Enthalpy change - ocr chemistry - help !!

ii. Student 2 carries out the same experiment but uses twice the mass of CaCl2. All other
quantities are very similar to Student 1's experiment.
Predict any differences between the temperature change and the calculated value of
ΔsolH from the experiments of the two students. Explain your reasoning.

- I don't understand why the enthalpy change of solution does not change. Is it always the same no matter what you do to the reaction conditions? Could someone please explain - thank you

Enthalpy = (energy change)/(moles of substance used)

If you are using twice as much of the substance, you are releasing twice as much energy. You are also using twice as many moles of substance.

Suppose student 1 used 1 mole of CaCl2 and that released Q kJ of energy.

The enthalpy change = (Q kJ)/(1 mol) = Q kJ/mol

Now suppose student 2 used 2 moles of CaCl2 and so 2Q kJ of energy must have been released:

The enthalpy change = (2Q kJ)/(2 mol) = Q kJ/mol