Chapter 13 States of Matter Read pgs

Kinetic Molecular Theory The kinetic molecular theory describes the behavior of gases in terms of particles in motion. – A. Gases consist of point-masses. No volume – B. Gas particles are in constant motion. – C. Collisions between gas particles are elastic. – D. There are no repulsive or attractive forces acting between gas particles. – E. Temperature is a measure of the average speed of gas particles.

Behavior of Gases Gases have low densities. Gases have lots of empty space between particles. Gases have no definite volume. They can be compressed or expanded. Gases diffuse evenly through out a space based upon their temperature and molar mass. Kinetic Energy = ½ m v 2 where: m = mass and v = velocity, speed

Graham’s Law of Effusion At the same temperature, two gases will effuse at a rate based upon their molar mass. The heavier the gas the slower it moves. The lighter the gas the faster it moves. See board for equation.

Gas Pressure Because gas has mass, it creates a pressure. Pressure = Force / Area The higher up in the atmosphere you go, the less air, the less air pressure. Air pressure is the weight of air over an object. Units used to measure pressure: Atmospheres, (Atm), Kilopascals, (KPa), millimeters of mercury, (mmHg)

Standard Pressure is pressure at sea-level at 0 o C. 1.0 atm = kPa = 760 mm Hg Dalton’s Law of Partial Pressures P total = P 1 + P 2 + P P n The total pressure in a closed container is equal to the sum of all pressures in the container.

Intermolecular Forces Intermolecular forces are forces that hold particles together. They are not the same as a chemical bond. Dispersion Forces – weak forces caused by the movement of electrons. Dipole Forces – attractive forces between polar molecules. Hydrogen Bonds – special type of dipole force between hydrogen and an unshared pair of electrons.

Properties of Liquids The kinetic molecular theory can also be applied to liquids and solids. Liquids are more dense than gases because the particles are closer together. Liquids are only slightly compressible. Liquids have no definite form so they can flow. Liquids are fluid. Liquids have a viscosity. Viscosity is a measurement of the resistance to flow.

Viscosity is temperature dependent. The higher the temperature, the more a liquid flows. Think pancake syrup. Cold syrup – pours slowly. Warm syrup – pours very quickly. Surface Tension – is a measurement of the inward pull by particles on the surface of a liquid. The more surface tension a liquid has, the more it will ball up. Think about water on a freshly waxed car. Raindrops are round because of this.

Properties of Solids Solids vibrate about fixed points. Solids tend to be the densest phase of matter for most substances. Two types of solids: Crystalline and Amorphous Crystalline solids have a definite arrangement of atoms. – Crystals come in definite shapes – Crystalline solids have definite melting points

Amorphous solids has no regular repeating pattern. Amorphous solids have no definite melting point. You can also classify solids by the type of bonds that they have. – Molecular solids – covalent bonds – Ionic solids – ionic bonds – Metallic solids – metallic bonds

Phase Changes All phase changes are reversible. All phase changes comes in pairs. – Freezing – Melting solids and liquids – Vaporization – Condensation liquids and gases – Sublimation – Deposition solids and gases All phase changes involve a change in energy. One is exothermic and one is endothermic. For a phase change to occur, particles must have some minimum kinetic energy.

Melting - Freezing Melting points and freezing points are always the same. When particles have enough energy to overcome Intermolecular forces, phase change happens. Temperature remains constant during phase change.

Vaporization / Evaporation Vaporization is the change of a liquid to a gas. Vaporization or Boiling take place at a specific point. Evaporation can take place at any temperature. Boiling points vary, but take place through out the whole liquid. Evaporation only happens at the surface of a liquid.

Evaporation Evaporation is a slow change from a liquid to a gas. Evaporation can be increased by several ways. – Increase the room temperature. – Increase air currents over liquid. – Increase surface area of liquid. Evaporation can even take place at temperatures below freezing.

Boiling Points For boiling to take place, particles have to have a certain amount of energy. Boiling point is also affected by atmospheric pressure. Normal boiling point is the boiling point at standard pressure. Water can boil at any temperature.

Sublimation / Deposition Sublimation is the direct change from the solid phase to the gaseous phase. Deposition is the opposite of sublimation. Some examples of sublimation: – Dry ice, frozen CO2 – Freezer burn

Phase Diagrams Phase diagrams show the phases of a substance at different temperatures and pressures. Each substances phase diagram is a little different.

The triple point is the exact temperature and pressure where all three phases exist at the same time. The critical point is where you can no longer change a gas back to a liquid.