Question

Complete and balance each hydrocarbon combustion reaction. \begin{equation}\begin{array}{l}{\text { a. } \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}+\mathrm{O}_{2} \longrightarrow} \\ {\text { b. } \mathrm{CH}_{2}=\mathrm{CHCH}_{3}+\mathrm{O}_{2} \longrightarrow} \\\ {\text { c. } \mathrm{CH}=\mathrm{CCH}_{2} \mathrm{CH}_{3}+\mathrm{O}_{2} \longrightarrow}\end{array} \end{equation}

Short answer

The balanced equations are: (a) \( C_4H_{10} + 13/2 O_2 \longrightarrow 4 CO_2 + 5 H_2O \), (b) \( C_3H_6 + 9/2 O_2 \longrightarrow 3 CO_2 + 3 H_2O \), (c) \( C_4H_6 + 11/2 O_2 \longrightarrow 4 CO_2 + 3 H_2O \).

Step-by-step solution

Write the Products of the Combustion

In a hydrocarbon combustion reaction, the hydrocarbon reacts with oxygen to produce carbon dioxide (CO2) and water (H2O). So the products for each reaction will be CO2 and H2O.

Balance Carbon Atoms

Balance the number of carbon atoms in the products with the number of carbon atoms in the reactants. This is done by adjusting the coefficient in front of the carbon dioxide (CO2) to match the number of carbon atoms in each hydrocarbon.

Balance Hydrogen Atoms

Next, balance the hydrogen atoms. Adjust the number of water (H2O) molecules to have the same number of hydrogen atoms as there are in the reactants.

Balance Oxygen Atoms

Finally, balance the oxygen atoms. Since each molecule of CO2 has two oxygen atoms and each molecule of H2O has one, count the total number of oxygen atoms in the CO2 and H2O and adjust the coefficient in front of O2 to balance it.

Write the Balanced Equations

(a) \( C_4H_{10} + 13/2 O_2 \longrightarrow 4 CO_2 + 5 H_2O \)(b) \( C_3H_6 + 9/2 O_2 \longrightarrow 3 CO_2 + 3 H_2O \)(c) \( C_4H_6 + 11/2 O_2 \longrightarrow 4 CO_2 + 3 H_2O \)

Key concepts

Balancing Chemical Equations

Balancing chemical equations is critical in chemistry to ensure that there is an equal number of atoms for each element in the reactants and products. This practice adheres to the Law of Conservation of Mass, which states that matter cannot be created or destroyed in a chemical reaction.
To balance a chemical equation, one must first write the correct formulas for each reactant and product. Then, coefficients are placed before the formulas to adjust the number of atoms. The coefficients should be the lowest whole numbers that balance the atoms on both sides of the equation. Since oxygen atoms are often abundant in reactions like combustion, they are typically balanced last. And remember, subscripts should not be changed as they represent the fixed composition of a substance.
A helpful tip is to start by balancing atoms of elements that appear only once on each side of the equation and to leave the more complex molecules, often those with oxygen, for last. Patience and practice are key to mastering the balancing of chemical equations.

Stoichiometry

Stoichiometry is the quantitative relationship between reactants and products in a chemical reaction. It is grounded on the balanced chemical equation and allows for calculations of the amounts of substances consumed and produced. Stoichiometry is essential for determining reactant quantities and for predicting the yield of products, thereby playing a crucial role in chemical manufacturing and laboratory work.
To perform stoichiometric calculations, begin with a properly balanced chemical equation. Use the coefficients from this equation to convert between moles of one substance to moles of another. These coefficients represent the mole ratio of the reactants and products.

• To calculate the mass of a product, one would use the molar mass of the reactants.
• For volume measurements, the gas laws may be applied if the substances are gases.
• In concentration calculations, molarity (moles per liter) is often used.

Understanding stoichiometry is fundamental for precise scientific experiments, optimizing industrial processes, and even in everyday tasks such as cooking, where recipe ingredients are based on stoichiometric ratios.

Combustion Reactions

Combustion reactions are a type of exothermic chemical reaction where a substance combines with oxygen, releasing energy in the form of heat and light. Hydrocarbon combustion, which includes the burning of coal, natural gas, and petroleum, is a familiar example and forms the basis for much of the world's energy production.
In a typical hydrocarbon combustion reaction, the carbon (C) and hydrogen (H) in the hydrocarbon react with atmospheric oxygen (O2) to form carbon dioxide (CO2) and water (H2O). These reactions must be carefully balanced, as seen in the steps outlined in the provided exercise, to account for all atoms of carbon, hydrogen, and oxygen. It's critical to note the importance of balancing oxygen molecules last because they are involved in the formation of both CO2 and H2O.
Combustion reactions are vital for numerous applications beyond energy production, such as in automobile engines and in various industrial processes. They also play a significant role in environmental considerations, as incomplete combustion can lead to the release of pollutants like carbon monoxide (CO). This highlights the importance of understanding the reaction mechanism and ensuring complete combustion where possible.