Hydrocarbons Continued

Question 1

Alkanes are chemically inert, what does that mean

Answer 1

They do not react easily

Question 2

What are 3 reactions and uses of alkanes

Answer 2

1. ) cracking
2. ) free radical substitution
3. ) free radical oxidation (burn)

Question 3

Describe cracking of alkanes

Answer 3

Large hydrocarbon molecules can be cracked into smaller more useful molecules (eg petrol). High temperature, high pressure and special catalysts are needed (atypical reaction condition)

Question 4

Describe free radical substitution of alkanes

Answer 4

To form halogenoalkanes

Question 5

Describe radical oxidation of alkanes

Answer 5

They burn (used as fuels)

Question 6

What are the physical properties of alkanes

3 things

Answer 6

1. ) No strong intermolecular forces (van der Waals only) therefore low melting and boiling points
2. ) branching decreases the boiling point due to decreased van der Waals forces (poorer molecular packing).
3. ) non-polar- so soluble in non-polar solvents and insoluble in water

Question 7

What are alkenes

Answer 7

Alkenes contain only hydrogen and carbon, but contain double bonds (not all carbon atoms are saturated with hydrogen)

Question 8

What is the general formula of acyclic alkenes

Answer 8

CnH2n

Question 9

What shape are unsaturated hydrocarbon atoms

Answer 9

Trigonal planar

Question 10

How do you name alkenes

Answer 10

Same rules as alkenes but use suffix -ene. Position of the doubly bond must be clear in the name.

Question 11

What do you need to note she naming branched alkenes

Answer 11

They are always names with the alkene as a part of the parent chain even if it means the parent chain isn’t the longest branch

Question 12

What is geometric isomerism

Answer 12

Compounds all have the same bonds but in a different arrangement. Some of the carbon atoms are unsaturated

Question 13

What prefer trans arrangement

Answer 13

Larger molecules

Question 14

How are trans and cis geometric isomers different

Answer 14

They have very different chemical and physical properties due to their different surface areas. The different surface areas means very different van dee Waals forces. Trans isomers as more stable

Question 15

What are the two types of geometric isomers

Answer 15

Trans and cis

Question 16

What are double bond equivalents a measure of

Answer 16

The unsaturation of a molecule

Question 17

What formula is used to calculate double bond equivalents

Answer 17

DBE= (2C + 2 - H + N - Hal)/ 2

Where C, N and Hal are the number of carbon, nitrogen and halogen atoms respectively

Question 18

Is C4H16 feasible

Answer 18

No.
DBE = (2x4 + 2 -16)/2 = -3
DBE must be 0 or greater

Question 19

What must DBE be to make a molecule feasible

Answer 19

0 or greater and a whole number

Question 20

Are alkenes more reactive than alkanes

Answer 20

Yes, the double bond of alkenes are much more reactive than alkanes

Question 21

What are the main reactions of alkenes

Answer 21

1. ) hydrogenation
2. ) addition reactions
3. ) polymerisation

Question 22

Describe hydrogenation of alkenes

Answer 22

The addition of hydrogen to form alkanes

Question 23

Describe addition reactions of alkenes

Answer 23

Other addition reactions (apart from hydrogenation) such as with halogens or water