Brightstorm Q & A : How do I calculate the experimental value for change in enthalpy for Mg(s)+2HCl(aq)-->MgCl2+H2(g)? The question also tells me to include the mass of Mg with the mass of HCl solution in the calculation of q. (this is form an experiment). The mass of Mg is .481 grams and the volume of HCl is 99.9 mL or 99.9 grams. The initial temp is 19.2 centigrade and the final is 40.0 cenitgrade. I found the Enthalpy to be -307.2 kJ but im not sure if it is right