The Four Phases of Matter n There are four phases, or states, of matter. ¶ Solid- · Liquid ¸ Gas ¹ Plasma

Kinetic Theory n The states of matter are controlled by the kinetic molecular theory, which proposes that tiny particles (atoms) are in constant motion. n The more energy the particles have the faster they move and the more they spread out.

Kinetic Theory n Solids, liquids, and gases are classified based on the motion of molecules (kinetic theory). n Solids molecules are slow and close together. n Liquid molecules are faster and not as close. n Gases are very fast and spread out.

Solids n Solids have a definite shape and volume. n The atoms in a solid are tightly packed so the solids retain their shapes. n The movement of atoms is through vibrations. n Crystalline solids are made up of regular, repeating patterns of atoms, or crystals. Ex. Salt. n Amorphous solids can lose their shapes as particles flow around one another. Ex. Silicone rubber.

Liquids n Liquids have no definite shape but have a definite volume. n The atoms are tightly packed but not as tightly packed as solids. This is why liquids can be poured. n Some liquids pour more easily than others. Water is easier to pour than motor oil. n This is due to the liquid’s viscosity, or resistance to flow. n Glass is a highly viscous liquid.

Gas n Gases have neither definite shapes nor volumes. n Gases fill all the space of a container regardless of size. n The atoms in gases are spaced very far apart. n The spacing allows gas atoms to move freely and rapidly. n Because there is so much space between atoms we can compress gases. Inflating your tires is one example.

Plasma n Plasma is a high energy state of matter. n It is rare on earth, but one of the most common phases in the universe. Ex. Sun, stars. n Plasma is dangerous to living things n Plasma can’t be contained by ordinary matter, we have to have powerful magnets. It may be a future energy source.

Changes in State n Whenever a substance changes from one state of matter to another state it is said to undergo a phase change. n A solid changes into a liquid during melting. n In freezing, matter changes from the liquid state to the solid state.

Changes in State n The change from the liquid state to the gas state is called vaporization. n When a liquid vaporizes at the surface, and at temperatures below the boiling point, evaporation is occurring. n When you add heat to a liquid until it reaches a temperature at which it changes to gas below the surface, boiling occurs.

Changes in State n When a gas changes to a liquid, condensation is occurring. n We can also change from a solid directly to a gas without first becoming a liquid. This is sublimation. n All phase changes can be explained by the kinetic theory of matter.

Phase Change Diagram n

Heat of Fusion n The amount of heat energy needed to change a material from the solid state to the liquid state is the Heat of Fusion for that material. n For water the heat of fusion is 334 kJ/kg. This means it takes 334 kJ of energy to change 1 kg of water from ice to liquid water.

Heat of Vaporization n The amount of heat energy needed to change a liquid into a gas is the Heat of Vaporization of that material. n The heat of vaporization for water is 2260 kJ/kg.

Temperature and Phase Change n It is important to remember that during a change from one state to another the temperature remains the same. n After the phase change the addition of heat energy will result in an increase in temperature. The removal of heat energy will result in a decrease in temperature.

Pressure n The force of particles of gas in constant motion collides with the inside walls of a container. n The total amount of force exerted by the gas depends on the size of its container. If the container is small the amount of force is larger than if the container is big.

Pressure n The amount of force exerted on the walls per unit of area is called pressure. n P=F/A. The units for pressure are pascals (Pa). This unit is very small, so most pressures are given in kilopascals (kPa). n The pressure of the atmosphere pressing down on the Earth is 101.3kPa

Gas Laws n The gas laws allow us to describe the behavior of gases with changes in volume, temperature, and pressure.

Boyle’s Law n Boyle discovered that at a constant temperature the doubling of the pressure on a gas reduced its volume by half. n For example, if the temperature does not change, from say 20 o C, if the pressure of a gas changes the volume will change proportionally. n This is an inverse proportionality.

Charles’ Law n Charles discovered that when gases were heated through the same temperature interval, they all expanded the same amount. n He found that if the pressure were kept constant, raising the temperature of any gas from 0 o C to 1 o C increased the volume of the gas by 1/273 times the original volume.

Charles’ Law n The same relationship exists for cooling a gas. n Charles showed that the temperature of a gas and its volume were directly proportional. This means doubling the temperature of a gas doubles its volume and vice versa.

Charles’ Law n Using his law, Charles was able to calculate the temperature at which a gas would have a volume of zero. The kinetic theory says this should be the temperature at which all molecular motion stops. Charles found this temperature to be -273 o C, or 0K. This is also called absolute zero.

Buoyancy n Have you ever floated quietly in a pool? You seem weightless. However, as you climb out of the pool you feel as if you gain weight. The farther you climb out, the more you have to use your muscles to support yourself. While in the pool you were experiencing buoyancy, the ability of a fluid to exert an upward force on an object immersed in it.

Buoyancy n The upward force is called the buoyant force. n If the buoyant force is less than the object’s weight, the object will sink. If it is more the object will float. n According to Archimedes, the buoyant force is equal to the weight of the fluid displaced by the object.

Archimede’s Principle n When you drop an object into a fluid the object moves some of the fluid out of the way as it begins to sink. It only pushes fluid out of the way until the weight of the fluid moved is equal to the weight of the object. At this point the object will float. If the weight of the fluid never equals the weight of the object, the object sinks.

Pascal’s Principle n Pascal found that the pressure applied to a fluid is transmitted unchanged throughout the fluid. n This is how the brakes on your car work. When you step on the brakes you apply pressure to the brake fluid. This pressure is transmitted unchanged throughout the fluid to the brake pads.

Bernoulli’s Principle n According to Bernoulli, as the velocity of a fluid increases, the pressure exerted by the fluid decreases. n Airplane wings make use of this principle. The wings are thicker at the front. This makes the air have to travel faster to go over the top of the wing. The air over the top and bottom must go the same distance.

Bernoulli’s Principle n The air must go over the top and bottom and reach the other end at the same time. In order to go different distances in the same time, the air must travel faster over the top. Since it goes faster there must be less pressure on top so the airplane is lifted up. n Baseball pitchers also use Bernoulli’s principle. How?