4.5 ALKANES AND ALKENES

Question 1

general formula of alkanes:

Answer 1

CnH2n+2

Question 2

names of the first five alkanes:

Answer 2

• methane CH4
• ethane C2H6
• propane C3H8
• butane C4H10
• pentane C5H12

Question 3

displayed formula:

Answer 3

drawn out showing the positions of every atom and every bond

Question 4

structural formula (butane example):

Answer 4

shows the structure of the molecule in one line
CH3CH2CH2CH3

Question 5

molecular formula (butane example):

Answer 5

shows only how many hydrogen and carbon atoms there are
C4H10

Question 6

empirical formula (butane example):

Answer 6

shows the simplest whole-number ratio of carbon to hydrogen

Question 7

what is a homologous series?

Answer 7

• similar chemical reactions
• trends in physical properties (boiling points, viscosity, colour)
• same general formula

Question 8

what is an isomer in alkanes?

Answer 8

molecules with the same molecular formula but a different structural formula

Question 9

complete combustion:

Answer 9

• alkane + oxygen —> carbon dioxide + water
• occurs when there is excess oxygen

Question 10

incomplete combustion:

Answer 10

• occurs when there isn’t enough oxygen
• produces carbon monoxide and soot
• releases less energy

Question 11

what does the combustion of alkanes/alkenes as fuels produce?

Answer 11

• carbon dioxide (greenhouse gas)
• nitrogen oxide- forms when nitrogen in the air combusts (acid rain)
• sulphur dioxide- forms when sulphur impurities in the fuel combusts (acid rain)

Question 12

how do alkanes react with halogens?

Answer 12

by swapping one hydrogen atom for one halogen atom

Question 13

details for alkanes reacting with halogens:

Answer 13

• substitution reaction because the H swaps with the Br
• requires UV light because the alkane is unreactive

Question 14

are alkanes and alkenes hydrocarbons?

Answer 14

yes

Question 15

general formula for alkenes:

Answer 15

CnH2n

Question 16

first four alkenes:

Answer 16

• ethene C2H4
• propene C3H6
• butene C4H8
• pentene C5H10

Question 17

difference between alkanes and alkenes:

Answer 17

• alkenes have one C=C double bond in their carbon chain
• in the structural formula this is sometimes shown as “=”

Question 18

what are alkenes?

Answer 18

• homologous series of organic molecules
• family of molecules which have:
  1. similar chemical reactions
  2. trends in physical properties (colour, boiling points, viscosity)
  3. same general formula

Question 19

do alkenes have isomers?

Answer 19

• yes
• they can differ in more than one way (unlike alkanes)

Question 20

how can alkenes differ in two ways in isomers?

Answer 20

• branch off of the carbon chain
• the position of the C=C bond

Question 21

are alkenes saturated or unsaturated?

Answer 21

• unsaturated
• due to their C=C bond

Question 22

are alkanes saturated or unsaturated?

Answer 22

• saturated
• because their is no C=C bond

Question 23

how do alkenes react with bromine?

Answer 23

• break the C=C bonds and add bromine

Question 24

details for alkenes reacting with bromine:

Answer 24

• addition reaction- adding bromine atoms to alkene
• happens without UV light because alkenes are more reactive than alkanes
• works with pure bromine liquid or bromine water (which is orange)
• mixture turns orange to colourless because the bromine is used up during the reaction