When you’re boiling a pot of water, right before the water starts to boil if you watch carefully at the bottom of the pot there will be tiny bubbles that form and disappear. Why do they just disappear instead of floating up to the top once they’re already formed??
In: Physics
I’m a materials engineer so here goes.
Water boiling is a phase change reaction. In any phase change there has to be nucleation of the new phase in the current phase.
Nucleation basically means small (sometimes spherical) bubbles of the second phase trapped in the first.
Since all reactions are governed by kinetics and thermodynamics both, it is possible that a reaction may be thermodynamically favorable but not kinetically.
This means, right before the water boils, it has enough energy to turn into vapor, but it does not have enough to escape the liquid
Also, there is a critical nucleation size, beyond which the second phase is stable in the first one. This is due to the different internal and surface energies of the 2 phases.
Simply, when 2 phases are in contact, they have some surface energy. Both phases also have some internal energy.
Both these energies are negative (so higher means more negative)
If the surface energy is higher than the internal energy, the nucleus will be stable and grow. OTOH, if the surface energy is lower, the nucleus will collapse.
Again, kinetics says the reaction should probably happen, since we have enough energy to grow a nucleus. But until thermodynamics comes in and says “you have crossed the critical nucleus size, you may grow further,” the nucleus will always collapse on itself
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