# Is osmosis a thermal machine?

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1. Mar 24, 2016

### larsa

I have read that osmosis " works like a machine ". It lifts weight ( this is obvious ) on the expense of thermal energy.

Does anyone has any thoughts about how it consumes thermal energy?

2. Mar 24, 2016

### Staff: Mentor

Could you give a reference for that?

I don't see how this can be correct. Osmosis is based on a difference of chemical potential, not temperature. I wouldn't know how to qualify the kind of energy it consumes, but it is not thermal, nor chemical (in the usual sense of that word).

3. Mar 24, 2016

### larsa

Thanks for your answer. I don't remember the text where i met this expression but per example the hyperphysics article defines osmosis as a diffusion process driven by internal energy and internal energy is defined as energy associated with random motion of molecules.

That is something like thermal energy if i understand what i read.

4. Mar 25, 2016

### Kevin McHugh

Osmosis is a pressure gradient, caused by chemical potential. Think potassium and sodium.

5. Mar 25, 2016

### larsa

When you have time, could you explain what you mean?

6. Mar 27, 2016

### 256bits

I don't know what you mean by "consumes thermal energy."
But anyways, yes osmosis can be considered as being a phenomenom of thermodynamics.

If you take the ideal gas equation, PV=nRT, and arrange it just a bit, you get,
P=(n/V)RT

Replace P with π, and n/V and you get the osomotic pressure equation
π = cRT, where c is the concentration of the solute in moles per liter.

You can read some discussion here,
http://urila.tripod.com/osmotic.htm

7. Mar 27, 2016