13.20 Hexane (C6 H14) burns with air to give products with...

13.20 Hexane $\left(\mathrm{C}_{6} \mathrm{H}_{14}\right)$ burns with air to give products with the dry molar analysis of $\mathrm{CO}_{2}, 11.5 \% ; \mathrm{CO}, 2.4 \% ; \mathrm{O}_{2}, 2.0 \% ; \mathrm{H}_{2}$, $1.6 \% ; \mathrm{N}_{2}, 82.5 \% .$ Determine the air-fuel ratio on a molar basis.

Key Concepts

Composition of Air in Combustion Processes

Air is not a pure substance but a mixture of gases, primarily oxygen and nitrogen. In combustion processes, the composition of air—commonly taken as roughly 21% oxygen and 79% nitrogen by volume—must be considered to accurately calculate the amount of oxygen available for the reaction. This composition significantly influences the stoichiometry and overall efficiency of the combustion process.

Molar Analysis of Reaction Products

Molar analysis involves quantifying the mole fractions or percentages of the various gases present in the combustion products. This approach provides insight into the reaction's efficiency and the completeness of the combustion process, helping to identify any deviations from the ideal, stoichiometric combustion scenario.

Combustion Reaction Stoichiometry

This concept involves writing and balancing the chemical equation for the combustion of a fuel with an oxidizer. It requires accounting for every atom in the molecules involved so that the number of atoms of each element is conserved, ensuring the reaction is balanced on both sides. Stoichiometry lays the groundwork for relating the amounts of reactants to the amounts of products formed during combustion.

Air-Fuel Ratio

The air-fuel ratio is a measure of the amount of air that is mixed with a given amount of fuel to achieve a complete combustion. It is typically expressed on a molar or mass basis and is crucial for optimizing combustion efficiency and minimizing pollutants. This ratio determines whether the combustion is stoichiometric, fuel-rich, or air-rich.

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