electrochem

Question 1

why cis isomer has higher BP?

Answer 1

1. dipole moments do not cancel out
2. overall dipole moment for mlc is produced
3. cis isomer is polar & permanent pd-pd exist btw mlc

Question 2

write eqn at anode/cathode

Answer 2

1. identify anode/cathode
2. identify what is undergoing ox/red (using Ecell values + qns context)
3. write ionic eqn (non-reversible arrow)

Question 3

write balanced eqn

Answer 3

1. write anode + cathode eqn
   * multiply until both have same no. of e-

Question 4

draw electrochem/electrolytic cell diagram

Answer 4

1. voltmeter
2. salt bridge
3. if standard electrode cell: draw H2/H+ cell
4. if gas present: 1 bar + 298K + electrode is platinum at bottom of gas chamber
5. sol. in 1moldm^-3

Question 5

calculations (find time/ current/ charge/ avogadro’s constant/ e- charge)

Answer 5

moles of e-

Question 6

calculation (find vol of gas produced)

Answer 6

mol= vol of gas (dm^3) / 24 (rtp) or 22.7 (stp)

Question 7

What happens to Ecell value when ppt occurs?

Answer 7

*testing POE

1. __ ppt formed
2. __ conc decreases
3. shifts POE of __ to left/right
4. E(_) js more/less positive
5. since Ecell=Ecathode - Eanode, Ecell becomes more/less +ve

Question 8

what happens to Ecell value when water is added?

Answer 8

• test POE

1. __ conc decreases
   :
   : (same as ppt)

Question 9

what happens to Ecell value when size of electrode decreases?

Answer 9

1. no change in E cell
2. size of electrode does not affect POE

Question 10

what happens to Ecell value when hexane is added to I2

Answer 10

1. I2 will preferentially dissolve in hexane
2. I2 is removed from aq phase
3. [I2(aq] decreases
4. shift POE…
   :
   : (same)

Question 11

calculate gibbs free energy

Answer 11

G= -nFEcell
n: no of moles of e-
G: calculated in Jmol^-1 > final ans in kJmol^-1

Question 12

Will reaction occur? (*link to spontaneity)

Answer 12

1. calculate Ecell
2. Ecell>0: reaction is spontaneous

OR

1. calculate G
2. G<0: reaction is spontaneous