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Topic: Electrolytic Cell Do now: p.19 in packet, cross out # 19 and do # 20 and #21. must label anode/cathode . Chemical rxns can produce electricity = galvanic (voltaic) cell OR Electrical energy used to carry out chemical reactions= electrolytic cell . - PowerPoint PPT Presentation
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Topic: Electrolytic Cell
Do now: p.19 in packet, cross out # 19 and do # 20 and #21. must
label anode/cathode
• Chemical rxns can produce electricity = galvanic (voltaic) cell
OR• Electrical energy used to carry out chemical
reactions = electrolytic cell
Electrolytic Cell need electrical energy so NONSPONTANEOUS
Chemical Potential
Energy
ElectricalPotentialEnergy
Galvanic Cell
Electrolytic Cell
Galvanic cell is a battery
Electrolytic cell needs a battery
Electrolytic Cells• Nonspontaneous• Need battery or power supply• Consumes energy = endothermic
What’s the difference?
anode catode
Battery in one.Electrons in galvanic flowing from – to +Electrons in electrylic flowing from + to -
Electrolytic Cella Fat Red Cat ate an Ox
Use Table J, but oppositeMore active metal = cathode = negative
Less active metal = anode = positive
Galvanic CellA Fat Red Cat ate an Ox
Use Table J More active metal = anode = negativeLess active metal = cathode = positive
e- e- e-
NONSPONTANEOUS e- flow Anode to Cathode
But from + to –(opposite then we’d think)
That’s why we use the battery
SPONTANEOUS e- flow Anode to Cathode
from – to + (just like we’d think)
That’s why it’s spontaneous
e- e- e-
A POX on Electrolytic Cells
• Anode – Positive – Oxidation
A pox = a diseaseAnd electrolytic
cell behave differently like
they are diseased?!
Various types of electrolytic cells1. Fused Salt Cells – used to purify metals (Fused means melted = molten salt cell)
• Add NaCl (s) and melt it• Now NaCl (l)
• Why melt it?!
• Why add CaCl2(s)??!
• Na+1 is reduce to Na(l)
• Na(l) is less dense then NaCl(l) so it floats on top
• 20,000 tons of Na are produce this way in the US every year
Molten b/c need ions
Lowers MP – don’t need as much heat
Fused Salt Cell (Molten salt cell)
(l)
+
Na+
Cl-
Na+
Cl-
-
Na+ + 1e- NaCl- + Cl + 1 e-
Gain electronSo reduced So cathodelose electron
So oxidizedSo anode
BUT WAIT SOMETHING IS WRONG WITH OUR ANODE
22 2
e- e- e- e-
Various types of electrolytic cells2. Electroplating A layer of a second metal is deposited on the metal electrode that acts as the cathode• Used to enhance the appearance of metal
objects and protect them from corrosion.
Various types of electrolytic cells2. Electroplating • cathode = object to be
plated• anode - made of metal
want to plate on object• solution: contains ions of
plating metal
NO3-
NO3-
+-
Ag+ + 1e- Ag
Gain electronSo reduced So cathode
Ag Ag+ + 1e-
lose electronSo oxidizedSo anode
e- e- e- e-
3. Electrolysis of H2O
H2 is produced at one electrode, O2 at the other.
2H2O + energy 2H2 + O2
Can you tell from the picture which electrode is producing H2?
What do every one of these have in common?