Question

what is the function of calorimetry in the experiment of determination of the enthalpy of formation of MgO?

Answer 1

A calorimeter is a device used for the science of measuring the heat of chemical reactions or physical changes as well as heat capacity.

So, you know that,
\[Q=mc \Delta T\]
Once you found Q (heat),
use the formula
\[\Delta H_f=\frac{Q}{n}\]
Where n is the number of moles.