theoretical heat of combustion different to experimental value- why? (1 Viewer)

[stacey**]

I'm doing a 2005 hsc Q on the heat of combustion and i need to give a reason why ther experimental valye for the heat of combustion of ethanol is different from the theoretical value........ i can only think of maybe wind chanaging the results..... and i dont even know if thats anywhere near right?!?!
if anyone could PLEASE HELP that would be excellent.
Also, does anyone know where we could get sample answers etc of rold Hsc's, the boardofstudies only has marking criteria and they dont help when u dont know the answer....
thanks heaps guys!!!!
earnestly awaiting your reply.........
stacey xoxoxoxox

 

[cagedflame]

Ok when you do your experiment to find the heat of combustion, heat can be lost in the process of heating up the ethanol. like the air, whatever you heated it in and so on. so your experimental value should be less than the theoretical value.

 

[pLuvia]

You can't get the theoretical value with the school experiment, but you should have noticed when doing it at school that the heat is lost by the surrounding environment, the metal equipment you used as it absorbs heat, measurement inaccuracies etc.

 

[Oberst Fan]

Also the school experiment doesn't undergo complete combustion...So your value will be lower than that in the SI Databook...

 

[theworldisround]

There should be a chemistry standards package available in your school library, or your science faculty. The standards package shows responses written by HSC candidates in chemistry to past HSC exams. These responses are grouped by their quality ie. band 5/6, band 3/4 and band 1/2.

 

[Forbidden.]

Heat is converted from one form to another...