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Topic: Really need help on Enthalpy, 75% of lab grade.  (Read 2316 times)

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Offline narcoleptic_insomniac

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Really need help on Enthalpy, 75% of lab grade.
« on: November 30, 2009, 02:43:59 PM »
Chemistry forum, i really need you on this one!!!!
 
This counts for 75% of my lab class, i need to do this right =/. If you can just show me how to some parts of each table, that'd be great.

I need to fill in the following table using the data im showing you. Basically the boxes that aren't filled, i need to solve for.

Info for Ammonium Nitrate: *50mL water was used


The tables i need to fill out:

Offline renge ishyo

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Re: Really need help on Enthalpy, 75% of lab grade.
« Reply #1 on: November 30, 2009, 04:32:56 PM »
I think you can use this formula to find the enthalpy:

Q = cm :delta: T

If you ignore pressure volume work then Q can be approximated as the enthalpy change. For c, use the heat capacity for water of 4.184 J/g*0C, for m use the mass of *water* in grams (approximate 50mL of water as 50g of water and it should be OK), and for  :delta: T the difference in temperature in 0C.

Once you have the enthalpy you can write that number as the energy released per 2 grams of your substance (or 4 grams for the second example). For instance say that you found that Q = 100 J in your earlier calculation for your first example. The energy per gram would be: 100J/2g = 50 J/g. Use the molecular weight to convert J/g to J/mol and finally convert J to kJ to report your final answer.

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