finding the mass of hexane required?

Question

Using a molar heat of combustion of hexane (C₆H₁₄) –4163 kJ/mol, the mass of hexane required to increase the temperature of 1.76 L of water from 21.0°C to 70.0°C is a.bc? g. 

Put your answer for a.bc in grams. 

Answer 1

q = mCT

q = heat = ?

m = mass of water = 1.76 L x 1000 g/L = 1760 g (assuming a density for water of 1.0 g/ml)

C = specific heat of water = 4.184 J/g-deg

∆T = change in temperature = 70.0º - 21.0º = 49º

q = (1760 g)(4.184 J/g-deg)(49 deg) = 360,828 J of heat needed = 360.8 kJ

360.8 kJ x 1 mole hexane/4163 kJ = 0.0867 moles hexane needed

0.0867 moles hexane x 86.2 g/mole = 7.47 g hexane required