Alkanes and Halogenoalkanes

Question 1

what is the general formula for alkanes?

Answer 1

Cn H2n+2

Question 2

are alkanes saturated or unsaturated hydrocarbons?

what does that mean?

Answer 2

saturated hydrocarbons

only contain single bonds

Question 3

what is cracking?

Answer 3

breaking long-chain alkanes into smaller hydrocarbons

Question 4

describe a cycloalkane

Answer 4

have different general formula to alkanes
CnH2n
are still saturated

Question 5

describe two different types of cracking

Answer 5

thermal cracking
high temp
high pressure 70atm
produces alkenes (good for polymers)

catalytic cracking
high temp
low pressure
zeolite catalyst
motor fuels

Question 6

describe fractional distillation

Answer 6

crude oil is vaporised
as you go up column it gets cooler
each fraction condenses at different temp

Question 7

which two compounds are produced when an alkane burns completely?

Answer 7

carbon dioxide and water

Question 8

under what conditions does incomplete combustion of a fuel take place?

Answer 8

when there is not enough oxygen

Question 9

name four pollutants that can be produced when a fuel is burnt and their environmental problems

Answer 9

carbon monoxide gas - poisonous
carbon - soot causes breathing problems
sulfur dioxide - acid rain
unburnt hydrocarbons and nitrogen oxides - smog(ground level o zone) respiratory problems

Question 10

how does burning fossil fuels cause acid rain?

Answer 10

fossil fuels containing sulfur when reacted form sulfur dioxide

sulfur dioxide when in the atmosphere dissolves in the moisture forming sulfuric acid

Question 11

what is a free radical?

Answer 11

a particle with an unpaired electron

Question 12

what is the equation for the reaction with methane and chlorine in the presence of UV light?

Answer 12

Cl2 > 2Cl*
Cl* + CH4 > CH3* + HCl
CH3* + Cl2 > CH3Cl + Cl
Cl* + CH3* > CH3Cl

Question 13

why is having an ozone in the upper atmosphere beneficial to humans?

Answer 13

it acts as a chemical sunscreen
absorbs ultraviolet radiation from the sun stopping it from reaching us
ultraviolet radiation can cause sunburn or even skin cancer

Question 14

name two past uses for CFC’s

Answer 14

coolant gas in fridges

propellants in aerosols

Question 15

why is there an alternative to CFC’s and what is it ?

Answer 15

CFC’s were causing damage o the ozone
alternatives contain no chlorine
HCF’s (hydrofluorocarbons) and hydrocarbons

Question 16

why are carbon halogen bonds polar?

Answer 16

halogens are far more electronegative than carbon so the bonds are polar

Question 17

what is a nucleophile?

Answer 17

electron pair donor

Question 18

what compounds are formed from the reaction with a halogenoalkane and aqueous potassium hydroxide?

Answer 18

alcohols

Question 19

what compounds are formed from the reaction with a halogenoalkane and potassium cyanide?

Answer 19

nitriles

Question 20

what compounds are formed from the reaction with a halogenoalkane and ethanoic ammonia?

Answer 20

amines

Question 21

why does iodoethane react faster than chloroethane with nucleophiles?

Answer 21

the bond strength (enthalpy) decides reactivity

lower bond enthalpy’s are substituted quicker