Fluids and Physical Chemistry – Cool Interesting Facts

When we talk in terms of Physical Chemistry, a fluid is a substance that fills the container it is in. It has no regular structure, but the molecules that make up the fluid move randomly. The hotter it is, the faster they move. The vapor pressure increases above an open container until it is equal to one air, and then it starts to boil. When the temperature is less that the boiling point, you see a definite surface held there by surface tension. As it cools down, the molecules move less quickly and start to crystallize into a substantial.

All this depends upon the intermolecular forces, which are electrostatic, and are long ranged. These are usually called Van der Waals forces in the liquid phase. Sometimes the molecules have dipole moments and sometimes they do not. The former are called polar fluids and the latter are non-polar fluids.

Life depends upon us having liquid water. We believe that any other life in the Universe must have a liquid water ecosystem.

To here I have been talking about the usual fluids, like ammonia, water, benzene, etc, and these fluids have a definite temperature at which they freeze and boil. Like for water 0 C and 100 C. But if you look out the window, you are looking by glass.

Glass is truly a supercooled liquid (getting cooler!).

That method when you heat glass it does not suddenly melt, but starts to get soft and then softer, with no sharp melting point. These solids do not have a crystal structure. The have random orientations of molecules (Silicon dioxide usually), and are called amorphous (not amorous) solids.

Liquid Crystal characterize (LCD) are Liquids too.

But there are other types of liquids, like Liquid Crystals. You have them on watch dials and TV screens: Liquid Crystal characterize (LCD). They flow, so are fluids, but the molecules can all be oriented the same way too. They are in between a liquid and crystal. Because they have crystal structure, it is possible to apply heat or charge on a small area and this changes the arrangement (the phase) at that identify. Because light is distributed differently from the other regions, it appears different-it displays an image caused by the shape of the vicinity were the applied heat or charge is applied.

Then there is Mercury, quick silver, and a liquid. It is a heavy metal poison so do not touch it. All metals melt ultimately, it is just that Hg has a melting point much lower than other metals.

Cold Liquids for Cool Shows and Events.

How about really cold liquids? In concerts and theaters you often see a white mist. It is liquid Nitrogen, harmless when it evaporates because air is 80% N2. It is quite cold, minus 196 C, so when it evaporates into the air, it cools the air so the mist you see is water crystals halting out of the air.

The lowest boiling point of a liquid is Liquid Helium. Think of it. It is a small spherical atom (filled orbitals 1s2), so there are very small forces between them. They just roll over each other. It has a boiling point of 4.22 degrees above absolute zero. So it boils at 4.22 K = -268 C.

You have heard of superconductivity:–solids that have zero electrical resistance.

There are also superfluids. They have no viscosity but they have a surface tension like a liquid. They flow right up the sides of a container. Liquid Helium is an example of a superfluid.

I hope this gives a bit of an overview of the physics and physical chemistry of liquids.

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