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OCR A-Level Chemistry: Chapter 12 -Alkanes

Chemistry19 CardsCreated 2 months ago

This flashcard set covers the essential properties of alkanes, including their primary use as fuels, their general molecular formula, and the nature of covalent bonding. It introduces sigma bonds as the fundamental bonding type in these saturated hydrocarbons.

What is the main use of alkanes?

Fuel

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Key Terms

Term
Definition

What is the main use of alkanes?

Fuel

What is the general formula of alkanes?

CnH2n+2

What kind of covalent bonds are formed in alkanes?

Sigma bonds

What is a sigma bond?

The overlap of two orbitals

How are alkanes separated?

Fractional distillation

How does chain length effect boiling point?

Longer chain length raises boiling point

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TermDefinition

What is the main use of alkanes?

Fuel

What is the general formula of alkanes?

CnH2n+2

What kind of covalent bonds are formed in alkanes?

Sigma bonds

What is a sigma bond?

The overlap of two orbitals

How are alkanes separated?

Fractional distillation

How does chain length effect boiling point?

Longer chain length raises boiling point

Why does chain length have that effect on boiling point?

Increased chain length
Greater surface area of contact
Stronger London forces

What is the effect of branching on boiling point?

Lowers boiling point

Why does branching have that effect on boiling point?

More branching
Less surface area of contact
Weaker London forces

What are the reasons for alkanes being fairly unreactive?

C-C and C-H sigma bonds are strong
C-C bonds are non polar
Similar electronegativity of C and H


What is the combustion reaction of an alkane in words?

Alkane + oxygen -> water + carbon dioxide

What is complete combustion?

Alkanes burn completely to produce carbon dioxide and water.

What are the two potential products from incomplete combustion of alkanes?

Carbon monoxide

Carbon

What is the name of the mechanism for bromination of alkanes?

Free radical substitution

What are the three stages of radical substitution?

Initiation
Propagation
Termination

Describe the initiation stage of radical substitution

Covalent bond in a bromine molecule is broken by homolytic fission.
Energy provided by UV radiation.
Br-Br -> Br* + Br*

Describe the propagation stage of radical substitution

Two propagation steps:
Step 1 - CH4 + Br* -> *CH3 + HBr
Step 2 - CH3 + Br2 -> CH3Br + Br

Describe the termination stage of radical substitution

Two radicals collide forming a molecule with all electrons paired.
Br* + Br* -> Br2
*CH3 + *CH3 -> C2H6
CH3 + Br -> CH3Br

What can occur after a radical substitution reaction?

Further substitution