unit 3 aos 2 Flashcards
what is a spontaneous reaction?
a reaction which occurs by itself
what needs to be inputted to force a non-spontaneous reaction?
electrical energy
electrolysis
the input of electrical energy is to force a non - spontaneous reaction
- electrons are forcefully moved in the opposite drection
what are cells in electrolysis called?
electrolytic cells
GALVANIC vs ELECTROLYTIC : type or redox reaction
G: spontaneous redox reaction
(strong oxident/reductant pair)
E: non - spontaneous redox reaction
(weak oxident/reductant pair)
GALVANIC vs ELECTROLYTIC: energy conversions
G: chemical TO (produce) electrical
E: (consumes) electrical TO chemical
ELECTROLYTIC set up
- one shared electrolyte ( bc not a spontaneous reaction = reactants will not react with eachother if placed togeather)
- no salt bridge
- both electrodes in the shared electrolyte
- cathode is ALWAYS inert
how do you know which side is positive and negative in a cell?
TALLER line = positive
SHORTER line = negative
what reaction occurs at each electrode?
SAME as galvaniic:
- anode: oxidation
- cathode: reduction
POLARITY just CHANGE
ion movement
cathions TO cathode
anions TO anode
why is a salt bridge not required?
bc the movement of electrolytes maintain electric neutrality
what to do to ensure that the electrolytic reaction IS ACCURATLY predicted
write out all speices present
SO CONSIDER WATER
what observations could be made in electrolytic cells?
- change in mass ()
- change in pH
- bubles forming
- colour changes (more/less intensly..)
as a last resort = volume
cathode reactivity in electrolysis
- strongest reductant MUST BE PRESENT and the ANODE
- metals at the cathode are considered UNREACTIVE thus are inert
what is the formula to calculate the EMF of a cell
EMF = oxident = reductant
what voltage is reqired for electrolysis
A voltage that is GREATER THAN the difference in EMF calculated
what conditions are electrochemical series constructed at?
SLC and 1.0M
when would cloride ions react more preferentially than water?
ON ECS cl is just above water SO
at concentrations greater than around 4.0M.
- at such concentrations, the cloride ions would become a stronger reductant and react in preference to water
what about sodium ions?
on ECS Na is a few species below water SO
even at high concentrations, sodium ions would not react in preference to water
MOLTEN definition
the liquid form of solid extremly hazardous substance at HIGH temperatures, which is normally in solid form at SLC conditions
is water present in molten conditions?
NO, so do not consider water when finding the strongest oxident/reductant pair
how do the states change in molten conditions?
(aq) becomes
purpose of electrolysis
Produces products unlikely to exist in nature.
purpose of molten cells???
molten electrolyte purpose
to react with species weaker than water
what material is typically used at anode?
graphite because it is inert and cheap
platinum is also inert BUT more expensive than graphite
what material is typically used at cathode?
iron, because the cathode is unreactive in these cells and even cheaper than graphite
