Question

Write a balanced chemical equation for the complete combustion of each of the following compounds: a. hexane b. cyclopentane, ${\mathrm{C}}_5{\mathrm{H}}_{10}$ c. 2 -methylbutane

Short answer

2C_6 H_{14} + 19O_2 \rightarrow 12CO_2 + 14H_2O; 2C_5 H_{10} + 15O_2 \rightarrow 10CO_2 + 10H_2O; C_5 H_{12} + 8O_2 \rightarrow 5CO_2 + 6H_2O.

Step-by-step solution

Identify the General Combustion Reaction

The general formula for the complete combustion of a hydrocarbon is: $$\text{Hydrocarbon}+\text{Oxygen}\to \text{Carbon Dioxide}+\text{Water}$$

Write the Formula for Hexane

Hexane is a hydrocarbon with the chemical formula ${\text{C}}_6{\text{H}}_{14}$. For complete combustion, the reaction is: $${\text{C}}_6{\text{H}}_{14}+{\text{O}}_2\to {\text{CO}}_2+{\text{H}}_2\text{O}$$

Balance the Hexane Combustion Equation

Balance the atoms in the equation: $${\text{C}}_6{\text{H}}_{14}+9.5{\text{O}}_2\to 6{\text{CO}}_2+7{\text{H}}_2\text{O}$$Since fractional coefficients are not preferred, multiply the entire equation by 2:$$2{\text{C}}_6{\text{H}}_{14}+19{\text{O}}_2\to 12{\text{CO}}_2+14{\text{H}}_2\text{O}$$

Write the Formula for Cyclopentane

Cyclopentane has the chemical formula ${\text{C}}_5{\text{H}}_{10}$. The reaction for its complete combustion is: $${\text{C}}_5{\text{H}}_{10}+{\text{O}}_2\to {\text{CO}}_2+{\text{H}}_2\text{O}$$

Balance the Cyclopentane Combustion Equation

Balance the atoms in the equation: $${\text{C}}_5{\text{H}}_{10}+7.5{\text{O}}_2\to 5{\text{CO}}_2+5{\text{H}}_2\text{O}$$Multiplying the entire equation by 2, we get:$$2{\text{C}}_5{\text{H}}_{10}+15{\text{O}}_2\to 10{\text{CO}}_2+10{\text{H}}_2\text{O}$$

Write the Formula for 2-Methylbutane

2-Methylbutane has the chemical formula ${\text{C}}_5{\text{H}}_{12}$. The reaction for its complete combustion is: $${\text{C}}_5{\text{H}}_{12}+{\text{O}}_2\to {\text{CO}}_2+{\text{H}}_2\text{O}$$

Balance the 2-Methylbutane Combustion Equation

Balance the atoms in the equation: $${\text{C}}_5{\text{H}}_{12}+8{\text{O}}_2\to 5{\text{CO}}_2+6{\text{H}}_2\text{O}$$

Key concepts

Balancing Chemical Equations

To understand combustion reactions, it is crucial to balance chemical equations. This ensures that the same number of each type of atom is present on both sides of the equation.
Balancing chemical equations involves:

• Identifying the reactants and products
• Writing their formulas correctly
• Using coefficients in front of formulas to ensure equal numbers of atoms

For example, during combustion, hydrocarbons react with oxygen to produce carbon dioxide and water. As seen in the combustion of hexane:
$${\text{C}}_6{\text{H}}_{14}+9.5{\text{O}}_2\to 6{\text{CO}}_2+7{\text{H}}_2\text{O}$$
It is common to multiply the equation by 2 to get whole numbers: $$2{\text{C}}_6{\text{H}}_{14}+19{\text{O}}_2\to 12{\text{CO}}_2+14{\text{H}}_2\text{O}$$
Practice more to master balancing equations!

Hydrocarbons

Hydrocarbons are organic compounds made up entirely of hydrogen and carbon atoms. They are classified based on the types of bonds between carbon atoms.
Examples include:

• Alkanes (single bonds): methane, hexane
• Cycloalkanes (ring structures): cyclopentane
• Branched alkanes: 2-methylbutane

Each type of hydrocarbon has a different structure, affecting its properties and reactions. For example:
$${\text{C}}_6{\text{H}}_{14}\to \text{Hexane}$$
$${\text{C}}_5{\text{H}}_{10}\to \text{Cyclopentane}$$
$${\text{C}}_5{\text{H}}_{12}\to \text{2-Methylbutane}$$
Understanding their formulae is vital for predicting and balancing their combustion reactions.

Complete Combustion

Complete combustion involves burning a hydrocarbon in excess oxygen, resulting in carbon dioxide and water. This process releases energy and is a fundamental reaction in organic chemistry.
The general equation for complete combustion is: $$\text{Hydrocarbon}+\text{Oxygen}\to \text{Carbon Dioxide}+\text{Water}$$ For instance, in hexane: $${\text{C}}_6{\text{H}}_{14}+19{\text{O}}_2\to 12{\text{CO}}_2+14{\text{H}}_2\text{O}$$
Complete combustion is efficient because it fully converts fuel into end products, producing more energy compared to incomplete combustion which forms soot and carbon monoxide.

Hexane Combustion

Hexane (\text{C}_6 \text{H}_{14}) is an alkane containing six carbon atoms. In a complete combustion reaction:

• Reactants: Hexane and oxygen
• Products: Carbon dioxide and water

The balanced equation is: $$2{\text{C}}_6{\text{H}}_{14}+19{\text{O}}_2\to 12{\text{CO}}_2+14{\text{H}}_2\text{O}$$
Start by balancing carbons, then hydrogens, and finally oxygens. Remember that the number of atoms on each side of the equation must match.
In real-life applications, hexane combustion is utilized in industries for energy production.

Cyclopentane Combustion

Cyclopentane (\text{C}_5 \text{H}_{10}) is a cyclic alkane with a five-carbon ring. During its complete combustion:

• Reactants: Cyclopentane and oxygen
• Products: Carbon dioxide and water

The balanced equation is: $$2{\text{C}}_5{\text{H}}_{10}+15{\text{O}}_2\to 10{\text{CO}}_2+10{\text{H}}_2\text{O}$$
This involves balancing the number of carbon, hydrogen, and oxygen atoms to ensure the equation is correct.
Cyclopentane is often used as a solvent and in the production of resins and synthetic rubber, making combustion analysis significant for safety and efficiency.

2-Methylbutane Combustion

2-Methylbutane (\text{C}_5 \text{H}_{12}) is a branched hydrocarbon. It undergoes complete combustion to produce carbon dioxide and water.

• Reactants: 2-Methylbutane and oxygen
• Products: Carbon dioxide and water

The balanced equation is: $${\text{C}}_5{\text{H}}_{12}+8{\text{O}}_2\to 5{\text{CO}}_2+6{\text{H}}_2\text{O}$$
Ensuring each type of atom balances is vital.
2-Methylbutane is commonly found in gasoline, so studying its combustion helps optimize fuel efficiency and emissions in engines.