Question

The main combustible component in most common fuels (solid, liquid and gas) is

• A. Oxygen
• B. Nitrogen
• C. Argon
• D. Carbon and Hydrogen

Hint:

The ratio of hydrogen to carbon in a fuel determines its calorific value and carbon footprint, with hydrogen-rich fuels releasing more energy per unit mass and producing less \( \text{CO}_2 \).

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks for the primary element(s) that undergo combustion reactions to release thermal energy in typical fuels.

Step 2: Key Formula or Approach:
Combustion is a rapid exothermic oxidation chemical reaction.
The fundamental combustion chemical equations for fuel components are:
\[ \text{C} + \text{O}_2 \rightarrow \text{CO}_2 \quad (\Delta H^\circ = -393.5\text{ kJ/mol}) \]
\[ 2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O} \quad (\Delta H^\circ = -241.8\text{ kJ/mol per mole of gas}) \]

Step 3: Detailed Explanation:

• Hydrocarbon Nature of Fuels: Most natural and synthetic fuels (such as coal, coke, petroleum, natural gas, gasoline, and diesel) are composed primarily of hydrocarbons or elemental carbon.
The oxidation of carbon and hydrogen atoms present in these fuels releases large amounts of energy due to the formation of highly stable chemical bonds in carbon dioxide (\( \text{CO}_2 \)) and water vapor (\( \text{H}_2\text{O} \)).

• Role of Other Elements:
-

Oxygen (Option A) is the oxidant required to support combustion, but it is not the combustible fuel component itself.
-

Nitrogen (Option B) and

Argon (Option C) are chemically inert in typical combustion processes. They do not combust and instead act as thermal diluents in combustion air, carrying away some sensible heat.


Step 4: Final Answer:
Thus, the main combustible components in common fuels are carbon and hydrogen, matching Option (D).