Alkanes

Question 1

What is the general formula of an alkane?

Answer 1

CnH(2n+2)

Question 2

What is a sigma bond?

Answer 2

Overlap of two s orbitals

Question 3

How is the shape determined in alkanes? (3)

Answer 3

• Carbon atoms are surrounded by 4 electron pairs
• Repulsion between these electrons create a tetrahedral shape
• Each bond angle is approximately 109.5°

Question 4

What is the effect of chain length on boiling point? (5)

Answer 4

• As chain length increases, surface area increases
• More surface contact with other molecules
• More London Forces
• More energy required to overcome the inter-molecular forces
• Higher boiling point

Question 5

What is the effect of branching on boiling point? (4)

Answer 5

• More branches mean less surface contact with other molecules
• Less London Forces
• Less energy needed to overcome the inter-molecular forces
• Lower boiling point

Question 6

What products are formed in the complete combustion of alkanes? (2)

Answer 6

• Carbon dioxide

- Water

Question 7

What products may form in the incomplete combustion of alkanes?

Answer 7

Carbon Monoxide

Question 8

What are the conditions needed for the halogenation of alkanes? What are the products? (2)

Answer 8

Condition = UV Light
Products = Haloalkane and Hydrogen Halide

Question 9

What are the three stages of free radical substitution?

Answer 9

Initiation, propagation and termination

Question 10

What occurs in the initiation step for the bromination of alkenes? (1)

Answer 10

Br2 -> 2BR*

Question 11

What happens in propagation during the bromination of alkanes? (2)

Answer 11

CH4 + Br* -> *CH3 + HBr

CH3 + Br2 -> CH3Br + Br

Question 12

What happens in termination during the bromination of alkanes? (3)

Answer 12

Br* + Br* -> Br2

• CH3 + *CH3 -> C2H6
• CH3 + Br* -> CH3Br