Calculate the heat combustion for C2H6 from the following information?

Question

C2H4 3O2 -> 2CO2 2H2O Delta Hr = -1409.5KJ

C2H4 H2 -> C2H6 Delta Hr = -136.KkJ

H2 ½ O2 -> H2O Delta Hr = -285K kJ

If someone could help me with this question i'd greatly appreciate it :)

Answer 1

(A) C2H4 & 3O2 -> 2CO2 & 2H2O .....Delta H = -1409.5KJ

(B) C2H4 & H2 -> C2H6    .......   ....   Delta H = -136.KkJ

(C) H2 ½ O2 -> H2O   ....   ....    .....   Delta Hr = -285K kJ

need C2H6 & 3.5 O2 --> 2 CO2  & 3 H2O

if you reverse (B) & combine it with (A) & (C) you get what you need: C2H6 & 3.5 O2 --> 2 CO2  & 3 H2O (everything else cancels out)

so -B's dH & plus A's dH & plus C's dH gives you the energy you want:

+136  & -1409.5 & -285 = -1558.5

your answer is -1558.5 kJ

but you might consider rounding off to -1559 kJ, since "-136" wasn't "-136.0"