Using Hess's law and equations 1-3 below, find delta H at 25 degree for the oxidation of C2H5OH(l).?

Question

1. C2H4(g)+3O2(g)-->
2CO2(g)+2H2O(l) deltaH= -1411kJ

2. C(graphite)+3H2(g)+(1/2)O2(g)-->
C2H5O2 deltaH= -278 kJ

3. C2H4(g)+H2O(l)-->
C2H5OH(l) deltaH= -44 kJ

final: C2H5OH(l)+3O2(g)-->
3H2O(l)+2CO2(g)

I can't figure out how to cancel the second equation because there is a single C and H2 there.Can anyone explains please?step by step solution please.Thank you.

I know it is little weird ..but the product of the equation is under the reactant..and i do that because it seems like some parts of the equation is not seen if i type the whole thing on the same line or something..please help.thank you

Recorrect equation #2

C(graphite)+3H2(g)+(1/2)O2(g)
-->C2H5OH(l) deltaH= -278kJ

this is the correct one

Hey..so is that mean I can just ignore equation #2?I don't have to use all the equation in this case?can anyone explains more please?=)

Answer 1

you don't need the second equation to solve the problem

all you need is first equation add negative third equation since you need the reverse equation

anyway, C2H4 cancel out, and you are left with the final equation

so (-1411KJ) + (44KJ) = (-1367KJ)


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well it would appear that the second equation is the "standard formation" for C2H5OH
you could find the enthalpies for the final reaction by using the "standard enthalpy formation" too, if you been taught of that

ps. a lot of question has more information than you need to through you off, so you need to find what you need in order to do the question, especially in chemistry, believe me, I learn it the hard way......

Answer 2

Hess Law Equation

Answer 3

C2H4+3O2 --> 2CO2+2H2O -1411

C2H5OH --> C2H4+H2O -44

The C2H4's cancel so you are left with what you want so just add the delta H's

it would appear that we don't need that 2nd equation

Answer 4

Recheck your equations; something's no longer accurate. you've were given 2N2O(g) which looks to have magicked itself faraway from the perfect equation. you've typed out a compound or 2 incorrectly.

Answer 5

yeah i hate chemistry but somehow i got stuck with it this year... Can't you also switch signs/sides w/ hess's law? i usually just figure it out through trial and error or look in the back of our old AP book for the answers :)