Question

The incomplete combustion of gasoline produces \(\mathrm{CO}(\mathrm{g})\) as well as \(\mathrm{CO}_{2}(\mathrm{g}) .\) Write an equation for \((\mathrm{a})\) the complete combustion of the gasoline component octane, \(\mathrm{C}_{8} \mathrm{H}_{18}(\mathrm{l}),\) and \((\mathrm{b})\) incomplete combustion of octane with \(25 \%\) of the carbon appearing as \(\mathrm{CO}(\mathrm{g})\)

Short answer

The reaction equations for the complete and incomplete combustion of octane are:Complete combustion: \(C_8H_{18}(l) + 12.5O_2(g) \rightarrow 8CO_{2}(g) + 9H_{2}O(l)\)Incomplete combustion (25% CO): \(C_8H_{18}(l) + 9.5O_2(g) \rightarrow 6CO_{2}(g) + 2CO(g) + 9H_{2}O(l)\)

Step-by-step solution

Complete Combustion of Octane

Complete combustion of a hydrocarbon involves reaction with oxygen to produce only carbon dioxide (CO2) and water (H2O). So, this combustion can be represented as: \(C_8H_{18}(l) + 12.5O_2(g) \rightarrow 8CO_{2}(g) + 9H_{2}O(l)\)In this reaction, octane (C8H18) is combusted completely, resulting in 8 molecules of CO2 and 9 molecules of H2O.

Determine Carbon in CO for Incomplete Combustion

For incomplete combustion, where 25% of carbon is converted into CO, first calculate how many carbon atoms will be appearing as CO: 25% of 8 Carbon atoms in Octane = 0.25 * 8 = 2 Hence, 2 out of 8 carbon atoms will appear as CO.

Incomplete Combustion of Octane

Now that we know 2 carbon atoms end up as CO, the rest 6 Carbon atoms will go to CO2. So, for incomplete combustion, the reaction would look like this:\(C_8H_{18}(l) + 9.5O_2(g) \rightarrow 6CO_{2}(g) + 2CO(g) + 9H_{2}O(l)\)Here, the octane (C8H18) is not combusted completely, leading to production of 2 molecules of CO, 9 molecules of H2O and 6 molecules of CO2.

Key concepts

Incomplete Combustion

When hydrocarbons such as octane do not burn fully, the process is called incomplete combustion. This occurs when there isn't enough oxygen to allow the fuel (in this case, octane) to react fully to form carbon dioxide and water.
During incomplete combustion, some of the carbon atoms in the fuel react with oxygen to form carbon monoxide (\(\text{CO}\)). Carbon monoxide is a dangerous gas because it can bind to hemoglobin in blood more effectively than oxygen, minimizing the amount of oxygen carried in the bloodstream. In our given scenario, 25% of the carbon atoms in octane are converted to CO, while the rest are transformed into carbon dioxide (\(\text{CO}_2\)).
The chemical equation for the incomplete combustion of octane can be represented as follows:- Octane (\(\text{C}_8\text{H}_{18}\)) reacts with 9.5 molecules of oxygen (\(\text{O}_2\))- Yields 6 molecules of carbon dioxide (\(\text{CO}_2\))- Produces 2 molecules of carbon monoxide (\(\text{CO}\))- And 9 molecules of water (\(\text{H}_2\text{O}\))
In summary, this process results in both carbon dioxide and carbon monoxide. It highlights the inefficiency of incomplete combustion in terms of energy release and potential health hazards.

Complete Combustion

Complete combustion occurs when a hydrocarbon, like octane, burns in the presence of excess oxygen. In this reaction, all carbon atoms in the fuel are converted into carbon dioxide (\(\text{CO}_2\)), and hydrogen atoms turn into water (\(\text{H}_2\text{O}\)). This process is more efficient than incomplete combustion, producing more energy.
The complete combustion of octane can be described by the chemical equation:- Octane (\(\text{C}_8\text{H}_{18}\)) reacts with 12.5 molecules of oxygen (\(\text{O}_2\))- Results in 8 molecules of carbon dioxide (\(\text{CO}_2\))- And forms 9 molecules of water (\(\text{H}_2\text{O}\))
This reaction is crucial in engines since it maximizes energy production. In an ideal scenario, engines achieve complete combustion, which not only boosts efficiency but also minimizes harmful emissions such as carbon monoxide.

Octane Combustion

Octane, \(\text{C}_8\text{H}_{18}\), is a primary component of gasoline. Its combustion is important for understanding how fuel energy is harnessed in car engines. Whether complete or incomplete, octane combustion is a fundamental process in energy production.

• Complete Combustion: Maximizes energy and forms only carbon dioxide and water.
• Incomplete Combustion: Produces carbon monoxide along with carbon dioxide, reducing efficiency and creating harmful by-products.

In practical use, ensuring sufficient oxygen supply to achieve complete combustion is key for optimal performance and reduced emissions. However, factors like air-fuel ratio, engine design, and operational conditions can result in incomplete burning, leading to pollutants like carbon monoxide.
Understanding these processes is crucial for improving automotive technologies and fuel efficiencies, thus lowering environmental pollution and enhancing energy savings.