Difference between change of enthalpy of neutralization between copper and manganese carbonate

I was doing a calorimetry experiment to calculate the change in enthalpy during neutralization reactions between metal carbonates and hydrochloric acid. I experimented with 5 metal carbonates: magnesium, zinc, copper(II), manganese(II), and calcium.


I noticed that when I reacted $\ce{MnCO3}$ with $\ce{HCl}$ and $\ce{CuCO3}$ with $\ce{HCl}$, the temperature of the solution increased unusually higher than magnesium, zinc, and calcium carbonates. After calculating the enthalpy change per mole of $\ce{MnO}$ and $\ce{CuCO3}$ when reacted with $\ce{HCl}$, it was unusually higher. For the enthalpy change in neutralization for magnesium, I obtained a value of $\pu{-45.0 kJ/mol}$ while I obtained a value of $\pu{-377 kJ/mol}$ for copper(II) carbonate and $\pu{-240 kJ/mol}$ for manganese(II) carbonate. I have double-checked my stoichiometry calculations and no mistakes were found. Could anyone please explain the large difference in change of enthalpy for copper(II) and manganese(II) carbonate?


