chapter 12

Question 1

what is the general formula for alkanes?

Answer 1

CnH2n+2

Question 2

what are the uses of alkanes?

Answer 2

fuels e.g petrol, diesel

Question 3

are alkanes saturated or unsaturated and what does this mean?

Answer 3

saturated, only have single covelant bonds

Question 4

what kind of bonds do alkanes have?

Answer 4

sigma bonds

Question 5

what can a sigma bond be?

Answer 5

a c-c bond or a c-h bond

Question 6

how does a sigma bond form?

Answer 6

it forms as a result of the overlap of two orbitals, 1 from each bonding atom

Question 7

where is a sigma bond positioned?

Answer 7

directly between the bonding atoms

Question 8

what is the shape of alkanes and why?

Answer 8

tetrahedral, it has 4 bonding regions and 0 lone pairs,

Question 9

what is the bond angle of alkanes?

Answer 9

109.5 degrees, all 4 bonding regions repel each other equally

Question 10

what do sigma bonds allow the molecule to do?

Answer 10

it acts at an axes at which atoms can move freely around eachother

Question 11

what is the process used to seperate crude oil?

Answer 11

fractional distillation

Question 12

what does the boiling point depend on?

Answer 12

london forces

Question 13

what are london forces?

Answer 13

forces that exist between molecules in close surface contact

Question 14

what happens to the boiling point when the chain length increases

Answer 14

the boiling point increases

Question 15

why does boiling point increase as chain length increases

Answer 15

as chain length increases molecules have high surface area, thus more surface contact between molecules, thus there are greater london forces, so more energy is required to overcome the forces

Question 16

what effect does branching have on boiling point?

Answer 16

it has a lower boiling point

Question 17

why does boiling point decrease as alkanes have branches?

Answer 17

there are fewer surface point of contact between molecules of the branched alkanes, thus there are fewer london forces.
branches gets in the way of branched molecules getting closer together, so there are weaker intermolecular forces, thus less energy to break them, thus lower boiling point