Do all the molecules or atoms in a liquid have about the same speed, or much different speeds?

1 Answer
Aug 4, 2017

For condensed phases only, practically the same speed or with minor differences... assuming no outside influence from energy (or other forces).


We can usually assume that the particles in a pure condensed substance (for simplicity) are moving at uniform speeds (i.e. they're similar throughout the medium). This assumes no forces/energy is influencing the matter.

An exception is the moment when matter is being heated/cooled up/down (motion increases/decreases respectively).

For example, if we were to look at a liquid first being boiled from the bottom, the bottom of the container would contain hotter liquid (faster-moving particles) than particles near the surface (slower-moving, and not as hot).

Considering that this process is not instantaneous, meaning the process is gradual, the speeds between different particles will alter for an appreciable amount of time.

In conclusion, if no external influences are present, then the particles in a condensed phase (liquid, in this case) would have similar speeds. Only while heating up/cooling down the matter would the particle motion change, AND if the change is gradual, an energetic equilibrium will eventually establish itself.