When fuels are burnt, heat is produced. The amount of heat produced by different types of fuels on burning is expressed in terms of calorific value. Calorific value of a fuel may be defined as the amount of heat produced on complete burning of 1 gm of fuel. S.I. unit of calorific value of fuels is kilojoule per gram (KJ/g). For example, when one gram of wood is burnt completely it produces 17 kilojoules heat. Therefore, the calorific value of wood is 17 KJ/g. in similar manner, when 1 gm of kerosene oil is burnt completely it produces 48 kilojoules heat. So, the calorific value of kerosene oil is 48 KJ/g. the calorific value of different types of fuels is given in following table.
Table of calorific value of fuels
| Serial No. | Fuel | Calorific value |
| 1. | Hydrogen | 150 KJ/g |
| 2. | Methane | 55 KJ/g |
| 3. | LPG | 50 KJ/g |
| 4. | Kerosene oil | 48 KJ/g |
| 5. | Charcoal | 33 KJ/g |
| 6. | Wood | 17 KJ/g |
Significance of Calorific Value
It becomes clear from table given above that different fuels have different calorific values, i.e. different fuels produce different amounts of heat on burning. The calorific value of fuels helps us to decide that which fuel is good for us. This is done by comparing the calorific values of fuels with each other. Usually, a fuel having higher calorific value is considered to be a good fuel.
1) Case of Hydrogen Gas
Hydrogen gas has the highest calorific value of 150 KJ/g among all the fuels. So, hydrogen gas is considered to be an extremely good fuel. However, hydrogen gas is not used as a fuel in homes and industries. The main reasons for this are:
- Hydrogen gas is highly combustible and it burns with explosion when lighted.
- The storage and transportation of hydrogen gas from one place to another is very difficult.
- The cost of production of hydrogen gas is very high. So, it is an expensive fuel.
2) Case of Methane and Butane
Almost all the fuels consist of atoms of hydrogen and carbon. Since, the calorific value of fuels depends on the percentage of hydrogen present in them so the fuels which have higher percentage of hydrogen will have higher calorific value as compared to those fuels which have lower percentage of hydrogen. The percentage of hydrogen present in methane is 25% whereas the percentage of hydrogen present in butane is 17%. Due to this reason, methane has higher calorific value as compared to butane.
Test Your Understanding and Answer These Questions:
- What is calorific value?
- Give calorific value of different fuels?
- What is the significance of calorific value?
- Which fuel has higher calorific value out of methane and butane?