Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Really need help! calorimetry

  1. Oct 22, 2008 #1
    to the admin. pls. don't delete this i figure it be easier to understand this if it's set up this way because its a prelab.thanks

    I. 89.7716 g of metal were heated to 99.8 °C and poured into a calorimeter containing 46.20 g of water at 28.45 °C.
    After stirring, the temperature of the water rose rapidly to 36.25 °C before slowly starting to fall.
    a) The Specific Heat of the metal _____________
    b) The Atomic Weight _____________
    Calculated using the rule of Dulong and Petit

    II. To a calorimeter containing 48.80 g of water at 28.85 °C, 7.0545 g of a salt was added with stirring. As the salt dissolved, the temperature rapidly changed to 31.45 °C before slowly returning to room temperature.
    c) The Heat of Solution ______________

    Given that the Heat of Formation of the solid salt is.... -180.59 Kj/mol
    and the Molecular Mass of the solid salt is.......... 143.69 g/mol
    d) The Heat of Formation of the Solution ______________ Kj/mol

    III. Given the reaction... AAA + BBB ---> CCC
    You add to a calorimeter 8.0 mL of 5.65 M AAA, 5.0 mL of water, and 12.0 mL of 5.51 M BBB. All of the above solutions were initially at 29.10 °C. After mixing, the temperature changed to 30.60 °C.
    Assume the density of all solutions is 1.000 g/mL and all solutions have the same specific heat as pure water.
    e) The Heat of Reaction in Kj/mol ______________

    i don't know how to get B D and E

    for A i got .264
    for B i divided .264 from 6 but the answer is wrong. i tried it with 6.2 but it i'm still not getting the right answer
    D. i really don't have a clue
    E. i'm given this formula but i'm stuck on limiting reagant
    (Volume in mL)(Molarity) = millimoles
    VolumeHCl + VolumeNaOH+ Volumewater = Volumeliquids
    Temperaturefinal-Temperatureinitial = Temp. Changeliquids
    (Massliquids)(-Temp. Changeliquids)(4.18 j/gºC) = Energy Change
    Energy Change/[(1000 j/Kj)(Moles of Limiting Reagent)] = DH Reaction

  2. jcsd
  3. Oct 24, 2008 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Can you show how you got that? And please include units. I think you did a unit conversion incorrectly, but without seeing your work and what units you mean to use, there is no way to tell.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook