Question

When 10 grams of methane is completely burnt in oxygen, the heat evolved is 560 KJ. What is the heat of combustion (in KJ/mol) of methane?
A. -1120
B. -968
C. -896
D. -560

Answer 1

Hint: Heat of combustion also known as calorific value is the amount of energy released when a compound under standard conditions undergoes complete combustion with oxygen. Calorific values are generally measured using a bomb calorimeter.

Complete step by step answer:
The chemical formula for methane is $C{H_4}$ and its molecular mass is calculated as the sum of Mass of the carbon atom and Mass of hydrogen atoms. The molar mass of carbon is 12g/mol and the mass of hydrogen atom is 1g. Therefore, the Molar mass of methane is:
$12 + 4 \times 1 = 16g/mol$
As we know, 10 gram of methane on combustion gives 560 KJ of heat. So 1 gram of methane on combustion gives = $\dfrac{{560}}{{10}}KJ$ of heat. Hence, 16 gram of methane on combustion give=$\dfrac{{560}}{{10}} \times 16 = 896KJ$
Thus the heat of combustion of methane is -896KJ/mol.

So, the correct answer is Option C.

Additional Knowledge:
1.The heat of combustion produced in the industrial process as waste is used for different processes such as:
2.To pre-heat the gas supplied for combustion and also used for heating the air for ventilation and other processes.
3.The heat received can be used for generating steam, hot water, and other products, this heat is normally sent out of the system using exhausts.

Note: The heat of combustion also known as heating value is determines in two ways:
1.Higher heating value(HCV): To calculate this heating value, we assume the water produced is in the liquid phase
2.Lower heating value (LCV): To calculate this heating value, we assume the water produced is in the vapor phase.