2. alkanes

Question 1

general formula

Answer 1

Cn H2n+2

Question 2

cycloalkane general formula

Answer 2

CN H2n

Question 3

what shape are alkane molecules

Answer 3

tetrahedral around each C

Question 4

why are alkane molecules tetrahedral

Answer 4

each C atom has 4 pairs of bonding electrons
repel each other equally
each bond angle is 109.5

Question 5

what does the bpt of an alkane depend on

Answer 5

size and shape

Question 6

bpt for

1. small alkanes
2. large alkanes

Answer 6

1. low bpt. gases a room temp and pressure

2. high bpt. liquids at room temp and pressure

Question 7

bpt explained in alkanes

Answer 7

1. alkanes have covalent bonds inside molecules. between molecules there are LDF which hold them together
2. longer C chain, stronger LDF (more surface contact and more electrons to interact )
3. more energy needed to overcome LDF = higher bpt

Question 8

why does a branched alkane have a lower bpt than straight chained isomer

Answer 8

branched alkanes cant pack closely together. have smaller molecular surface area
LDS reduced

Question 9

alkanes burn completely in

Answer 9

oxygen

Question 10

if you burn alkanes with oxygen you get

what kind of reaction is this

Answer 10

CO2 and H2O

combustion

Question 11

why do smaller alkanes combust/burn more easily

Answer 11

they turn into gases more easily

combustion reactions happen between gases.

Question 12

why do larger alkanes release more energy per mole when they burn

Answer 12

more bonds to react

Question 13

why do alkanes make excellent fuels

Answer 13

they release lots of energy when they burn

Question 14

combustion of propane

C3H8(g) + 5O2(g) ->

Answer 14

3CO2(g) + 4H2O

Question 15

if you burn alkanes in limited oxygen

Answer 15

alkanes still burn

produce carbon monoxide CO and water

Question 16

combustion of methane in limited O2

2CH4(g) + 3O2(g) ->

Answer 16

2CO(g) + 4H2O(g)

Question 17

how is carbon monoxide poisonous

Answer 17

1. O2 in bloodstream carried by haemoglobin
2. CO better at binding to haemoglobin than O2. binds to haemoglobin before the O2 can
3. less O2 is carried round the body = oxygen deprivation.
   at high conc CO is fatal