Question

Complete and balance each of the following chemical equations. a. \(\mathrm{C}_{8} \mathrm{H}_{18}(l)+\mathrm{O}_{2}(g) \rightarrow\) b. \(\mathrm{CH}_{3} \mathrm{Cl}(l)+\mathrm{Cl}_{2}(g) \rightarrow\) c. \(\mathrm{CHCl}_{3}(l)+\mathrm{Cl}_{2}(g) \rightarrow\)

Short answer

a. \(C_8H_{18} + 12.5O_2 \rightarrow 8CO_2 + 9H_2O\) b. \(\mathrm{CH}_{3} \mathrm{Cl}(l)+\frac{1}{2}\mathrm{Cl}_{2}(g) \rightarrow \mathrm{CH}_{2}\mathrm{Cl}_{2}(l)\) c. \(\mathrm{CHCl}_{3}(l) + \frac{1}{2} \mathrm{Cl}_{2}(g) \rightarrow \mathrm{CCl}_4(l)\)

Step-by-step solution

1. Identifying the products of the reaction

The given reaction is between octane (an alkane hydrocarbon) and oxygen. This type of reaction is called combustion. In a combustion reaction, the products formed are carbon dioxide (CO₂) and water (H₂O). Now, the complete unbalanced reaction looks like this: \(\mathrm{C}_{8} \mathrm{H}_{18}(l)+\mathrm{O}_{2}(g) \rightarrow \mathrm{CO}_{2}(g)+\mathrm{H}_{2}\mathrm{O}(l)\)

2. Balancing the chemical equation

First, we balance the carbon atoms: \(C_8H_{18} + O_2 \rightarrow 8CO_2 + H_2O\) Next, we balance the hydrogen atoms: \(C_8H_{18} + O_2 \rightarrow 8CO_2 + 9H_2O\) Lastly, we balance the oxygen atoms: \(C_8H_{18} + 12.5O_2 \rightarrow 8CO_2 + 9H_2O\) b. \(\mathrm{CH}_{3} \mathrm{Cl}(l)+\mathrm{Cl}_{2}(g) \rightarrow\)

1. Identifying the products of the reaction

The given reaction is between chloromethane (CH3Cl) and chlorine gas (Cl2). This type of reaction results in free radical chlorination, forming dichloromethane (CH2Cl2). Now, the complete unbalanced reaction looks like this: \(\mathrm{CH}_{3} \mathrm{Cl}(l)+\mathrm{Cl}_{2}(g) \rightarrow \mathrm{CH}_{2}\mathrm{Cl}_{2}(l)\)

2. Balancing the chemical equation

To balance the equation, we adjust the coefficients: \(\mathrm{CH}_{3} \mathrm{Cl}(l)+\frac{1}{2}\mathrm{Cl}_{2}(g) \rightarrow \mathrm{CH}_{2}\mathrm{Cl}_{2}(l)\) c. \(\mathrm{CHCl}_{3}(l)+\mathrm{Cl}_{2}(g) \rightarrow\)

1. Identifying the products of the reaction

The given reaction is between chloroform (CHCl3) and chlorine gas (Cl2). This is another free radical chlorination reaction, forming carbon tetrachloride (CCl4). Now, the complete unbalanced reaction looks like this: \(\mathrm{CHCl}_{3}(l)+\mathrm{Cl}_{2}(g) \rightarrow \mathrm{CCl}_{4}(l)\)

2. Balancing the chemical equation

To balance the equation, we adjust the coefficients: \(\mathrm{CHCl}_{3}(l) + \frac{1}{2} \mathrm{Cl}_{2}(g) \rightarrow \mathrm{CCl}_4(l)\)

Key concepts

Combustion Reactions

Combustion reactions are a type of chemical reaction where a substance combines with oxygen and releases energy in the form of heat and light. They are vital in everyday life as they provide energy for heating, transportation, and electricity generation. A common example is the burning of hydrocarbons, such as octane found in gasoline, which produces carbon dioxide and water as products.

In the case of octane (\(\mathrm{C}_{8} \mathrm{H}_{18}\)), the combustion reaction involves reacting with oxygen (\(\mathrm{O}_{2}\)) to form carbon dioxide (\(\mathrm{CO}_{2}\)) and water (\(\mathrm{H}_{2}\mathrm{O}\)). The balanced equation for this reaction ensures compliance with the law of conservation of mass, meaning the number of each type of atom in the reactants must equal the number in the products.

• The general formula for the combustion of a hydrocarbon is: \[\mathrm{C}_x \mathrm{H}_y + \mathrm{O}_2 \rightarrow \mathrm{CO}_2 + \mathrm{H}_2\mathrm{O}\]
• The balancing sequence typically begins with carbon, followed by hydrogen, and finally oxygen.
• Keep in mind that oxygen is often required in fractions, and it is commonplace to multiply all coefficients to convert them to whole numbers.

Hydrocarbons

Hydrocarbons are organic compounds composed solely of carbon and hydrogen atoms. They serve as the primary constituent of fuels such as gasoline, diesel, and natural gas. Hydrocarbons are classified into different types based on their structure, such as alkanes, alkenes, and alkynes. In the context of the provided problems, we focus mainly on alkanes like octane, and on chlorinated hydrocarbons like chloromethane and chloroform.

Key characteristics of hydrocarbons include:

• Alkanes, also known as paraffins, are saturated hydrocarbons with single bonds.
• Alkenes and alkynes, also called olefins and acetylenes, are unsaturated hydrocarbons with double and triple bonds, respectively.
• Hydrocarbons are flammable and serve as significant sources of energy through combustion.

Hydrocarbons often undergo chemical reactions including combustion, substitution, and addition reactions, leading to the formation of various compounds utilized in industrial and everyday applications.

Free Radical Chlorination

Free radical chlorination is a chemical reaction involving the substitution of a hydrogen atom in a hydrocarbon with a chlorine atom, facilitated by the presence of free radicals. This reaction proceeds through a chain mechanism consisting of initiation, propagation, and termination steps.

In free radical chlorination, a chlorine molecule (\(\mathrm{Cl}_{2}\)) is exposed to ultraviolet light or heat, causing it to dissociate into two chlorine radicals. These radicals are highly reactive and can abstract hydrogen atoms from hydrocarbons, forming hydrochloric acid (\(\mathrm{HCl}\)) and leaving an organic radical that subsequently reacts with another \(\mathrm{Cl}_{2}\) molecule to form a chlorinated product.

• Initiation: \(\mathrm{Cl}_{2} \xrightarrow{hv} 2 \mathrm{Cl}^\cdot\) (formation of chlorine radicals)
• Propagation: Ongoing reactions that form more radicals, stabilizing chain reactions.
• Termination: Combination of any two radicals to form stable products.

The process is exemplified by chloromethane and chloroform reactions, resulting in the formation of dichloromethane and carbon tetrachloride, respectively. These chlorinated compounds find use in solvent applications, chemical synthesis, and even as precursors in various industrial processes.