Work from a spontaneous endothemic reaction

[Olfaction]

Hello, could someone please help me with this?

Some reactions are spontaneous (with dG < 0) although they are endothermic (dH > 0). My question is:

Is it possible to extract work from such a reaction? The process I understand to produce work  is to heat something in a contained space and transfer the heat pressure into kinetic energy with a turbine. (Sorry I know this is not very formal).

For example, this reaction is a spontaneous endothermic reaction.

NH₄NO₃ (s)   –>   NH₄⁺ (aq) + NO₃^- (aq)

Is there a way I can get my turbine to work with this reaction? Is the Gibbs Free Energy that comes from the raise in Entropy of any use? And how so, if I get not heat?

Thank you for you help. I am quite confused.

[Bufofrog]

The reaction requires heat, so the reaction cannot be used to run a turbine.  The reaction cools down the the solution.

[Olfaction]

But why is it called Gibb's free energy, if there is no way to use it? Is there maybe a way to create some gradient and do some diffusion that could be harnessed into work, altough no heat is being produced?

[exchemist]

1 hour ago, Olfaction said:

But why is it called Gibb's free energy, if there is no way to use it? Is there maybe a way to create some gradient and do some diffusion that could be harnessed into work, altough no heat is being produced?

I’m rusty on this but I should have thought you can get work out of a process with -ve change in G. For instance you could have an electrode potential in a suitable electrochemical cell, even if you could not run a heat engine. 
 

If you did find a way to extract work, I think the enthalpy change would become even more -ve, to balance the books.

But I’m very much open to correction on this.

[Olfaction]

Oh thanks, that’s the kind of answer I was expecting. That would explain why the Nernst-Equation allows me to convert redox potential into Gibbs Energy and not into Enthalpy…

ΔG = -z F ΔE    

Where G ist the molar Gibbs Free Energy, z the number of exchanged electrons and E ist the standard redox potential…

[exchemist]

27 minutes ago, Olfaction said:

Oh thanks, that’s the kind of answer I was expecting. That would explain why the Nernst-Equation allows me to convert redox potential into Gibbs Energy and not into Enthalpy…

ΔG = -z F ΔE    

Where G ist the molar Gibbs Free Energy, z the number of exchanged electrons and E ist the standard redox potential…

That's what I had in mind. But let's see if someone jumps in and tells me I'm quite wrong.........  

[Olfaction]

Like know you these plastic packs you crack and they get cold?

I read that it is often this spontaneous endothermic reaction taking place.

NH₄NO₃ (s)   –>   NH₄⁺ (aq) + NO₃^- (aq)

So, with well-suited electrochemical chamber, I should be able to create current until the reaction reaches equilibrium?

Oh wait, because of  ΔG° =  ΔH° - TΔS° , this reaction will only be spontaneous at high temperatures. So isn’t it simply, that if we create a cold spot in a warmer environment, there is going to be a flow of molecule to fill the hole and therefore kinetic energy? 

[KJW]

7 hours ago, Olfaction said:

Is there a way I can get my turbine to work with this reaction? Is the Gibbs Free Energy that comes from the raise in Entropy of any use? And how so, if I get not heat?

You could use the endothermic reaction as the cold sink of a heat engine, with room temperature being the hot source.