Alkanes

Question 1

What are alkanes?

Answer 1

alkanes have a general formula of CnH2n+2, are unreactive towards most chemical reagents because there is a small electronegativity difference between carbon and hydrogen.

Question 2

What does combustion undergo with alkanes?

Answer 2

alkanes undergo combustion in excess oxygen or air to form carbon dioxide or water, incomplete combustion forms carbon monoxide

Question 3

What is cracking of alkanes?

Answer 3

is the thermal decomposition of alkanes into short chain alkanes and alkenes. it can be done during 400-500 C and with a catalyst of SiO2 and Al2O3

thermal decomposition without a catalyst can be done during 700-900 C

Question 4

What is cracking a source of?

Answer 4

Hydrogen

Question 5

What happens with halogenation?

Answer 5

when methane and chlorine are mixed in the dark there is no reaction, but when mixed with ultraviolet a variety of products is formed, this is a substitute reaction

Question 6

What is a substitute reaction?

Answer 6

is a reaction where one atom or a group of atoms is replaced by another

Question 7

What are reaction mechanisms?

Answer 7

shows the step in bond breaking and making with reactants converting into intermediates then products

Question 8

What are 2 ways in which a bond can break?

Answer 8

by homolytic & heterolytic fission

Question 9

What is homolytic fission? and how is it represented?

Answer 9

two shared electrons are split equally, the movement of the single electron is shown by a fishhook arrow

Question 10

What is heterolytic fission?

Answer 10

two shared electrons are split unequally, one atom gets the 2 electron and become negatively charged, the next atoms becomes electron deficient so it becomes positively charged, the movement of the pair of electrons is shown by a curve arrow

Question 11

What are free radicals?

Answer 11

are atoms or a group of atoms with unpaired electrons, the unpaired electrons are represented by a dot

Question 12

What are alkenes?

Answer 12

alkenes have a general formula of CnH2n, alkenes are non polar but they are more reactive than alkanes because of the double carbon bond with an electron rich area which can be attacked by positively charged reagents

Question 13

What is an electrophile?

Answer 13

is a positively charged reagent which attacks an electron rich area of a molecule

Question 14

What is an example of an electrophile?

Answer 14

H+ ions

Question 15

What is an addition reaction?

Answer 15

is where a single products is formed from 2 reactant molecules and no other product is made

Question 16

What’s the bromine test for alkenes?

Answer 16

use aqueous bromine(bromine water) to test for the carbon double bond in alkenes, it can also be used to test for unsaturated compounds

when the bromine water is addd to the unsaturated compound the colour changes from orange/red brown (original bromine water) to colourless