[Ankesh]

              Electric arc
N2   +   02        2NO   This is an endothermic reaction.
               3500 C

Now, its reverse,

2NO        N2 +02  This is also an endothermic reaction.
         900 C

How can a reaction and its reverse both be endothermic??

[sjb]

Different temperatures?

[cliverlong]

How can a reaction and its reverse both be endothermic??

Interesting example. I would have thought it was impossible. Where did you get your data from?
Sjb observation about the possible effect of temperature is interesting.

[Ankesh]

please someone explain this question
These reactions are defying all principles of thermodynamics.

@sjb,
indeed they are at diff temp. but still they are enothermic.

[Borek]

please someone explain this question
These reacns r defying all principles of thermodynamics.

@sjb,
indeed they r at diff temp. but still they r enothermic.

Please read forum rules. Official forum language is English.

[Ankesh]

sorry,edited it now
But please answer the question.

[sjb]

Sjb observation about the possible effect of temperature is interesting.

Here is my thought process

What determines whether a reaction is feasible?  :delta: G, right?

 :delta: G =  :delta: H - T :delta: S

Whether a reaction is endo- or exothermic depends on  :delta: H, rather than :delta: G. Presumably at high enough temperatures the T :delta: S term dominates, so the reverse reaction is feasible cf H₂  2H, which lies to the left on Earth, but more to the right on the Sun, for instance

Comments welcome

[nj_bartel]

I agree sjb.  It would be possible for them to both be endergonic as well.  You have to have constant temperature to have a comparison.

[Ankesh]

Even if it is endergonic,
The transformation is occuring at constant temp. and pressure.
So, :delta: G > 0
These reactions have a very negligible entropy change.(no. of gaseous moles is same on both sides).So, even if temp is very high, contibution of T :delta: S alone would ot be sufficient for  :delta: G >0
So, the reactions have to be endothermic.