Burning 2.5g of methylbenzene , c7H8 caused temp of 250cm^3 water to rise by 60 , calculate the enthalpy change per mole. How do I do this ?

Question

can anyone explain step by step including conversions to kjmol^-1 at the end 

Answer 1

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First, get the energy absorbed by the water:

q = (mass) (temp change) (specific heat)

q = (250 g) (60 C) (4.184 J/mol C)

q = 62760 J

Second, get moles of C7H8:

2.5 g / 92.1402 g/mol = 0.0271326 mol

Third, calc kJ/mol:

62.760 jJ / 0.0271326 mol = 2313.08 kJ/mol

Round off as you see fit. If you teacher insists on a sign on the enthalpy, then use a negative since the reaction was exothermic.