I know the calculation will be higher, but I need help explaining.

Question

A student is determining the enthalpy of solution for ammonium nitrate by adding ammonium nitrate to a calorimeter and measuring the temperature change. 

The accepted value is ΔHsol’n = 25.7 kJ/mol. 

A student, not paying attention, adds 1.5g of ammonium nitrate instead of 1.0g. When they perform their calculations, they use 1.0g as the mass.  

Will their calculation result in an answer that is higher than the accepted value or lower? Explain.

Answer 1

They actually added more moles than they were supposed to (1.5 g is more moles than 1.0 g), so the heat generated will be greater than theoretical, and the temperature will rise more than had they added the correct amount. Finally, they will divide by their answer by a fewer number of moles (corresponding to 1.0 g instead of the actual 1.5 g), which will further make their answer greater than expected.