C.Y.U. 4.12

1) The following table indicates how each property changes with temperature:

Note the opposite effect and the shared characteristics of density, viscosity and buoyancy.

Think about your life experiences and the kinetic molecular theory.

You know that when chocolate goes from a solid to liquid state, heat has been added.

When the heat energy expires, the chocolate starts to solidify.

What is happening to the molecules? Expansion? Contraction? Vibration? Patterns?

2) Solids have mass and a definite volume. They take up their own space. The density of the particles making up the mass of a solid is the greatest of the 3 states of matter.  The particles of a solid have strong forces of attraction and are locked into a rigid structure (a lattice-like pattern).

Liquids also have mass and a definite volume, but they take the shape of whatever container they are in. Liquids are less dense because the energy the particles have gained, causes them to move faster, further apart and free from the forces of attraction holding  them in one place. Particles slide past each other. The density of the particles making up the mass of a liquid is less than that of a solid and more than that of a gas.

Gases also have mass, but they have an indefinite volume. Gases disperse to fill the shape of whatever container they are in. The density of the particles making up the mass of a gas is the lowest of the three states of matter. Gas particles have gained so much energy that they have moved very far apart.

*Special Note

When referring to density in these comparisons it is important to note that any solid is not denser than any liquid – there is a large variety in the density of liquids (e.g. liquid mercury).

3) As the temperature of the cooking oil increased, the particles making up the oil gained more energy and vibrated faster. As the temperature rose, the forces of attraction between the particles became weaker, leaving larger spaces between them. This decreased the resistance that the oil had to flowing, resulting in decreased viscosity.

4) Water becomes less dense as a gas at 100° C like all other elements do. At 0° C water also drops in density – no other liquid does this.

5) Oxygen is stored as a liquid rather than a gas because it is more dense as a liquid. Thus more mass (oxygen) can be stored in a smaller volume. This saves space on an aircraft.

6) The temperature of tropical water is higher than that of water in temperate zones. Tropical water has a lower density than temperate zone water. The buoyant force exerted by tropical water is therefore lower, causing ships to float lower than in colder water.

7) Examples of substances changing changing temperature in the natural world include:

The cooling of molten lava and hot water shooting out of the vents in the ocean floor.

Lava is molten rock. Molten rock cools and becomes more viscous and dense with a decrease in temperature.

Steaming sea water heated to approximately 350° C comes out of the vents in the ocean floor, near zones of volcanic activity. This super heated water has low density and viscosity. The water rises and radiates in a convection-like current until it cools and falls back down to the ocean floor.

http://www.youtube.com/watch?v=XotF9fzo4Vo (hydrothermal vent – Nat. Geo)