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Variation of masses in lead-acid battery due to H2SO4 mass variation

  1. Nov 9, 2009 #1
    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:

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

    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
     
  2. jcsd
  3. Nov 10, 2009 #2

    Borek

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    Staff: Mentor

    Try with overall reaction equation.

    --
    methods
     
  4. Nov 10, 2009 #3
    But the overall reaction:

    [tex]Pb + Pb{O_2} + 2{H_2}S{O_4} \to 2PbS{O_4} + 2{H_2}O[/tex]

    doesn't tell me why the Pb mass increases and the PbO2 mass decreases.
     
  5. Nov 10, 2009 #4

    Borek

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    Staff: Mentor

    Perhaps that means that the answer you were given is incorrect?

    --
    methods
     
  6. Nov 14, 2009 #5
    Yes, such was the case. Thank you.
     
  7. Nov 14, 2009 #6

    Borek

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    Staff: Mentor

    Not that I am surprised :wink:

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