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March 24, 2017

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A 65.0 g sample of 0.600 M HI at 18.46 degrees celsius is added to 84.0 g of solution containing excess KOH, also at 18.46 degrees celsius. The final temperature is 21.96 degrees celsius. Calculate the enthalpy of H for the reaction.

Assume the specific heat of the solution is 4.184 J/g(degrees celsius), and the calorimeter has negligible heat capacity .

HI(aq) + KOH(aq) --> KI(aq) + H2O(l)

enthalpy of H ?

  • Chemistry-Thermochemistry (grade 12) - ,

    You have 65.0 g soln from HI and 84.0 g H2O with the KOH so total mass soln is 149 g.
    q = mass H2O x specific heat water x (delta T).

    USUALLY delta H for a reaction is done in kJ/mol. This problem has no easy way to get to moles but q/mol = J/mol and you can convert that to kJ/mol if needed. If you assume the density of the HI solution is 1.00 g/mL, that can be used to solve for mols HI; e.g., 65 mL of 0.600 M HI would be moles = M x L = 0.600 x 0.065 = ? and you can use that for mols. I doubt that the density is 1. g/mL.

  • Chemistry-Thermochemistry (grade 12) - ,

    Awesome

    I am defiantly starting to understand this stuff better.

    .065L x (.600 mol/L) = 0.0390 mol

    q=MC(delta T)
    = 149g x 4.184 J/g(C) x 3.5 celsius
    = 2181.9 J
    =2.2 kJ

    Then I did
    2.2 kJ / 0.0390 mol
    = 56 kJ/mol

    for my final answer I got 56 kJ/mol

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