[YOEVEN]

Hello, I did a lab today and I am having problems understanding it.

First I determined the heat capacity of a coffee cup calorimeter, no problem there.

-n :delta: H°=Ccal :delta: T+ms :delta: T

I have to now find the heat given off by the reaction of Mg with HCl.
I have the moles of Mg from the mass that was used=
.0988g/24.31g=.00406 moles
the Ccal was determined to be .5255
 :delta: T=4.82°C
what do I use for a mass?  Is it the .0988g of Mg? Or do I have to include the HCl?
Not sure here.  Also for "s", do I use 3.862J/g°C for Mg or do I use 4.184j/g°C because the Mg was reacted in a dilute solution.
Also could you give me a ball park number that I should be getting for  :delta: H for Mg formation?
Thank you.

[Borek]

what do I use for a mass?  Is it the .0988g of Mg? Or do I have to include the HCl?

Sum of both - but not just the masses, but their heat capacities (ms in your symbols). And as the solution was diluted, 4.184 is the correct number to use.