Alkanes

Question 1

what is homolytic fission

Answer 1

the breaking of a covalent bond with the electron going to each atom forming 2 radicals

Question 2

what is heterolytic fission

Answer 2

the breaking of a covalent bond forming a cation (+ive) and anion (-ive).

Question 3

explain why alkanes do not react with common laboratory equipment

Answer 3

because they are fairly unreactive due to the presence of strong carbon to hydrogen and carbon to carbon single bonds which have no to little polarity.

Question 4

are alkanes polar or non polar

Answer 4

non polar as they have little difference in electronegativity between the carbon and hydrogen bond

Question 5

what type of bond do alkanes have

Answer 5

sigma bond

Question 5

what is a sigma bond

Answer 5

direct overlap of two orbitals from each bonding atom and positioned on a line directly between bonding atoms

Question 6

what are the shape of alkanes

Answer 6

tetrahedral 109.5 degrees
because of repulsion between these 4 electrons pair in the 4 sigma bonds result in a 3D arrangement around each carbon.

Question 7

Does branched molecules have a lower or higher boiling point compared to equivalent straight chain

Answer 7

Branched molecules has lower boiling point because have fewer surface area and hence less induced dipole-dipole interaction.The branches get in the way and prevent branched molecules from getting close together as straight chain molecules decreasing the intermolecular forces further

Question 8

What happens to boiling point as alkane chain increases why

Answer 8

B.p increases as there’s more surface area contact and so more number of induced dipole-dipole interactions.Therefore more energy to overcome reaction.

Question 9

Are alkanes rigid or can they rotate freely

Answer 9

Rotate freely as sigma bonds acts as an axes around which atoms can rotate freely

Question 10

What type of intermolecular force do alkanes have

Answer 10

Have London forces——> induced dipole-dipole interaction because the bonds are nonpolar

Question 11

How are halogenoalkanes formed from alkanes

Answer 11

Radical substitution

Question 12

In the presence of what does alkanes react with halogen

Answer 12

UV light and presence of sunlight

Question 13

What happens if oxygen was limited in combustion of alkanes

Answer 13

Hydrogen atoms in the alkanes oxidise to water but combustion of the carbon maybe be incomplete forming toxic gas CO or even C itself soot

Question 14

What are three stages of radical substitution

Answer 14

Initiation-breaking reaction to form free radical by homolytic fission
Propagation-chain part of the reaction where products are formed but free radical remains
Termination-free radicals removed stable product formed when two radicals collide and react they are removed from the mixture

Question 15

At room temperature and pressure the first 4 alkanes are gases but the first 4 alcohols are liquids explain why

Answer 15

Because alcohol have hydrogen bond (and van der wall forces )
Hydrogen bonds are stronger than van der wall forces in alkanes

Question 16

What’s the general formula for cycloalkanes

Answer 16

CnH2n

Question 17

Explain why substitution mechanism is likely to produce a mixture of organic products

Answer 17

Because substitution can replace any H atom

Question 18

What is aliphatic

Answer 18

Carbon atoms are joined joined by branched and unbranched chains or aromatic rings

Question 19

What is alicyclic

Answer 19

Carbon atoms are joined to each other in ring structures with or without branches

Question 20

What is aromatic

Answer 20

Some or all of the carbons are found in benzene rings