Video Transcript
A substance can exist as a solid,
liquid, or gas. In which of the states of matter do
particles in the substance have the most energy?
One great example of a substance
that can exist as a solid, a liquid, or a gas is water. We know that water can exist as a
chunk of ice, that is, a solid. Or it can exist as a liquid, just
water. Or it can exist as water vapour, a
gas. What we want to know is in which of
these states of matter, solid, liquid, or gas, do the particles in our substance
have the most energy.
To figure that out, we can consider
just how it is that water moves from being a solid to being a liquid to being a
gas. For example, considering the
transition from solid to liquid, we know that if we leave an ice cube out on a
counter, eventually it will melt. It will become a liquid. That happens because heat from the
environment is added to the ice cube. If we wanted to, we could speed up
this process by putting the ice cube in a dish and heating the dish. This shows us that, in order to go
from a solid to a liquid, we need to add energy to our substance.
And the same is true in going from
a liquid to a gas. If we heat up water in a pan, then
eventually, the water will start to boil. That is, it will vaporize. Just like before, we’re adding
energy into our substance, which is changing its state now from a liquid to a
gas. From this perspective, we would
guess that the particles in the gaseous state of our substance have the most
energy.
Another way to see this is to think
of it in terms of the average speed of the particles in each state of matter. When our substance is a solid, the
particles in it are arranged in a very orderly fashion. They don’t move quickly at all. But then, as we add energy to our
substance, the average speed of the particles picks up. The average particle speed in a
liquid is higher than that in a solid. And higher still as we might be
able to see from the sketch is the average speed of the particles in a gas compared
to that in a liquid.
Both of these perspectives indicate
the same answer to this question. They both tell us that the state of
matter in which a material has the most energy is the gaseous state.
