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libelec
Nov9-09, 03:40 PM
1. The problem statement, all variables and given/known data

In discharge mode, calculate the variation in mass of the compounds of a lead-acid battery if the sufuric acid mass decreases by 294g (3 moles).

2. Relevant equations

The semirreactions:

Pb \to P{b^{2 + }} + 2{e^ - }
4{H^ + } + Pb{O_2} + 2{e^ - } \to P{b^{2 + }} + 2{H_2}O

3. The attempt at a solution

The only thing I could deduce was that if the H2SO4 decreases in 3 moles, then this means that 3 moles of PbSO4 were formed, along with 3 moles of H2O (since the relation is 1 mole of each of the former formed for each mole of H2SO4 consumed).

But I can't figure out what would happen to the Pb or the PbO2.

I have the answers: Pb increases in 1,5 moles and PbO2 decreases in 1,5 moles.

Any ideas?

Thanks

Borek
Nov10-09, 03:48 AM
Try with overall reaction equation.

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libelec
Nov10-09, 08:36 AM
But the overall reaction:

Pb + Pb{O_2} + 2{H_2}S{O_4} \to 2PbS{O_4} + 2{H_2}O

doesn't tell me why the Pb mass increases and the PbO2 mass decreases.

Borek
Nov10-09, 08:49 AM
Perhaps that means that the answer you were given is incorrect?

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libelec
Nov14-09, 03:12 PM
Yes, such was the case. Thank you.

Borek
Nov14-09, 06:30 PM
Yes, such was the case. Thank you.

Not that I am surprised :wink:

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