1 mol etena degaja ΔrH = -1389 kJ (din date termodinamice)
niu = masa / miu
miu C2H4 = 24+4 = 28 g/mol
=> niu = 12,5/28 = 0,45 moli etena
1 mol .................. -1389 Kj
0,45 moli .............. a = -620 Kj