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Homework Help: How do you find the enthalphy change per mole of magnesium?

  1. Nov 19, 2011 #1
    1. The problem statement, all variables and given/known data
    In this calorimetry experiment, O.5 grams of magnesium is dissolved in 100.0 ml (100.0g) of diluted HCL (0.1mol/L) at an initial temperature of 29.50 C. The final temperature is 46.18 C.

    Q: Calculate the enthalpy change per mole of magnesium.


    2. Relevant equations

    I'm really confused about how will i get the the enthalpy change per mole for magnesium. Would it be the same as getting the enthalpy change per mole for magnesium chloride, because that's how i treated it and i don't think its the right answer. Can someone please help me?


    3. The attempt at a solution

    C) In this calorimetry experiment, O.5 grams of magnesium is dissolved in 100.0 ml (100.0g) of diluted HCL (0.1mol/L) at an initial temperature of 29.50 C. The final temperature is 46.18 C.

    The enthalpy change per mole of magnesium:

    mass of mg = 0.5 grams
    Molar mass of mg = 24.21g/mol
    moles of mg = (0.5grams)/(24.31g/mol)
    = .0206 moles of Mg

    H = q
    (Mg dissolving) = (calorimeter water)

    H = n Hsol and q=mc t

    mHCL = 100grams

    cwater = 4.18

    T = 46.18-29.50 = 16.18

    n Hsol = mc T

    Hsol(mg)= (mc T)/n
    = (100gramsX4.18 J/g C X16.68C)/(.0206)
    = 338990.3092 Joules
    = 338.99 KJ/mol
     
  2. jcsd
  3. Nov 19, 2011 #2

    Borek

    User Avatar

    Staff: Mentor

    I am not sure what you mean - you (correctly) calculated change per one mole of Mg consumed. That's it.
     
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