Bellringer

If we applied kinetic-molecular theory to liquids and solids, how would you re-word the three basic assumptions of the theory?

Liquids and SolidsObjectives:

1. State the kinetic theory of matter.

2. Use the kinetic theory to explain states of matter.

The Kinetic-Molecular Theory

Def. (again!): describes the behavior of gases in terms of particles in motion

Can be applied to liquids and solids; however, you must also consider the forces of attraction between the particles. (What kind of forces are these?)

Liquids

Like gases, liquids take the shape of their container.

Unlike gases, the attractive (intermolecular) forces keep the particles closely packed (given liquids a fixed volume).

Behavior of Liquids:

Can liquids and gases of the same substance have the same temperature?

1. Density and Compression: Density of liquids is much greater than that of

gases, AT THE SAME TEMPERATURE AND PRESSURE.

Since KE (and temperature) is the same, what can account for the difference in density?

Liquids CAN be compressed, but not very much. Why not?

Behavior of Liquids:

2. Fluidity: ability to flow Both gases and liquids are considered fluids.

Why? Can a liquid diffuse? Which is more fluid, a gas or a liquid?

3. Viscosity: a liquid’s resistance to flow What do you think would affect (increase) a

liquid’s viscosity?

Behavior of Liquids:

4. Surface tension: Def: the energy required to increase the surface

area of a liquid by a given amount Particles in the middle of a liquid can be

attracted to particles to the side, above, and below them. What about the particles at the surface?

The stronger the intermolecular forces, the greater the surface tension.

Water Domes Mini-Lab

1. See how many drops of water you can get on the penny. (Drops must free fall!!!)

2. Dry off the penny and build a 20-drop water dome on it.

3. If you poke it with a clean, dry pin, does this break the cohesive (attractive) bonds b/t water molecules?

4. Dip the pin in liquid soap and poke the water dome. What happens?

5. How does soap affect surface tension? Propose an explanation for WHY.

Solids

According to kinetic-molecular theory, the kinetic energy of a mole of a solid substance is the SAME as a mole of the same liquid substance AT THE SAME TEMPERATURE.

So why does the solid have a definite shape and volume?

Answer: Strong intermolecular forces in the solid limit the motion of the particles to “vibrations around fixed locations”.

Solids, continued……

How does density of a solid usually compare to that of the same liquid?

Can solids be compressed? Are solids fluid?