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Molar change in solution - Problem, tried solving dont understand

  1. Mar 4, 2014 #1
    1. The problem statement, all variables and given/known data

    How many degrees(Celsius) would the temperature rise if 4,0g of NaOH was initially dissolved in 50mL of water.

    2. Relevant equations

    Calculate the molar enthalpy change of solution based on this information:

    - 4g NaOH(s) gets dissolved in 250mL of water, and the temperature rose from 19,5 to 23.0 Celsius.
    - 4.18 J to raise temperature in 1 gram of water 1 Celsius.
    - Water density: 1,0g/mL.
    - No energy was exchanged with the surroundings before the temperature change was measured.

    I solved this and ended up with 36,575 kJ/mol

    3. The attempt at a solution

    Here is what I`ve tried:

    50ml of water = 50 grams
    Molar mass of water: 18,016 g/mol

    50/18,016= 2,7753 mol

    2,7753 mol * 36,575 kJ/mol= 101kJ

    101kJ * 1000= 101000 J

    101000/4,18 J/g * Celsius=24162

    24162/1000=24,16 Celsius ???

    19,5+24,16= 43 Celsius??

    I dont understand?
    The correct answer is from 19,5 to 37.0 Celsius.
     
    Last edited: Mar 4, 2014
  2. jcsd
  3. Mar 4, 2014 #2

    Borek

    User Avatar

    Staff: Mentor

    Moles of what?

    Do you mean 36.6 kJ or 36600 kJ?
     
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