Heat = -0.21 x 4.18 x 10^3 x 65

= 57.057 KJ

I then divided this value by 2, because it said half the heat was lost to the environment.

Therefore, Heat = 28.5285

As HoC = Heat on moles

Therefore ; 1367 (given) = 28.5285 divided by m/(12.01 x 2 + 1.008 x 6 + 16)

Mass of Ethanol = 0.96 g (2.d.p.)