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Calculating Heats of Formation with 2 Datas.

  • 09-05-2015 4:00pm
    #1
    Registered Users, Registered Users 2 Posts: 204 ✭✭


    So I have no trouble calculating it with 3 datas given as per the picture of the revise wise method. But how would one go about calculating it(using that method) if you were only given 2 formulas equations.


Comments

  • Registered Users, Registered Users 2 Posts: 10 Trekker47


    It seems like it's the same as when there's 3 data given, here's my (hastily done) worked solution; hopefully it makes sense :P
    http ://i(dot)imgur(dot)com/uTphXnf(dot)png (Apparently I can't post images since I'm new, so you're gonna have to piece together the url, sorry)


  • Registered Users, Registered Users 2 Posts: 204 ✭✭iCrazzy


    Any chance you can do it using that method from the revise wise.
    I dont really understand how you do it. And what is up with the lines across.
    Thanks


  • Registered Users, Registered Users 2 Posts: 10 Trekker47


    I did out an explanation of my method which might help; it's dead easy, the only slightly tricky bit is working out the equations if they're not given to you, like they might say "Given that the heat of combustion of carbon is -393KJ", in which case you can work out that C + O2 -> CO2.
    http ://i.imgur.com/OQ8tArA.png?1
    I've never seen your method before so I'd need to have a couple of worked examples using the equations to learn it from, sorry about that.


  • Registered Users, Registered Users 2 Posts: 204 ✭✭iCrazzy


    Trekker47 wrote: »
    I did out an explanation of my method which might help; it's dead easy, the only slightly tricky bit is working out the equations if they're not given to you, like they might say "Given that the heat of combustion of carbon is -393KJ", in which case you can work out that C + O2 -> CO2.
    http ://i.imgur.com/OQ8tArA.png?1
    I've never seen your method before so I'd need to have a couple of worked examples using the equations to learn it from, sorry about that.

    Thank you, I get everything apart on how you calculated the 3rd equation

    The only part I can figure out is that
    Ca+C+O2
    CaCO3

    There is 3 oxygens on the left, so should there not be 3 oxygen in the right or make this to balance:
    2Ca+2C+3O2
    2CACO3

    Why do you have the half


  • Registered Users, Registered Users 2 Posts: 10 Trekker47


    Well we can only find oxygen as O2, it doesn't come as just O, 3O2 would really be 6O.
    Hence 1.5 O2 is actually 3O. Hope that helps :)


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  • Registered Users, Registered Users 2 Posts: 4,080 ✭✭✭EoghanIRL


    I've never seen the method in the revise wise. I wouldn't use it myself. With the other method you can check your work to see if you are right much more easily.


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