Question

In the combustion of $2.0gm$ of methane $25KCal$ heat is liberated, heat of combustion of methane would be.
A)$100Kcal$
B) $200Kcal$
C) $300Kcal$
D) $400Kcal$

Answer 1

We know that the heat of combustion of a substance, also referred to as the calorific value or the energy value, is often defined because the amount of warmth liberated while a given amount of the substance undergoes combustion.

Complete step by step answer:
The chemical reaction is,
$C{H_4} + 2C{O_2}\xrightarrow{{}}C{O_2} + 2{H_2}O$
We know that the molecular weight of methane is $16gm$.
The amount of heat liberated during the combustion of two gram of methane is $25Kcal$
We can calculate the heat of combustion of methane as follows.
The heat of combustion of methane $= \dfrac{{25 \times 16}}{2} = 200Kcal$

So, the correct answer is Option B.

Note:
Heat of combustion is usually categorized into the subsequent two types:
Higher calorific value also referred to as gross calorific value and better heating value.
Lower calorific value, also referred to as net calorific value and lower heating value.
Now we can see how to determine the upper and lower calorific value.

Determination of upper Calorific Value:
The higher calorific value of a substance is often determined by bringing back all the combustion products into the initial temperature. It’s important to notice that this also involves the condensation of any vapour that's produced during the combustion reaction. It also can be noted that these measurements are known to be performed under certain standard conditions during which the temperature of the reaction environment is kept at $25$ degrees Celsius.

Determination of Lower Calorific Value:
The lower calorific value of a substance, also mentioned because the net calorific value and therefore the lower heating value of the fuel, are often determined by subtracting the worth of the heat of transformation of vaporization of the water formed within the reaction from the worth of the gross calorific value. This type of expressing the warmth of combustion involves the idea that any water formed during the combustion reaction is within the sort of a vapour. Therefore, the energy that was expended during the reaction to convert the water into water vapor is taken into account during the calculation of this quantity.