Chapter 10 The Kinetic Theory of Matter

Pre-Class Question Look at the two containers of liquid. Which container has the greater volume of liquid? Look at the two balloons. Which balloon has the greater volume of gas?

Physical Behavior of Matter There is a close relationship between the physical state of a substance and its temperature. You will discover that the state of any matter is determined by the motion of its particles and the attractive forces between them.

States of Matter A solid is rigid with a definite shape. ▫ Solids are rigid because the atoms, ions, or molecules that make up a solid are fixed in place. A liquid is flowing matter with a definite volume but an indefinite shape. ▫ A liquid takes the shape of its container because the particles of a liquid can move and easily glide over each other. A gas is flowing, compressible matter that has NO definite volume or shape. ▫ The particles that make up a gas are much farther apart, so they can be easily pushed together.

The Kinetic Theory of Matter The constant, random motion of tiny chunks of matter is called Brownian motion. The kinetic theory states that submicroscopic particles of matter are in constant, random motion. ▫ The energy of moving objects is called kinetic energy.

Kinetic Model of Gases Gas particles do not lose kinetic energy when they collide with the walls of their container or with another gas particle. ▫ Each gas particle rebounds without losing speed but in a new direction. ▫ Collisions of particles in a gas are called elastic collisions because no kinetic energy is lost. A gas with particles that are in constant random motion but have no attraction for each other is called an ideal gas. ▫ Ideal gases undergo elastic collisions.

Kinetic Model of Gases Continued Except at very low temperatures or very high pressures, nearly all real gases behave as ideal gases. ▫ The kinetic theory explains why gases fill their container and why they exert pressure on the walls of the container. ▫ The gas particles move randomly in all directions until they strike the walls or other particles and bounce back.

Pre-Class Question Try to lift the mat off of the lab table in the back. Can you do it? What force is acting on the mat?

More on the Kinetic Model of Gases Pressure is the force acting on a unit area of a surface (the force per square centimeter). Earth’s atmosphere, which is a mixture of gases, exerts a pressure. ▫ Atmospheric pressure is caused by the constant bombardment of the molecules and atoms in air.

Kinetic Models of Liquids and Solids Interparticle forces in a liquid maintain their volume, but not their shape. ▫ The particles of a liquid can slide past each other, but they are so close together that they don’t move straight or smooth. Strong forces between particles explain the rigid structure of solids. ▫ This arrangement is called a crystal lattice. ▫ Particles of a solid cannot move past each other, but they bounce off of one another.

Other Forms of Matter Materials called liquid crystals lose their rigid organization in only one or two dimensions when they melt. ▫ Interparticle forces are relatively weak, and they can flow like a liquid when the lattice is broken. An amorphous material has a haphazard, disjointed, and incomplete crystal lattice. A plasma is an ionized gas. ▫ It can conduct electrical current, but it is electrically neutral.

Pre-Class Question Why is the air inside a hot air balloon heated?

Temperature and Kinetic Energy The temperature of a material is a measure of the average kinetic energy of particles. ▫ As temperature increases, kinetic energy also increases and vice versa. ▫ Could kinetic energy ever be zero?  The temperature at which a substance would have zero kinetic energy is called absolute zero. ▫ The Kelvin scale is defined so that the temperature of a substance is directly proportional to the average kinetic energy of the particles.

Temperature Conversions Kelvin to Celsius ▫ Celsius = Kelvin Celsius to Kelvin ▫ Kelvin = Celsius + 273

Mass, Speed and Kinetic Energy Two gases at the same temperature will have the same kinetic energy. If the gases have the same mass, then they will also travel at the same speed. If one gas is lighter than the other, the lighter gas will travel faster. Diffusion is the process by which particles of matter fill a space because of random motion. Heavier particles diffuse more slowly than lighter ones

Pre-Class Questions What is the freezing point of water? What is the melting point of ice?

Change of State Evaporation is the process by which particles of a liquid form a gas by escaping from the surface. ▫ The area of the surface, temperature, and humidity affect the rate of evaporation. ▫ Liquids that evaporate quickly are volatile. The process by which particles of a solid escape from its surface and form a gas is called sublimation.

Chang of State Continued Condensation is the process of gas particles coming closer together (condense) and form a liquid. The pressure of a substance in equilibrium with it’s liquid is called its vapor pressure. ▫ Volatile substances have high vapor pressures. ▫ The boiling point of a substance is the temperature of a substance when its vapor pressure equals the pressure exerted on the surface of the liquid (atmospheric pressure).

Heat Energy The energy absorbed when 1 kg of a liquid vaporizes at its normal boiling point is called its heat of vaporization. ▫ The joule is the SI unit of energy. ▫ Burns from steam are usually more severe than burns received form hot water. This is because the steam transfers a great deal of heat to the skin when it condenses.

Heat Energy The melting point is the temperature of the solid when its crystal lattice begins to fall apart to become a liquid. The temperature of a liquid when it begins to form a crystal lattice and becomes a solid is called its freezing point. ▫ The energy released as 1 kg of a substance solidifies at its freezing point is called its heat of fusion.