[Eniyx]

In the reaction
A + B -> C + D  (exothermic reaction)
m =170.2g
c  = 4.18
Delta T = 2
n= 0.0419

so m c deltaT = n DeltaH
Delta H = -33kj


The question is what would happen to the H = -33kj if some of the mass lost or not reacted. I tried to do it using real numbers and i got H = -44kj.
I don't understand why H increased when i reduced the mass, i thought it would decrease.
Thanks in advance.

[Grundalizer]

Where are your calculations?  What numbers did you use?  If you put a lower "m" into that equation and keep the other numbers you have,  :delta:H does decrease, not increase.  Putting units on your numbers also helps people to better answer your question.  As I see it, changing the "m" would also change the n(mols of substance),  :delta:T, and  :delta:H in your equation, so the  :delta:H is directly proportional to the mass that undergoes the reaction. 

If you burn a twig  you get X amount of energy, if you burn a giant log you get Y amount of energy, obviously Y > X because there is more "stuff" to burn in a log.  But you could also chop that log (Y) up into a bunch of little pieces almost like a whole bunch of twigs (X's) and burning the 100 X's would still give you the same amount of energy as burning the one Y. 

I think the X and Y analogy is really confusing, but think of it logically.  If you are doing an exothermic reaction, the more mass of reactants you start with, the more energy is produced, likewise, if you start with less mass, you will produce less heat.

I think you did something wrong with a number in a calculator.  Also, think of it as variables, as changing "m" will change some of your other variables in the equation making it almost impossible to make up "real numbers"

[Eniyx]

Ahh, the problem was because i didn't change temperature and the m c delta T is directly proportional to n delta T was very helpful, i didn't realize that until you pointed it out. Many thanks