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States of Matter - Concept

Teacher/Instructor Jacqueline Spivey
Jacqueline Spivey

Ph.D.,U.C.Santa Cruz
Teaching at a top-ranked high school in SF

She teaches general and chemistry at a top-ranked high school in San Francisco. Prior to that, she lead and published a number of research studies and lectured at SF State University.

States of matter are the different phases which matters can take - gas, liquid and solid. Gas has no fixed shape and conforms to the volume of its container. A liquid has a distinct volume but assumes the shape of its container. A solid has definite shape and volume, regardless of its container. In the case of H20 steam is a gas, water is a liquid and ice is a solid. Most substances are more dense in their solid form, but water is an exception.

So let's go ahead this segment and discuss the different states of matter. So before we get started let's remind ourselves what matter is, and matter is anything that takes up space. So it can exist either as a gas, as a liquid or as a solid. So let's go through how gases, liquids and solids differ fundamentally.

So gas has no fixed volume or shape and it conforms to the shape of its container. And we can also think of gas as a vapor. And it can be compressed or it can expand depending on what the volume size is. So in a smaller container it can be compressed, if the container is larger then it will expand.

So a liquid has a distinct volume that's independent of it's container but it has no specific shape. So it will assume the shape of whatever container it is put in. So liquid cannot be compressed, unlike a gas.

And then you have solids which have both definite shape and volume and definitely cannot be compressed. So how do you know what state the matter is going to be in? So the state of a given sample of matter depends on the strength of the forces among the particles that are actually contained in the matter. So it'd be specific to whatever system it is that you're talking about.

So, briefly let's look at these pictures and see if that will help a little bit for you to be able to distinguish the behaviors of a gas, of a liquid and of a solid. So let's look at water. So basically, if water is in a gas or in the liquid, I mean the vapor phase, it's air and so when molecules are in the gas phase they're far apart and they're moving at high speeds, interacting and colliding with both each other, and their container. Okay, so far apart, lots of collisions, interacting all over the place.

And then when it becomes a liquid, say water, then the molecules become packed closer together, they're still moving rapidly which allows them to slide over each other. So that's why liquids pour easily. And then when something becomes a solid, say in this case ice, then they're packed together more densely and they're held tighter together and they're definitely in fixed arrangements. So I urge you again to look at some other systems and see if you can distinguish the difference between the solid form, the liquid form and the gas form. And that's states of matter.