[positiveion]

I'm doing a lab on the reaction between calcium carbonate and HCl.

My independant variable is the mass of calcium carbonate.

So basically, I add in different masses of CaCO3 to show that more CaCO3 = higher temperature therefore higher enthalpy change until CaCO3 becomes limiting reagant.

However, I still need to calculate the enthalpy change for stuff. And I'm supposed to do it like this:



(e.g. from a previous lab using different chemicals.) by plotting the temperature and extrapolating the initial temperature to use in enthalpy change calculations.

But for some reason something WEIRD happens with Calcium Carbonate and HCl. Though the higher masses of CaCO3 (near and post being in excess/being the limiting reagant) follow the normal situation of adding in CaCO3 and then temperature getting really high and then gradually dropping as the calorimeter fails to retain all the heat, the lower masses do not. For some reason, the smaller masses - once their tmperature shoots up it gradually CONTINUES going up!



That REALLY confuses me! I have a theory (entirely based on my own guesses) that the calcium carbonate really CLUMPS so unless its so majorly in excess that its everywhere then it takes a while for it to disperse despite my attempts to shake around and evenly disperse the reactants while conducting the experiment.  

Do you think that is an accurate guess/assumption? And if so, how should I write up my lab? Is there any way of doing it legitimately? Cause if I use these extrapolations to do my calculations all my final answers will be really messed up.. Should I just screw around with my data and like switch the temperatures? Ahh I don't know what to do :S.
Thanks so much for reading all that!