Chapter 12

1. SOLID 2. LIQUID 3. GAS 4. PLASMA

SolidsLiquidsGassesPlasmas Definite ShapeIndefinite Shape Definite Volume Indefinite Volume High DensitiesLower Densities than solids, but higher than gases. Extremely low densities Particles very ordered- vibrating, but not moving past each other. Particles associate with each other, but move freely past one another. Particles are very far apart and move freely without associating with other particles. Particles’ nuclei and electrons have disassociated from each other.

A plasma is a gas that has been energized to the point that some of the electrons break free from, but travel with, their nucleus. Gases can become plasmas in several ways, but all include pumping the gas with energy. Plasma can glow brightly and it responds to electric and magnetic fields.

Plasma is by far the most common form of matter. Plasma is 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.  A lightning strike is an example of plasma The Orion Nebula is an example of plasma Neon signs are also plasma

There are three things that contribute to the state of matter something is found at: Molecular Forces, Temperature, and Pressure. At a specific temperature and pressure, different substances are found in different states of matter due to their molecular forces. The stronger the intramolecular/intermolecular forces, the more energy is needed to separate the molecules.  Ionic and metallic compounds are normally solids at room temp  H-bonded and dipole-dipole compounds are normally liquids at room temp  Dispersion compounds are normally gases at room temp

A change of state, also called a phase change, is a physical change from one state of matter to another.  For example, from solid to liquid or from liquid to gas. How can this happen?  The answer lies in the motion of the atoms in matter. If a physical force such as temperature or pressure changes, the state can change.

Generic Heating/Cooling Curve Why is the temperature constant while a substance changes phases?

Freezing is the phase change as a substance changes from a liquid to a solid. Melting is the phase change as a substance changes from a solid to a liquid. Condensation is the phase change as a substance changes from a gas to a liquid. Vaporization is the phase change as a substance changes from a liquid to a gas.  Two types: Evaporation and Boiling Sublimation is the phase change as a substance changes from a solid to a gas without passing through the intermediate state of a liquid. Deposition is the phase change as a substance changes from a gas to a solid without passing through the intermediate state of a liquid.

If the container is closed, an equilibrium is reached where an equal number of molecules return to the surface. The pressure of this equilibrium is called the saturation vapor pressure. Evaporation is a surface phenomenon - some molecules have enough kinetic energy to escape.

Boiling occurs when many molecules throughout the system have enough kinetic energy to escape as a gas.

Changes in Temperature can change the state of matter. If energy, in the form of temperature, is added atoms move faster. Have enough energy to escape the forces holding them together (intermolecular forces and pressure) If energy (temperature) is taken away, particles move slower.

Temperature is not the only thing that effects the phase of matter. Pressure changes can also contribute to matter changing into different states.  An increase in pressure increases the energy needed to escape the state.  A decrease in pressure decreases the energy needed to escape the state. Temperature and Pressure have inverse affects on the state of matter.  This is depicted using a “phase diagram” which relates states of matter to differing temperatures AND pressures.

Generic Phase Diagram

Melting/Freezing Point - The temperature and pressure at which the liquid and solid state are at equilibrium. Boiling Point - The temperature at which the vapor pressure of a liquid is equal to the pressure on the liquid. NOTE:  The line between the solid and liquid phases is a curve of all the freezing/melting points of the substance.  The line between the liquid and gas phases is a curve of all the boiling points of the substance. TRIPLE POINT - The temperature and pressure at which the solid, liquid, and gas phases exist simultaneously. CRITICAL POINT - The temperature above which a substance will always be a gas regardless of the pressure.

melting freezing sublimation deposition vaporization condensation

Which state of matter tends to exist under:  High Temp, High Pressure  Liquid  High Temp, Low Pressure  Gas  Low Temp, High Pressure  Solid

What state of matter is water in at 50.0 degrees C and 1 atm?  Liquid What temp. & pressure is the critical point at for water?  C & atm **Refer to p. 429 if you can’t see the diagram