I will calculate the change in enthalpy of combustion of 1.12g of hexane.
1) Calculate the energy transferred to 200g of water using the equation: J = mass of water in grams (200g) x specific heat capacity of water (4.18 J/gK) x temperature increase in Kelvin (24C = 297.15K). This results in the amount of energy transferred to the water of a total of 248,417.4J or 248.4kJ.
2) Calculate number of moles of hexane burnt using n=m/M. Weight of hexane before experiment = 222.07g. Weight of hexane after experiment = 220.92g. Therefore 1.15g of hexane was burnt during the experiment. 1.15g of hexane = 0.013mol of hexane.
3) Find enthalpy change of reaction. Combustion of 1mol of hexane produces (by my calculations) -4194 kJ/mol. Therefore, 0.013mol will produce (0.013/-4194) -3.1x10-6 kJ/mol.
So this is the procedure that I used to find out the answer! Was it correct? Because, apparently, you can use the values of steps 1 and 2 to find out the enthalpy change?