Question

(b) What is enthalpy of combustion? Explain its use.

Answer 1

There are several chemical reactions which we can observe in surrounding such as combustion, corrosion, precipitation etc. Let’s discuss about combustion reaction. It is an example of an oxidation reaction in which chemical substances react with oxygen to oxidise them and form oxidised products. For example combustion of methane results the formation of carbon dioxide gas and water vapour. 

Usually combustion of all hydrocarbons finally forms carbon dioxide gas and water vapour. The incomplete combustion occurs in the limited supply of oxygen. It forms hazardous products like carbon monoxide gas and water vapour. Combustion is an exothermic reaction which releases a large amount of energy. This energy change is called as the enthalpy of combustion. The combustible substances like wood and other many common items are organic because they are composed of C, H and O. An essential condition for combustion reaction is the presence of oxygen gas. You can observe the combustion process in candle, in which flame can only burn in the presence of oxygen. 

Another example of this process is combustion of methane which also forms CO2, and H2O with large amount of energy. 

CH4CH4 + O2O2 →→ CO2CO2 + H2OH2O + heat


The combustion of metals changes them to metallic oxides such as burning of magnesium form magnesium oxide with heat.

2Mg + O2O2 →→ 2MgO