Are all suspensions, emulsions and foam thermodynamically unstable?
Can you be more specific? Essentially all matter is thermodynamically unstable; the total entropy of the universe would be higher if all the atoms in my body were dispersed throughout the cosmos. The same thing applies to a suspension, for example.
The way we deal with this problem is to talk about an isolated system, a control volume, so we only need to consider the components of the suspension. But even here, a dispersed suspension is unstable if it would settle given enough time. A foam is unstable if it would eventually collapse.
But perhaps we're looking at time scales on the order of seconds. In that case, if the suspended phase has reached chemical equilibrium with the solvent, we might consider it to be thermodynamically stable (at least, for that time scale and that system definition). Does that make sense?
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