Greetings everyone! I have been a long-time lurker on here and have just recently signed up. I'm unsure if this was the correct forum to post this in, so I apologize in advance. My question isn't exactly homework per se - I am currently studying for my MCAT and have been trying to wrap my head around a particular concept recently; I would love it if any of your bright individuals out there could share some insight. 1. The problem statement, all variables and given/known data For a reaction that is non-spontaneous at ALL temperatures (dH is positive and TdS is negative), can this ever actually occur? (Thermodynamically speaking). Furthermore, if you were to HYPOTHETICALLY couple such a reaction in a living system (say to ATP or an even higher energy carrier such as cAMP), or in vitro to something of a similar nature, would this reaction (non-spont at all T) occur or not occur even if the combined delta G of the coupled reaction turned out to be negative? (i.e. [positive delta G of the rxn that is non-spont at all T] + [negative delta G of the highly spont. 2nd rxn] = negative overall delta G). 2. Relevant equations dG = dH - TdS 3. The attempt at a solution I want to say that a reaction which is non-spontaneous all temperatures will never occur (thermodynamically), as no amount of energy addition will allow this process to occur. But then if it is coupled to a highly exergonic reaction, in which the total delta G for the overall reaction becomes negative (thus spontaneous), the math says it should occur, but from the statement above, it shouldn't? Or does coupling completely override the non-spontaneity condition at all temperatures for the first reaction, whereby the coupled reaction is now considered a completely separate reaction with its own associated enthalpy change and entropy change?