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Homework Help: Question regarding energy from chemicals (M.C.Q)

  1. Oct 19, 2011 #1
    Q. A volume of 100 cm3 of 1 mol dm3 sodium hydroxide solution was added to 100 cm3 of 1 mol dm3 hydrochloric acid.The maximum rise in temperature recorded was T1.The experiment was repeated with 50cm3 of each solution and the rise in temperature this time was T2. It is found That

    A) T1 Is Equal To T2
    B) T1 Is Half The value Of T2
    C) T2 is half the value of T1
    D) T2 Is a quarter the value of T1.

    I think the Ans Should Be C as the volume is decreased...
    What do you think as the answer given is A...

    reply quickly... :-)
  2. jcsd
  3. Oct 19, 2011 #2


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    Science Advisor

    The volume is decreased, but the total energy of reaction is decreased in proportion. Remember energies of reaction are per mole, so if you cut the number of moles of reactant in half, the total energy liberated is also cut in half.
  4. Oct 19, 2011 #3
    can you explain it in further detail...
    examples would be appreciated..
  5. Oct 19, 2011 #4


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    Staff: Mentor

    Assume 1 mole of NaOH reacting with 1 mole HCl liberates energy Q. Calculate how much energy is liberated in both cases (in terms of Q). Calculate masses of solution in both cases. Calculate ratio of energy liberated to final mass of the solution for each case (again in terms of Q, assume density of 1g/mL). What did you get?
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