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Homework Help: Need serious help with these enthalpy of neutralisation calculations

  1. Mar 1, 2007 #1
    ok i keep reading that ideally they (neutralisation enthalpies) are meant to be around 58KJ

    here is my problem:

    im reacting 50cm3 of NaOH with 25cm3 of HCl

    the HCl is 1 mole NaOH is also 1 mole.

    my moles calculation is: (1x25)/1000 which gives me 0.025

    the i do :

    ((mass x specific heat x change in temp)/moles)/1000

    i get -25.4 which is no where near 58 ish...

    same thing when i use nitric acid instead, i end up with 27.08. However when i use sulphuric acid i get a result of 52.416 (sulphuric acid is 0.5 molar)

    so my question is, am i getting something wrong? im using the mass of the substance needed to neutralise the acid for mass (reading it off a graph) & im using 4.2 for specific heat

    also is there any reason for why some are better at neutralising is it like to do with more H+ ions ?

    i would really appreciate any help
     
  2. jcsd
  3. Mar 1, 2007 #2

    GCT

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    Homework Helper

    Neutralization enthalpies are based on the net ionic equation for water

    H+ (aq) + OH- (aq) ----> H2O (l)

    that's why the enthalpies are fairly the same. The slight differences may pertain to the hydration interactions of the respective components (for instance, Na + and Cl-) with water.
     
  4. Mar 3, 2007 #3
    thanks, =)
     
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