calculate delta H for the reaction

Question

When 1.045 g of CaO is added to 50 mL of water at 25 degrees Celsius in a caloriemeter, the temp of the water increases to 32.3 degrees Celsius. Assuming the specific heat of the solution is 4.18 J/K*C and that the calorimeter itself absorbs a negligible amount of heat, calculate delta H (enthalpy in kilojoules) for the reaction

CaO(s) + H20(l) ---> Ca(OH)2(aq)

Answer 1

Since the molar mass of CaO is 56g,   1.045 g  is equivalent to 0.0187 moles.

Since the temperature of the solution increases by 7.3 degrees, the equation for the molar enthalpy is

 

ΔH 0.0187 =  7.3  4.18  51.045.    which implies that the molar enthalpy =   83293 J/mole or 83.29 kJ/mole

 

The factor of 51.045  is there because the mass of 50mL water is 50g to which 1.045 g of CaO is added.