Kinetic Theory & the States of Matter Chapter 16.1 Notes

The Kinetic Theory Kinetic theory is an explanation of how particles in matter behave.

The Kinetic Theory There are 3 assumptions about kinetic theory are: 1.All matter is made up of small particles (atoms, molecules, and ions) 2.These particles are in constant, random motion. 3.These particles are colliding with each other and the walls of their container at all times.

The Kinetic Theory To visualize Kinetic Theory, think of each particle as a tiny ping-pong ball constantly moving. These balls are bouncing and colliding with each other. Atoms in solids are held tightly in place by the attraction between the particles.

The Kinetic Theory This attraction between the particles gives solids a definite shape and a definite volume. However; the thermal energy in the particles does cause them to vibrate in place.

The Kinetic Theory When the temperature of a substance is lowered, the particles will have less thermal energy and will vibrate more slowly.

Different States of Matter There are 3 states of matter: 1.Solids 2.Liquids 3.Gases

Solids An ice cube is an example of a solid. The particles of a solid are closely packed together and form an organized, geometric arrangement. Remember, the particles in a solid still contain some kinetic energy so they are vibrating in their fixed positions.

Solids If you place the ice cube into hot soup, the particles of the hot soup are moving around and will collide with the surface particles of the ice cube. If they gain enough kinetic energy to overcome their attractive forces between the solid particles, the particles will slide apart and out of their ordered arrangement and the ice melts.

Solids The temperature at which a solid begins to liquefy is known as the melting point. The amount of energy required to change a substance from the solid phase to the liquid phase at its melting point is known as the heat of fusion for that substance.

Liquids The particles of a liquid move more freely than the particles of a solid. They have more kinetic energy than the solid. A liquid’s particles can slide past each other, which is what allows a liquid to flow and take the shape of it’s container. There is still attraction between the particles of a liquid, which cause them to continue to cling together, giving liquids a definite volume.

Liquids A liquid can become a gas several different ways. All the ways involve a gaining of kinetic energy to escape the attractive forces of the liquid. Vaporization includes the processes of both evaporation and boiling.

Liquids Evaporation only occurs at the surface of the liquid and can (and often does) occur below the substance’s boiling point. Boiling occurs throughout the liquid at a special temperature called the boiling point. Every substance has it’s own unique boiling point. Water, for example, has a boiling point of 100 °C or 212 °F.

Gases In gases, the particles are far apart and the attractive forces between the particles are gone. Gases do not have a fixed volume or shape. Therefore, they can spread far apart or contract to fill the container their in.

Gases Diffusion is the spreading of particles throughout a given volume until they are uniformly distributed. This occurs in solids and liquids, but it occurs most rapidly in gases. By diffusion, gases will move in constant random motion to fill their container evenly, even if the container is a room.

Solid or Liquid? There are two types of substances that cannot be classified as a solid or a liquid because they are kind of like both. 1.Amorphous solids 2.Liquid crystals

Solid or Liquid? Amorphous Solids First, amorphous solids are substances that lack the highly ordered structure found in solids and crystals. (Examples: wax, candles, plastics, and glass) They do not melt at an exact melting point, but soften gradually into a liquid.

Thermal Expansion Thermal expansion occurs in all states of matter: solids, liquids, and gases. Have you ever noticed the seams in a concrete driveway or sidewalk? These separation lines are called expansion joints. –When the concrete absorbs heat, it expands. Then when it cools, it contracts. –If these expansion joints aren’t used, the concrete will crack when the temperature changes.

Thermal Expansion The kinetic theory can be used to explain this behavior in concrete. –Particles move faster and separate as the temperature rises. –This separation of particles results in an expansion of the entire object known as thermal expansion.

Thermal Expansion Kinetic Theory explains the contraction in objects too. –When the temperature of an object is lowered, particles slow down and the attraction between the particles increases, so they move closer together. –This causes an overall shrinking of the object known as contraction.