Question

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Answer 1

What a strange question. All the reactions that occur in an organism (or anywhere else) are spontaneous because, you know, they actually happen. "Non-spontaneous" is just a synonym for "things that don't happen," like water running uphill or a ball bouncing higher instead of lower. Stuff that violates the First or Second Law of thermodynamics. Obviously nothing takes place in a living organism that conflicts with the laws of thermodynamics.

I'm trying to figure out what the person who wrote this question really meant, but I'm not sure. Does he mean to draw a distinction between reactions that themselves increase entropy, or decrease it? Because some reactions are driven by the fact that they increase entropy -- and so fulfill the conditions of spontaneity laid down by the Second Law directly -- or because enthalpy is reduced, and the resulting exothermic heat flow increases the entropy of the surroundings. Also, some reacitons are better described as being driven by being coupled to other reactions. Many reactions that construct proteins and nucleic acids (and which therefore significantly reduce entropy themselves) are driven by being coupled to the hyrolyzation of ATP, which both releases significant heat and also increases entropy (so it's a very spontaneous reaction).

The entropy of an entire organism is difficult to assign, but arguendo we might think it remains largely constant over the lifetime of an individual, because we don't see many of the usual signs of increasing entropy -- higher temperature, lower density, liquids turning to gases and solids to liquids, more mixing of separate chemical species. For similar reasons the free energy, to the extent it can be defined at all, remains roughly constant.

But in both these cases our assertions are necessarily approximate and fussy, even sloppy, because organisms generally can't be considered isolated systems, or even systems like normal chemical reactions thar are just in contact with heat and pressure reservoirs. Organisms exchange matter, energy and volume with the enviironment all the time, so they are not closed. (The proper viewpoint is what's called the "grand potential," which is an unusual form of free energy useful for systems that allow matter flow to and from the environment.)

The fact that all the chemical reactions in the organism run is because the free energy of the organism PLUS local surroundings steadily increases, and ultimately because the entropy of the universe steadily increases.

Answer 2

Really. So how does he explain how water *spontaneously* freezes at 0C? Freezing involves a significant reduction in entropy, obviously.

Well, whatever. Sorry about that, but you need to work within whatever system you find yourself. Good luck.