Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: MilkyCar on April 23, 2023, 02:20:32 PM
-
I'm confused and I've been trying to solve this problem.
So it states that given the following data:
C2H4 (g) + 3O2 (g) -> 2CO2 (g) + 2H2O (l) H= -1411.0 kJ
2C2H6 (g) + 7O2 (g) -> 4CO2 (g) + 6H2O (l) H = -3119.8 kJ
2H2 (g) + O2 (g) -> 2H2O (l) H = -571.7 kJ
And I have to calculate H for the reaction:
C2H4 (g) + H2 (g) -> C2H6 (g)
I didn't change anything for equation one and then I did -1411.0 - -3119.8 + (-571.7) and then I divided the answer by 2 to get 568.6 kJ. I am stuck and I'm unsure how to get the right answer.
-
Sum of rectants minus sum of products.
Substitut C2H4 + H2 => C2H6 to the given equations.
You take the first equation how it is for C2H4.
For H2 you have to take the building of water by half and for C2H6 you also have to subtract the second equation by half.
-
Okay, I tried that and I got -137.0 kJ as a result. Is this correct?
-
Its correct
-
Assuming I made no typos, you took first equation, subtracted second and added third, yes?
C2H4 + 3O2 :rarrow: 2CO2 + 2H2O
- (2C2H6 + 7O2 :rarrow: 4CO2 + 6H2O)
+ (2H2 + O2 :rarrow: 2H2O)
--------------------------------------------
C2H4 + 3O2 - 2C2H6 - 7O2 + 2H2 + O2 :rarrow: 2CO2 + 2H2O - 4CO2 - 6H2O + 2H2O
sorting
C2H4 - 2C2H6 + 3O2 - 7O2 + O2 + 2H2 :rarrow: 2CO2 - 4CO2 + 2H2O - 6H2O + 2H2O
combining
C2H4 - 2C2H6 - 3O2 + 2H2 :rarrow: -2O2 - 2H2O
moving things with negative coefficients to other side
C2H4 + 2H2 + 2CO2 + 2H2O :rarrow: 2C2H6 + 3O2
Is the final equation the one you are looking for?
-
No
C2H4 + 3 O2 => 2 CO2 + 2 H2O -1411 kJ
Convert first
C2H6 + 3,5 O2 => 2 CO2 + 3 H2O -1559,9 kJ
C2H6 = - 3,5 O2 + 2 CO2 + 3 H2O
and H2 + 0,5 O2 => H2O - 285,85 kJ
H2 => H2O - 0,5 O2
C2H4 + 3 O2 + H2 - 3,5 O2 + 2 CO2 + 3 H2O => 2 CO2 + 2 H2O + H2O - 0,5 O2 + C2H6
C2H4 + H2 => C2H6
-1411 kJ + (-285,85 kJ) -(-1559,9kJ) = 136,95 kJ