1. The problem statement, all variables and given/known data Simple Coffee cup Calorimetry. Heat capacity of calorimeter was measured experimentally. Mg ribbons dissolved in aq HCl in coffee cup calorimeter and measurements taken. MgO was then dissolved in another setup of identical calorimeter and measurements taken. My question: Mg or MgO dissolves in HCl(aq) to form hydrated Mg ions but why can we ignore the enthalpy change of this hydration process? 2. Relevant equations - 3. The attempt at a solution Don't get it.