ibquestions Posted May 17, 2011 Report Share Posted May 17, 2011 Hey guys, So I have a lab I am currently working on (at the moment I am on the calculations) that has me stumped... My lab is about how the mass of CaCO3 affects the enthalpy change of this reaction: CaCO3 + 2HCl -> 2NaCl + CO2 + H2O. I have carried out all of my experiments using 5 separate values for the mass of calcium carbonate (i used a temperature probe during the experiment so i have graphs of the temperature change for each of them) but now i'm confused... usually i have to compare a theoretical result to an experimental result... but I don't know how I actually find the theoretical result in order to compare it to the value of the enthalpy change for my reactions. Does anyone have any ideas on how I am supposed to attain this value? Do I have to use hess' law and bond enthalpies? Any help is greatly appreciated Reply Link to post Share on other sites More sharing options...
Drake Glau Posted May 17, 2011 Report Share Posted May 17, 2011 The enthalpy change would be the difference in the enthalpies of formation. You would do the sum of the products minus the sum of the reactants using some standard enthalpy of formation values You'll learn this next year maybe, when you hit the HL addons Reply Link to post Share on other sites More sharing options...
ibquestions Posted May 17, 2011 Author Report Share Posted May 17, 2011 (edited) Haha ah we've been shown that reaction so, just to be clear, that is what I would use to get my theoretical results? And the actual enthalpies of formation for each element... are they written somewhere in some book or on the internet or something? One other quick question... would I then use 'q=mc(delta)T' and "(delta)H = (delta)H of the reaction/moles" to find my experimental results? Edited May 17, 2011 by ibquestions Reply Link to post Share on other sites More sharing options...
Drake Glau Posted May 17, 2011 Report Share Posted May 17, 2011 Experimental results would be using q=mc/_\T, that gives you the enthalpy change overall. But to compare to your theoretical you need it in H/mol so then you just divide by your moles for each mass value.Ummm you could probably find them online somewhere. There's a book called the CRC that has MASSIVE lists of theoretical values. It's a GIANT book, all lists of values for everything related to chemistry and/or physics. Reply Link to post Share on other sites More sharing options...
ibquestions Posted May 17, 2011 Author Report Share Posted May 17, 2011 oh i see, haha yeah I think my teacher has that in his office, i'll have to get the values from him thank you very much for your help Reply Link to post Share on other sites More sharing options...
ibquestions Posted May 17, 2011 Author Report Share Posted May 17, 2011 oh i see, haha yeah I think my teacher has that in his office, i'll have to get the values from him thank you very much for your help Reply Link to post Share on other sites More sharing options...
Drake Glau Posted May 17, 2011 Report Share Posted May 17, 2011 oh i see, haha yeah I think my teacher has that in his office, i'll have to get the values from him thank you very much for your help K, when using it please take note of what chart you're looking at. There's like 7 different enthalpy value tables. There's formation, combustion, lattice, atomization, vaporization (I think), bond enthalpies, probably many more honestly. Just make sure you're in the enthalpy of formation table. Also for your evaluation when you compare results. All those values are at stp, your lab environment was probably not. Reply Link to post Share on other sites More sharing options...
ibquestions Posted May 17, 2011 Author Report Share Posted May 17, 2011 (edited) oh shoot I just thought of one more question... I know this book has all the values, etc that allow me to find the theoretical... but am i using that same theoretical value to compare to each experimental value even though i have five because of the different masses? EDIT: so i should use the formation values, correct? and how do i account for the stp/rtp difference? Edited May 17, 2011 by ibquestions Reply Link to post Share on other sites More sharing options...
Drake Glau Posted May 17, 2011 Report Share Posted May 17, 2011 (edited) You won't be, you'll just discuss it in your evaluation. Since your mass is changing so is your moles and you are finding your H/mol. So as your mass changes the equation is changing with it. You should get similar results Bad example for the math 10/2=5 25/5=5 The moles went up, but so did the enthalpy, still divided into 5H/mol Edited May 17, 2011 by Drake Glau Reply Link to post Share on other sites More sharing options...
ibquestions Posted May 18, 2011 Author Report Share Posted May 18, 2011 but for the theoetical isn't there just one way to get the result? By finding the difference in the enthalpies of formation (the sum of the products minus the sum of the reactants using some standard enthalpy of formation values). How does this differ depending on mass?Sorry if you already answered that, I thought you were talking in relation to the experimental values :/ Reply Link to post Share on other sites More sharing options...
Drake Glau Posted May 18, 2011 Report Share Posted May 18, 2011 but for the theoetical isn't there just one way to get the result? By finding the difference in the enthalpies of formation (the sum of the products minus the sum of the reactants using some standard enthalpy of formation values). How does this differ depending on mass?Sorry if you already answered that, I thought you were talking in relation to the experimental values :/Your experimental enthalpy change will change, but your mass changes your amount of moles also so your experimental change in enthalpy won't be the exact same but should be close to the same number.It's like you get a H of 25 for 5g of something and then you do another trial using 2g and get a H of 10, both come out to 5H/molThe theoretical value from the tables and stuff should give you close to this number. Reply Link to post Share on other sites More sharing options...
ibquestions Posted May 18, 2011 Author Report Share Posted May 18, 2011 hahah i know this happened last time you tried to answer my question as well and i'm really sorry, but i truly don't understand what you're saying... are you saying the theoretical value will change or won't change? I know the experimental will, but i'm still confused about this theoretical. Reply Link to post Share on other sites More sharing options...
Drake Glau Posted May 18, 2011 Report Share Posted May 18, 2011 Theoretical won't change.Experimental will change but will be relatively the same each time (hopefully). Reply Link to post Share on other sites More sharing options...
ibquestions Posted May 18, 2011 Author Report Share Posted May 18, 2011 ah thank you I find that odd though... because it will just make the percentage error change for each experiment, but okay thank you for your help Reply Link to post Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.