Question

Write a balanced chemical equation for the complete combustion of benzene.

Short answer

The balanced chemical equation is \( 2C_6H_6 + 15O_2 \rightarrow 12CO_2 + 6H_2O \).

Step-by-step solution

Identify the Reactants and Products

The problem involves the complete combustion of benzene, which is a hydrocarbon with the chemical formula \( C_6H_6 \). In complete combustion, benzene reacts with oxygen \( O_2 \) to produce carbon dioxide \( CO_2 \) and water \( H_2O \).

Write an Unbalanced Equation

Write the initial chemical equation representing the combustion:\[C_6H_6 + O_2 ightarrow CO_2 + H_2O\]This equation shows the frameworks of the reactants turning into products, but it is not yet balanced in terms of the number of atoms.

Balance the Carbon Atoms

Benzene has 6 carbon atoms, so you will need 6 carbon dioxide molecules to balance the carbon atoms. Adjust the equation: \[C_6H_6 + O_2 ightarrow 6CO_2 + H_2O\]

Balance the Hydrogen Atoms

Benzene has 6 hydrogen atoms, requiring 3 water molecules to supply the necessary 6 hydrogen atoms. Update the equation:\[C_6H_6 + O_2 ightarrow 6CO_2 + 3H_2O\]

Balance the Oxygen Atoms

Count the total oxygen atoms needed on the product side: 12 from \( 6CO_2 \) and 3 from \( 3H_2O \), making 15 oxygen atoms. Since each \( O_2 \) molecule provides 2 oxygen atoms, you need \( \frac{15}{2} = 7.5 \) or 15/2 oxygen molecules. Set the balanced equation:\[C_6H_6 + \frac{15}{2}O_2 ightarrow 6CO_2 + 3H_2O\]

Clear Fractional Coefficients

To eliminate the fraction, multiply all coefficients by 2 to get whole numbers:\[2C_6H_6 + 15O_2 ightarrow 12CO_2 + 6H_2O\]

Key concepts

Combustion Reaction

A combustion reaction is a chemical process where a substance combines with oxygen and releases energy in the form of heat and light. When we talk about the combustion of hydrocarbons like benzene, the process produces carbon dioxide and water. This type of reaction is essential for understanding how fuels burn, such as those we use for cars or heating.
In a combustion reaction:

• The reactants include a fuel (often a hydrocarbon) and oxygen.
• The products are typically carbon dioxide and water, provided the combustion is complete.
• Complete combustion happens when there is enough oxygen to allow the fuel to become fully oxidized.

It's crucial to ensure adequate oxygen supply for complete combustion to avoid the production of carbon monoxide, a potentially dangerous product of incomplete combustion. Understanding the fundamentals of combustion reactions can help us in various fields, from energy production to environmental science.

Balancing Equations

Balancing chemical equations is a critical skill in chemistry that involves making sure the same number of each type of atom appears on both sides of the equation. This principle stems from the Law of Conservation of Mass, which asserts that mass cannot be created or destroyed in a chemical reaction.
To balance a chemical equation:

• Write down the unbalanced equation.
• Count the number of atoms for each element on both sides of the equation.
• Adjust the coefficients (the numbers before molecules) to obtain equal numbers of each kind of atom on each side.
• Ensure the simplest whole-number ratio of coefficients if necessary.

In our benzene combustion example, we balance carbon, hydrogen, and oxygen atoms separately to follow this law.
This task is like solving a puzzle where every piece needs to fit perfectly, highlighting the beauty of chemistry's logical and mathematical elements. Balancing equations ensures that we accurately represent chemical reactions and predict how much of each substance we need and produce.

Stoichiometry

Stoichiometry involves the calculation of reactants and products in chemical reactions using a balanced equation. It's like the bookkeeping system of chemistry that helps us understand the proportions in which chemicals react.
Here's how stoichiometry works:

• Start with a balanced chemical equation.
• Use the coefficients from the equation to determine the molar ratios between reactants and products.
• Calculate the amount of one or more substances in moles using these ratios.

Stoichiometry answers questions like how much oxygen is needed to completely combust a given amount of benzene or how much product can be expected from this combustion.
In our example:

• The balanced equation tells us that 2 moles of benzene react with 15 moles of oxygen to produce 12 moles of carbon dioxide and 6 moles of water.

By understanding stoichiometry, students can not only predict the outcomes of reactions but also work efficiently in labs to avoid waste and ensure precise results. This concept is foundational to mastering chemistry and observing its applications in real-world situations like industrial manufacturing or pharmaceuticals.