Chapter 12- Alkanes

Question 1

What is the primary use for alkanes?

Answer 1

Use as Fuel

Question 2

What is the general formula for and alkane?

Answer 2

CnH2n+2

Question 3

What is the bond angle around each carbon in an alkane?

Answer 3

109.5

Question 4

True or False? You do not get free rotation around a sigma bond

Answer 4

False

Question 5

Why do longer chain alkanes have a higher boiling point than shorter ones?

Answer 5

Increased surface contact means more London Forces which means more energy is required to break them.

Question 6

Do branched alkanes have a higher or lower boiling point than unbranched alkanes?

Answer 6

Lower, as there is less surface contact.

Question 7

Why are alkanes unreactive?

Answer 7

They are saturated and non-polar molecules

Question 8

Write a balanced symbol equation for the reaction for Hexane burning.

Answer 8

C6H14 (l) + 9.5O2 (g) –> 6CO2 +7H20

Question 9

What is required to start a free radical substitution reaction?

Answer 9

UV Light

Question 10

What are the names of the 3 stages in the mechanism of free radical substitution?

Answer 10

Initiation, Propagation, Termination

Question 11

Write an equation for the initiation phase when a bromine molecule reacts with UV light.

Answer 11

Br2 –> 2Br*

Question 12

Write the 2 equations that would occur when a bromine radical reacts with a methane molecule.

Answer 12

Step 1: CH4+ Br* –> *CH3+ HBr

Step 2: CH3 + Br2 –> CH3Br + Br

Question 13

What 3 possible equations for the termination phase of bromine reacting with methane.

Answer 13

2Br* –> Br2
CH3*+ *CH3 –> C2H6
CH3 + Br –> CH3Br

Question 14

Describe what happens in terms of number of free radicals reacting and being produced for each stage of the mechanism.

Answer 14

Initiation- No Free Radicals –> 2 free radicals
Propagation- 1 Free Radical –> 1 free radical
Termination- 2 Free Radicals –> No free radicals