91.7g of HCl solution was added to the calorimeter and brought to a constant temperature. Then 0.5278g of MgO was added and the temp rose from 25.65C to 32.60C and held steady. Then 0.0185g of Mg was added and the temp again rose from 30.35C to 32.20C

Calculate
the Cp for the Calorimeter?
Delta H = -127 Kj/mol

You have two reactions going on. Delta H = -127 kJ/mol for which of the two reactions. Next, what is the delta H for the other reaction.

One reaction is
MgO + 2HCl ==> MgCl2 + H2O.
The other reaction is
Mg + 2HCl ==> MgCl2 + H2O.