Question

Write a balanced equation for the complete combustion for each of the following: (a) methane (b) propane (c) hexane (d) octane

Short answer

The balanced equations are: (a) CH₄ + 2O₂ → CO₂ + 2H₂O (b) C₃H₈ + 5O₂ → 3CO₂ + 4H₂O (c) 2C₆H₁₄ + 19O₂ → 12CO₂ + 14H₂O (d) 2C₈H₁₈ + 25O₂ → 16CO₂ + 18H₂O.

Step-by-step solution

Understand Combustion Process

Combustion is a chemical reaction where a fuel reacts with oxygen to produce carbon dioxide and water. In the case of hydrocarbons like methane, propane, hexane, and octane, the general form of the combustion reaction is: \[ \text{C}_x\text{H}_y + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} \] Our task is to balance this equation for each given hydrocarbon.

Write Methane Combustion Equation

Methane (CH₄) is the simplest hydrocarbon. The unbalanced combustion equation is: \[ \text{CH}_4 + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} \] Balancing the equation, we get: \[ \text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O} \]

Write Propane Combustion Equation

Propane (C₃H₈) combustion equation starts as: \[ \text{C}_3\text{H}_8 + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} \] Balancing the equation, we have: \[ \text{C}_3\text{H}_8 + 5\text{O}_2 \rightarrow 3\text{CO}_2 + 4\text{H}_2\text{O} \]

Write Hexane Combustion Equation

Hexane (C₆H₁₄) combustion involves the initial equation: \[ \text{C}_6\text{H}_{14} + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} \] Balancing it results in: \[ \text{C}_6\text{H}_{14} + \frac{19}{2}\text{O}_2 \rightarrow 6\text{CO}_2 + 7\text{H}_2\text{O} \] A more common form using integers is: \[ 2\text{C}_6\text{H}_{14} + 19\text{O}_2 \rightarrow 12\text{CO}_2 + 14\text{H}_2\text{O} \]

Write Octane Combustion Equation

Octane (C₈H₁₈), commonly used in gasoline, starts with: \[ \text{C}_8\text{H}_{18} + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} \] Balancing gives: \[ \text{C}_8\text{H}_{18} + \frac{25}{2}\text{O}_2 \rightarrow 8\text{CO}_2 + 9\text{H}_2\text{O} \] Or using whole numbers: \[ 2\text{C}_8\text{H}_{18} + 25\text{O}_2 \rightarrow 16\text{CO}_2 + 18\text{H}_2\text{O} \]

Key concepts

Chemical Equation Balancing

Balancing chemical equations is a fundamental skill in chemistry, crucial to understanding how substances react with one another. Each side of the equation must have equal numbers of each type of atom. This is based on the law of conservation of mass, which states that mass cannot be created or destroyed in a chemical reaction.
For balancing, identify the number of atoms of each element on both sides of the equation. Adjust coefficients (the numbers before molecules, not the subscripts in the formulas) to get the same number of each type of atom on each side.
For example, in the combustion of propane: \(\text{C}_3\text{H}_8 + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} \)

• Start by balancing carbons: 3 carbon atoms in propane require 3 CO₂ molecules.
• Next, balance hydrogen: 8 hydrogen atoms in propane require 4 H₂O molecules.
• Balance oxygen last: there are 10 oxygen atoms needed (3x2 from CO₂ and 4x1 from H₂O), so 5 O₂ molecules are needed.

This systematic approach ensures each element is balanced step by step.

Hydrocarbons

Hydrocarbons are organic compounds composed entirely of hydrogen and carbon. They can be classified into alkanes, alkenes, alkynes, and aromatic hydrocarbons.

Hydrocarbons are central to energy production because they are the main components of fuels like gasoline. Different hydrocarbons have varying structures:

• Methane (CH₄) is the simplest hydrocarbon, consisting of one carbon atom surrounded by four hydrogen atoms.
• Propane (C₃H₈) has a three-carbon chain.
• Hexane (C₆H₁₄) and octane (C₈H₁₈) are longer-chain hydrocarbons found in gasoline.

These hydrocarbons burn in oxygen to release energy, carbon dioxide, and water—a process utilized in engines and heating. Understanding the structure helps predict their behavior in reactions.

Chemical Reactions

Chemical reactions are processes where substances (reactants) are transformed into new substances (products). These reactions can be simple, involving just one step, or complex, involving several intermediate steps. Combustion reactions are a type of exothermic chemical reaction.
In a combustion reaction involving hydrocarbons, oxygen acts as a reactant along with the hydrocarbon, producing carbon dioxide and water as products:
For hexane: \(\text{C}_6\text{H}_{14} + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} \)

• Hydrocarbons combust completely in oxygen, producing energy, carbon dioxide, and water.
• The reaction is exothermic, meaning it releases heat into the surroundings.
• This property makes hydrocarbons advantageous as fuels.

Such reactions are vital for energy production in many industrial and domestic applications. Understanding them helps in optimizing energy use and addressing environmental concerns like CO₂ emissions.