A calorimeter contains 21.0 mL of water at 11.0, ^{circ}C. When 2.50 g of rm X (a substance with a molar mass of 65.0 g/mol) is added, it dissolves via the reaction
rm X{(s)}+H_2O{(l)} rightarrow X{(aq)} and the temperature of the solution increases to 28.5, ^{circ}C.
Calculate the enthalpy change, Delta H, for this reaction per mole of rm X.
Assume that the specific heat and density of the resulting solution are equal to those of water [4.18 rm J/(g cdot {^circ C}) and 1.00 rm g/mL] and that no heat is lost to the calorimeter itself, nor to the surroundings.