6.3.2 Reactions of Alkanes

• What is the defining characteristic of alkanes?

  Single covalent bonds
• Alkanes are generally unreactive due to the presence of strong, non-polar single covalent bonds.
• What are the two types of combustion that alkanes can undergo?

  Complete and incomplete
• Steps in the complete combustion of alkanes

  1️⃣ Sufficient oxygen is present

  2️⃣ Alkanes react with oxygen

  3️⃣ Carbon dioxide and water are produced
• The products of complete combustion of alkanes are carbon dioxide and water
• What are the products of incomplete combustion of alkanes?

  Carbon monoxide, carbon, water
• Alkanes are saturated hydrocarbons connected by single covalent bonds.
• Alkanes are unreactive because their single covalent bonds are strong and non-polar
• Under what conditions does incomplete combustion of alkanes occur?

  Insufficient oxygen
• In complete combustion of methane, the products are carbon dioxide and water
• The products of incomplete combustion include carbon monoxide, carbon, and water
• Match the combustion type with its oxygen availability and products:

  Complete Combustion ↔️ Sufficient oxygen, $CO_{2}$, $H_{2}O$

  Incomplete Combustion ↔️ Insufficient oxygen, $CO$, $C$, $H_{2}O$
• Steps involved in the complete combustion of alkanes:

  1️⃣ Alkane reacts with oxygen

  2️⃣ Heat and light are released

  3️⃣ Carbon dioxide and water are produced
• The general equation for complete combustion of alkanes is C_{n}H_{2n + 2} + \frac{3n + 1}{2}O_{2} \rightarrow nCO_{2} + (n + 1)H_{2}O
• Incomplete combustion of alkanes produces toxic carbon monoxide.
• Substitution reactions in alkanes require UV light or heat
• The free radical mechanism for substitution reactions involves three main steps.
• Steps in the free radical mechanism for substitution reactions:

  1️⃣ Initiation: Formation of free radicals

  2️⃣ Propagation: Free radicals react with alkanes

  3️⃣ Termination: Free radicals combine to form stable molecules
• The chlorination of methane is an example of a substitution reaction in alkanes that produces CH_{3}Cl
• During initiation, UV light breaks the bond in $Cl_{2}$ to form two radicals
• In propagation, a chlorine radical abstracts a hydrogen atom from methane.
• The chlorination of methane follows the free radical mechanism
• Cracking of alkanes is used to break larger molecules into smaller, more useful hydrocarbons
• Thermal cracking and catalytic cracking are two methods used in the cracking of alkanes.
• Cracking decane produces octane and ethene
• Match the characteristic with its description in alkanes:

  Saturated Hydrocarbons ↔️ Compounds with single covalent bonds between carbon atoms

  General Formula ↔️ $C_{n}H_{2n + 2}$

  Example ↔️ $CH_{4}$
• Alkanes have limited reactivity due to strong, non-polar covalent bonds.
• What are alkanes composed of?

  Carbon and hydrogen atoms
• Alkanes are saturated hydrocarbons
• The general formula for alkanes is $C_{n}H_{2n + 2}$.
• What is the simplest alkane with one carbon atom?

  Methane
• Alkanes have limited reactivity due to the strong and non-polar single covalent bonds between carbon and hydrogen atoms.
• What type of bonds contribute to the low reactivity of alkanes?

  Strong and non-polar
• Complete combustion of alkanes occurs with sufficient oxygen
• The general equation for complete combustion of alkanes is C_{n}H_{2n + 2} + \frac{3n + 1}{2}O_{2} \rightarrow nCO_{2} + (n + 1)H_{2}O</latex>.
• What are the products of the complete combustion of methane?

  Carbon dioxide and water
• Incomplete combustion of alkanes occurs with insufficient oxygen
• What are the products of the incomplete combustion of alkanes?

  Carbon monoxide, carbon, water
• The example equation for incomplete combustion of methane is 2CH_{4} + 3O_{2} \rightarrow 2CO + 4H_{2}O</latex>.
• Steps in the free radical mechanism of substitution reactions in alkanes

  1️⃣ Initiation

  2️⃣ Propagation

  3️⃣ Termination