4. Using the total electrochemical reaction for a lead-acid battery and the tabl

Question

4. Using the total electrochemical reaction for a lead-acid battery and the table of standard reduction potentials Pb(s) + PbO2 (s) +4H+ (ag) + 2 SOA (ag) 2 PbSO4 (s) + 2 H2O (l) Write the reaction taking place on the anode (oxidation) and the reaction for the cathode (reduction) Is this reaction spontaneous or non-spontaneous? How do you know? a. b. c. Why might sulfuric acid (H2504) work better as an electrolyte in batteries than acetic (C2H402) or hydrochloric (HCl) acids? d. Why is it important to recycle your batteries, and car batteries in particular?

Explanation / Answer

4.a) Anode is a lead plate and the cathode is paste of spongy lead dioxide pressed into a lead grid

Lead plates fit in-between the lead dioxide plates

Various plates are separated from the adjacent ones by insulators like strips of wood/rubber/glass fibre

Entire combination is immersed in approx. 20-21 % dil. H2SO4

(density 1.2-1.3) acting as electrolyte

Oxidation: Pb (s) Pb2+ + 2 e- , Pb2+ + SO42- PbSO4

Pb (s) + H2SO4(aq) PbSO4(s) + 2H+(aq) + 2 e-

Reduction: PbO2(s) + 2H+(aq) + H2SO4(aq) + 2 e- PbSO4(s) + 2 H2O(l)

Overall net discharging equation : Pb(s) + PbO2(s) + 2H2SO4(aq) 2 PbSO4(s) + 2 H2O(l) + Energy

E°cell = E°PbO2/PbSO4 - E°PbSO4/Pb = 1.74 V – (-0.28 V) = 2.02 V

4.b) In lead -acid battery during discharge equations , these are called Voltaic cells or galvanic cells, these are sontaneous reactions because of DeltaH is possitive.

In lead -acid battery during chargeing equations , these are called Electrolytic cells, these are Non-sontaneous reactions because of DeltaH is negative.

4.C)

1. Dil H2So4 is a very polar liqiud,with dielectric constant 100 . This property arises from that it can dissociate by protonating itself(Auti- prottolysis)

2.Dil H2So4 is an excellent solvent for many reactions

3.the reaction of Dil H2So4 with water produces large amount of heat, and its therefore called an exo thermic reactions

4.D)

Yes. it is important to recycle batteries because

battery materials pose no threat to human health when in use ,but batteries discord improperly can have dangeorous health and environmental consequences because of heavy metals.

In the world, most of the countries are prohibit people from throwing lead-acid battery into the trash.

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