Chemistry
posted by Ashley on .
So I am writing a lab report and Im stuck with calculating the enthalpy change of combustion of the following reaction:
Mg+2HCl> MgCl2+H2 .I am given the mass of Mg which is 5g and the concentration of HCl which is 2M and the volume of HCl which is 50 cm^3.I found the limiting reactant which was HCl and i have to measure the ÄÇ of combustion..I know that HE(HEAT ENERGY)=m x c x ÄT and the change in temperature is 10 degrees celsius. I also know that in order to find ÄH we divide HE with n which is the number of moles of the limiting reactant..can anyone please help me find the ÄH?i DON'T know whose mass to use, i know i have to use the heat capacity of water..and i don't know whether i have to convert temperature into Kelvin measurement.

Frankly, I don't know how you are to calculate heat of combustion when you didn't combust Mg but reacted it with HCl instead.
You measured the T difference of the water; therefore, find the q from mc*delta T by using the mass of water (50 cc = 50g if the density is 1.00 g/cc) and the specific heat of water. 
we were asked to find the enthalpy change because it is an exothermic reaction. Don't i have to convert cm^3 into dm^3 in the equation?when i divide the Heat energy with the number of moles in order to get enthalpy change do i put the moles of the limiting reagent?

You want the mass of the water and the volume of the water is 50 cc. Since the density is 1.00 g/cc, the mass is 50 g. You CAN convert cc to dm^3 if you want to use a different value for density in g/dm^3. After finding q, then delta H rxn = q/n for the limiting reagent which gives J/mol for the unit.