Question

Write a balanced equation for the complete combustion of each of the following: a. heptane \(\mathbf{b} . \mathrm{HC} \equiv \mathrm{C}-\mathrm{CH}_{2}-\mathrm{CH}_{3}\) c. 2 -methylpropane d. \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{3}\)

Short answer

a) \(\text{C}_7\text{H}_{16} + 11O_2 \rightarrow 7CO_2 + 8H_2O\)b) \(\text{C}_3\text{H}_4 + 4O_2 \rightarrow 3CO_2 + 2H_2O\)c) \(\text{C}_4\text{H}_{10} + 6.5O_2 \rightarrow 4CO_2 + 5H_2O\)d) \(\text{C}_4\text{H}_{10} + 6.5O_2 \rightarrow 4CO_2 + 5H_2O\).

Step-by-step solution

- Identify the chemical formulas

Determine the chemical formula for each compound.(a) Heptane: \(\text{C}_7\text{H}_{16}\)(b) Propyne: \(\text{C}_3\text{H}_4\)(c) 2-Methylpropane: \(\text{C}_4\text{H}_{10}\)(d) Butane: \(\text{C}_4\text{H}_{10}\)

- Write the general combustion reaction

Write the general form of the combustion reaction for a hydrocarbon: \(\text{C}_x\text{H}_y + O_2 \rightarrow CO_2 + H_2O\).

- Balance the equation for heptane (C_7H_{16})

Start by writing the unbalanced equation: \(\text{C}_7\text{H}_{16} + O_2 \rightarrow CO_2 + H_2O\)Balance carbon (C): \(\text{C}_7\text{H}_{16} + O_2 \rightarrow 7CO_2 + H_2O\)Balance hydrogen (H): \(\text{C}_7\text{H}_{16} + O_2 \rightarrow 7CO_2 + 8H_2O\)Balance oxygen (O): \(\text{C}_7\text{H}_{16} + 11O_2 \rightarrow 7CO_2 + 8H_2O\).

- Balance the equation for propyne (C_3H_4)

Write the unbalanced equation: \(\text{C}_3\text{H}_4 + O_2 \rightarrow CO_2 + H_2O\)Balance carbon (C): \(\text{C}_3\text{H}_4 + O_2 \rightarrow 3CO_2 + H_2O\)Balance hydrogen (H): \(\text{C}_3\text{H}_4 + O_2 \rightarrow 3CO_2 + 2H_2O\)Balance oxygen (O): \(\text{C}_3\text{H}_4 + 4O_2 \rightarrow 3CO_2 + 2H_2O\).

- Balance the equation for 2-methylpropane (C_4H_{10})

Write the unbalanced equation: \(\text{C}_4\text{H}_{10} + O_2 \rightarrow CO_2 + H_2O\)Balance carbon (C): \(\text{C}_4\text{H}_{10} + O_2 \rightarrow 4CO_2 + H_2O\)Balance hydrogen (H): \(\text{C}_4\text{H}_{10} + O_2 \rightarrow 4CO_2 + 5H_2O\)Balance oxygen (O): \(\text{C}_4\text{H}_{10} + 6.5O_2 \rightarrow 4CO_2 + 5H_2O\).

- Balance the equation for butane (C_4H_{10})

Write the unbalanced equation: \(\text{C}_4\text{H}_{10} + O_2 \rightarrow CO_2 + H_2O\)Balance carbon (C): \(\text{C}_4\text{H}_{10} + O_2 \rightarrow 4CO_2 + H_2O\)Balance hydrogen (H): \(\text{C}_4\text{H}_{10} + O_2 \rightarrow 4CO_2 + 5H_2O\)Balance oxygen (O): \(\text{C}_4\text{H}_{10} + 6.5O_2 \rightarrow 4CO_2 + 5H_2O\).

Key concepts

Combustion Reactions

Combustion reactions are an essential part of chemistry. They involve a substance reacting with oxygen to produce heat and light. In many cases, the substance being burned is a hydrocarbon (a compound made of hydrogen and carbon atoms). The general form of a combustion reaction for hydrocarbons is: \ \(\text{C}_x\text{H}_y + O_2 \rightarrow CO_2 + H_2O\). This means a hydrocarbon reacts with oxygen to produce carbon dioxide (\(CO_2\)) and water (\(H_2O\)).
Combustion reactions are crucial in our daily lives, from heating homes to powering vehicles. Understanding them helps us see how energy is harnessed from chemical reactions.

Stoichiometry

Stoichiometry is the calculation of reactants and products in chemical reactions. It helps chemists determine the precise amounts of substances needed or produced in a reaction. The balanced chemical equation provides the mole ratio of reactants and products, which is essential for these calculations.
For example, in the combustion of heptane: \ \(\text{C}_7\text{H}_{16} + 11O_2 \rightarrow 7CO_2 + 8H_2O\). Here, the stoichiometry tells us that one mole of heptane reacts with eleven moles of oxygen to produce seven moles of carbon dioxide and eight moles of water.
By understanding stoichiometry, students can predict the quantities of reactants needed and products formed in any given reaction.

Hydrocarbons

Hydrocarbons are organic compounds consisting entirely of hydrogen and carbon. They are classified based on the types of bonds between carbon atoms. There are three main types: alkanes (single bonds), alkenes (one or more double bonds), and alkynes (one or more triple bonds).
Examples from the exercise include:

• Heptane: an alkane (\(\text{C}_7\text{H}_{16}\))
• Propyne: an alkyne (\(\text{C}_3\text{H}_4\))
• 2-Methylpropane: an alkane (\(\text{C}_4\text{H}_{10}\))
• Butane: an alkane (\(\text{C}_4\text{H}_{10}\))

Hydrocarbons are the primary fuels used in combustion engines. Learning about their properties and reactions is fundamental in both organic chemistry and everyday applications.

Balancing Chemical Equations

Balancing chemical equations is crucial to ensure that the law of conservation of mass is obeyed. This law states that mass cannot be created or destroyed in a chemical reaction.
To balance a chemical equation, follow these steps:

1. Write down the unbalanced equation.
2. Count the atoms of each element on both sides of the equation.
3. Add coefficients (numbers in front of molecules) to balance the atoms for each element.

For example, in the combustion of heptane: \ \(\text{C}_7\text{H}_{16} + 11O_2 \rightarrow 7CO_2 + 8H_2O\). Initially, the equation might not be balanced. By adjusting the coefficients, we ensure both sides have the same number of each type of atom.
Practicing this skill helps students understand the quantitative relationships in chemical reactions, which is essential for solving stoichiometric problems.

Organic Chemistry

Organic chemistry is the branch of chemistry that studies carbon-containing compounds. These compounds include a vast range of molecules, from simple hydrocarbons to complex biomolecules.
One core area in organic chemistry is studying reactions involving hydrocarbons. Combustion is a typical reaction, especially for alkanes, alkenes, and alkynes. Each type of hydrocarbon has unique properties and reactivities.
Understanding organic chemistry is key to many scientific and industrial fields. For instance, it plays a crucial role in pharmaceuticals, petrochemicals, and materials science.
By exploring exercises like balancing combustion reactions, students build a strong foundation in organic chemistry principles and applications.