There are couple of ways to determine the ΔH of a reaction. Q = MCΔT would be the suitable method to determine the ΔH for this example. Remember that Q is the measure of energy transferred in Joules. And this can be converted to ΔH by converting Q (J) into kJ/mol by taking into account the number of mol of hexane that was responsible for the energy transferred.
As Q takes into account M, the mass of water, an increase in the volume or mass of water will result in an increase in Q and thus resulting in a bigger ΔH value. In this example, a greater exothermic value will result.
For other scenarios, the different methods to directly determine the ΔH would include:
- Hess's Cycle
- Born-Haber Cycle
- Bond Enthalpy
- Enthalpy Profile Diagram, with calibrated y-axis
I wish you all the best with your studies.