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Homework Help: I need help with how to do change in enthalpy

  1. Nov 16, 2008 #1
    The problem says: Enthalpy is always reported with respect to a reactant. Calculate the enthalpy change, DeltaH, for each reaction in terms of kJ/mol for one of the reactants. (i.e either HCL or NaOH).

    I had three reactions:

    1. NaOH + HCL---->H20 +NaCl
    2.NH4Cl +NaOH---->H20 +NH3 +NaCl
    3. HCl +NH3---->NH4

    The first reaction I measured out 25.3mL of 2.0M HCl into a foam cup, then I dumped in 25.4mL of NaOH solution into the cup... my lowest temperature was 22.6 degrees C (before two solutions re combined., and my highest was 35.7 degrees C (when the solutions were mixed).

    The second reaction I measured 25mL of 2.0M NaOH into a foam cup and then dumped 25.4mL of 2.0M NH4Cl solution. My lowest temperature was 22.5 degrees C (before mixing), and highest was 23.8 degrees C (after mixing).

    The third reaction I measured 25.3mL of 2.0M HCl into a foam cup and then dumped 25.5 mL of 2.0M NH3 solution. My lowest temperature was 22.4 degrees C (before mixing), and highest was 31. 7 degrees C (after mixing thr two solutions.

    Can somebody help me and show me what to do possibly, I really have no clue. Thank you so much!
  2. jcsd
  3. Nov 17, 2008 #2


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    Science Advisor
    Homework Helper

    You need to figure out the heat of the reaction by the change in temperature of the water. What is the equation that needs to be used for this?

    Find the equation that relates enthalpy to energy.

    Then it is a matter of dividing by the appropriate units of the reactant to get your answer. If you have trouble , simply consult NIST or CRC.
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