Question

In the combustion of $4g$of $C{H_4}$, $2.5kcal.$of heat is liberated. The heat of combustion of$C{H_4}$is: $$
(a) 20 Kcal
(b) 10 Kcal
(c) 2.5 Kcal
(d) 5 Kcal

Answer 1

Hint: Combustion of substance is also known as reaction of substance with oxygen by heating. On combustion, substance undergoes oxidation.

Complete step by step answer:
Methane is a chemical compound with formula $C{H_4}$. It is the simplest alkane and it is a main constituent of natural gas. Methane is a tetrahedral molecule with four equivalent $C - H$ bonds i.e.

At room temperature and pressure methane, is a colourless, odourless and flammable gas. Methane is used as fuel in many industries and is used in generating thermal electricity. Methane is also used as rocket fuel. Natural gas, which is mostly composed of methane is used to produce hydrogen gas on industrial scale by treating it with water i.e.
$C{H_4} + {H_2}O \to CO + 3{H_2}$
Combustion of methane means that methane is heated in the presence of oxygen. The reaction produces carbon dioxide and water as the product. I.e.
$C{H_4} + {O_2} \to C{O_2} + {H_2}O$
The process of combustion releases energy. Since the energy is released in chemical reactions, thus it is an exothermic reaction.
Now according to the question, combustion of \[4g{\text{ }} of {\text{ }}C{H_4}\]\[\] produces \[2.5kcal\] of heat. The molecular of $C{H_4}$. Thus molecular mass of $C{H_4}$ will be ix atomic mass of carbon $ + 4x$ atomic mass of hydrogen atom we know that atomic mass of carbon and hydrogen is $12g\;{\text{and 1g}} {\text{.}}$ so, the nuclear mass of $C{H_4}$ will become $ = 16g$
Combustion of \[4g{\text{ }}of\;C{H_4}\] produce heat = \[2.5kcal.\]
Then combustion of \[16g\] of \[C{H_4}\] produces heat.
Combustion of 1 mole of \[C{H_4}\] produces heat. \[ = \dfrac{{2.5kcal}}{{4g}} \times 16g\]
\[ = 10kcal.\]
Hence heat of combustion of \[C{H_4}\]is \[10.kcal\]

So, the correct answer is Option B .

Note:
In this question, we have used the concept of molecular mass. Molecular mass is defined as the average relative mass of its molecular as compared with an atom of \[carbon - 12\] isotope. We have measured molecular mass in grams, which is known as green molecule mass.