States of Matter Unit 7

Overview States and Properties of Matter Kinetic Molecular Theory Phase Changes Diagrams Phase Diagrams Heating/Cooling Curves Heat of Fusion/Vaporization Vapor Pressure

States of Matter Based upon particle arrangement Based upon energy of particles Based upon distance between particles

3 States of Matter SOLIDS — have rigid shape, fixed volume; external shape can reflect the atomic and molecular arrangement Reasonably well understood LIQUIDS — have no fixed shape and may not fill a container completely Not well understood GASES — expand to fill their container Good theoretical understanding

Solids Definite shape & definite volume Not easily compressible Particles of solids are tightly packed, vibrating about a fixed position. Not easily compressible Little free space between particles Do not flow easily Particles cannot move/slide past one another Infinite number of free surfaces

Solids (Types) Crystalline Solids: highly regular arrangement of their components Amorphous solids: considerable disorder in their structures (glass, plastic).

Allotropes Some chemical elements can exist in two or more different forms. Atoms of the element bond together differently. Diamond, carbon atoms bond together in a tetrahedral lattice Graphite, carbon atoms bond together in sheets

Liquids Indefinite shape but definite volume Not easily compressible Particles are tightly packed, but are far enough apart to slide over one another. Not easily compressible Little free space between particles Liquids flow easily Particles can move/slide past one another Have one free surface

Surface Tension Intermolecular cohesive attraction causing liquid to minimize its surface area Mostly in polar molecules and liquid metals

Illustration of capillary action for large and small bore capillaries. Attraction of the surface of a liquid to the surface of a solid, which causes the liquid to rise in a tube Illustration of capillary action for large and small bore capillaries.

Glycerine, also called glycerol, is a liquid with a high viscosity Liquids are fluids – they FLOW. Viscosity is the resistance to flow. Example: Syrup has a higher viscosity than water. Glycerine, also called glycerol, is a liquid with a high viscosity High viscosity = strong intermolecular forces

Viscosity decreases as temperature increases.

Gases Indefinite shape and indefinite volume Easily compressible Particles are very far apart and move freely Easily compressible There is a great deal of free space between particles Flow very easily Particles randomly move past one another Gases have no free surfaces

Plasma 1879 - Sir William Crookes, an English physicist, identified a fourth state of matter, now called plasma Plasma is by far the most common form of matter Plasma in the stars and in the tenuous space between them makes up over 99% of the visible universe and perhaps most of that which is not visible

Plasma An ionized gas Very good conductor of electricity Composed of ions Affected by magnetic fields Indefinite shape and indefinite volume Particles can move past one another. Easily compressible Great deal of free space between particles.

Computer chips and integrated circuits Computer hard drives Products manufactured using plasmas impact our daily lives: Computer chips and integrated circuits Computer hard drives Electronics Machine tools Medical implants and prosthetics Audio and video tapes Aircraft and automobile engine parts Printing on plastic food containers Energy-efficient window coatings High-efficiency window coatings Safe drinking water Voice and data communications components Anti-scratch and anti-glare coatings on eyeglasses and other optics

Kinetic Molecular Theory 1. pertaining to motion. 2. caused by motion. 3. characterized by movement: Running and dancing are kinetic activities. Origin: 1850–55; < Gk kīnētikós moving, equiv. to kīnē- (verbid s. of kīneîn to move) + -tikos Source: Websters Dictionary

Kinetic Molecular Theory Atoms and molecules are constantly in motion. SOLIDS — little movement between particles LIQUIDS — more space between them than a solid does, but less than a gas GASES — molecules are moving in random patterns with varying amounts of distance between the particles

Changes of State Changing states requires a change in the energy of a system. Changing states may also be due to the change in pressure in a system.

Changes of State

Phase Diagrams

Phase Diagrams (T) Triple Point: temperature and pressure at which all three phases exist simultaneously in equilibrium (C) Critical Point: temperature and pressure beyond which the liquid and solid phase is distinguishable (supercritical liquid) molecules of a substance have too much kinetic energy to stick together (page 453 of book = supercritical fluid)

Phase Diagrams

Water

Carbon dioxide

Carbon

Heat of Fusion (formation) Energy that must be put into a solid to melt it Needed to overcome forces holding it together Heat of fusion given off when liquid freezes Intermolecular forces within solid more stable and have lower energy than forces within liquid so energy is released during freezing

Heat of Vaporization Energy that must be put into a liquid to turn it into a gas Energy needed to overcome forces holding liquid together Heat of vaporization given off when gas condenses Intermolecular forces become stronger when gas condenses so as gas becomes liquid (more stable), energy is released Heat of vaporization larger than heat of fusion Many more intermolecular forces must be overcome in vaporization than melting (intermolecular forces severed in vaporization but many carry over between solids and liquids)

Heating/Cooling Curves As heat added to a substance in equilibrium, temperature of substance can increase or the substance can change phases, but both changes cannot occur simultaneously Horizontal line at melting point is heat of fusion Horizontal line at boiling point is heat of vaporization

Heating/Cooling Curves

Vapor Pressure The pressure exerted by molecules as they escape the surface of a liquid and become a gas As temperature increases, vapor pressure of a liquid increases When vapor pressure of liquid increases to point where equal with the surrounding atmospheric pressure, the liquid boils The weaker the intermolecular forces, the easier it is for molecules to escape the surface and turn to gas Weaker intermolecular forces = higher vapor pressure

Vapor Pressure - Equilibrium As number of gas molecules increases, higher probability that gas molecule will hit surface of liquid and be recaptured When there is even exchange of liquid and gas molecules, vapor pressure becomes constant (dynamic equilibrium) Appears that nothing is happening in the system Vapor pressure of a liquid is the pressure exerted by its vapor when the liquid and vapor states are in equilibrium When liquid/solid phase is in equilibrium with the gas phase, the pressure of the gas equals the vapor pressure of the substance