}\,{\text{ + }}\,\,8{{\text{O}}_{\text{2}}}\,\mathop \to \limits^\Delta \,5\,{\text{C}}{{\text{O}}_2}\, + \,6\,{{\text{H}}_{\text{2}}}{\text{O}}$

Therefore, $8$ moles of oxygen, ${{\text{O}}_{\text{2}}}$ is required for the complete combustion of pentene.

Note: The general formula for hydrocarbon is${{\text{C}}_{\text{n}}}{{\text{H}}_{{\text{2n}}}}$. The burning of wood or coal in winter at home is an example of combustion reactions. Production of energy in thermal power plants and the burning of petrol and diesel in cars are also the example of combustion reactions. Combustion reactions require high temperatures. The combustion reaction produces released energy, so these are exothermic reactions. Products of combustion reactions are gases. The number of carbon atoms represents the mole of products produced by one mole of hydrocarbon.