Phases of Matter

Solids Particles are tightly packed in an orderly pattern. Can’t move about. Can only shake or vibrate. Particles are tightly packed in an orderly pattern. Can’t move about. Can only shake or vibrate.

Gases Particles are far apart and can move rapidly from place to place. Particles are far apart and can move rapidly from place to place. Gases can move from place to place (translation), they can tumble (rotation), & they can shake (vibration). Gases can move from place to place (translation), they can tumble (rotation), & they can shake (vibration).

Liquids There is a little space between particles & they can slide past each other. Little or no order. There is a little space between particles & they can slide past each other. Little or no order. Liquids can vibrate & have very hindered translation and rotation – the particles can move a little bit but then they bump into a neighbor. Liquids can vibrate & have very hindered translation and rotation – the particles can move a little bit but then they bump into a neighbor.

Liquids Condensed phases = liquid & solid phases. Particles are close together.

Kinetic Energy Atoms & molecules are in constant motion. Atoms & molecules are in constant motion. Temperature is an assessment of the average K.E. of the particles in a sample of matter. Temperature is an assessment of the average K.E. of the particles in a sample of matter. If the temperature , the avg. K.E. If the temperature , the avg. K.E. If temperature , then avg. K.E. If temperature , then avg. K.E.  

Temperature vs. Motion A gas & a solid at the same temp have the same avg. K.E., but the particles in the 2 phases move very differently. A gas & a solid at the same temp have the same avg. K.E., but the particles in the 2 phases move very differently.

Why do liquids & solids exist? What holds them together?

Intermolecular Forces There are attractive forces between all particles of matter called intermolecular forces. There are attractive forces between all particles of matter called intermolecular forces. Intermolecular forces arise because atoms contain charged particles – protons & electrons. Intermolecular forces arise because atoms contain charged particles – protons & electrons. Not as strong as bonding within a molecule, but intermolecular forces are responsible for solids & liquids. Not as strong as bonding within a molecule, but intermolecular forces are responsible for solids & liquids.

Intermolecular Forces All molecules are attracted to each other. All molecules are attracted to each other. Some molecules are strongly attracted & some are only weakly attracted. Some molecules are strongly attracted & some are only weakly attracted. If it wasn’t for intermolecular forces, everything would be a gas!!! If it wasn’t for intermolecular forces, everything would be a gas!!!

What is a phase change? A transition between phases. There are 6. What are they? A transition between phases. There are 6. What are they?

source H 2 O(l)  H 2 O(g) Boiling or Vaporization

source H 2 O(s)  H 2 O(l) Melting or Fusion

source I 2 (s)  I 2 (g) Sublimation I 2 (g)  I 2 (s) Deposition

source H 2 O(g)  H 2 O(l) Condensation

source H 2 O(l)  H 2 O(s) Freezing

source Chunk of dry ice in water.

Phase Changes When a substance goes from the gas to a condensed phase, what happens? When a substance goes from the gas to a condensed phase, what happens? The particles get closer together and their translational motion (movement from point A to point B) slows down. The particles get closer together and their translational motion (movement from point A to point B) slows down. We cool it and/or compress it. We cool it and/or compress it.

Gas to Liquid

Phase Changes When a substance goes from a solid to a liquid or a gas, what happens? When a substance goes from a solid to a liquid or a gas, what happens? The particles move far apart and their translational motion increases. The particles move far apart and their translational motion increases. We heat them up and/or reduce the pressure. We heat them up and/or reduce the pressure.

Phase is determined by the competition between kinetic energy & intermolecular forces

Kinetic Energy vs. Intermolecular Forces

Kinetic Energy  Intermolecular Forces Weak intermolecular forces: even with low K.E. the particles can “escape” from one another & move far apart. Weak intermolecular forces: even with low K.E. the particles can “escape” from one another & move far apart. Move the magnets past each other quickly. Can the magnet in your right hand feel the magnet in your left hand? Move the magnets past each other quickly. Can the magnet in your right hand feel the magnet in your left hand? What phase has weak intermolecular forces? What phase has weak intermolecular forces? Gas phase

Intermolecular Forces  Kinetic Energy Strong intermolecular forces: the particles may be trapped next to each other unless they are moving fast. Strong intermolecular forces: the particles may be trapped next to each other unless they are moving fast. Move the magnets past each other slowly. What happens? Move the magnets past each other slowly. What happens? What phase has strong intermolecular forces? What phase has strong intermolecular forces? Solid phase

Solid Phase – strong intermolecular forces Solid Phase – strong intermolecular forces The stronger the intermolecular forces, the higher the melting point & boiling point. The stronger the intermolecular forces, the higher the melting point & boiling point. Gas Phase – weak intermolecular forces Gas Phase – weak intermolecular forces The weaker the intermolecular forces, the lower the melting point & boiling point. The weaker the intermolecular forces, the lower the melting point & boiling point.

Sublimation What can you say about the intermolecular forces in I 2 ? (I 2 sublimates.) What can you say about the intermolecular forces in I 2 ? (I 2 sublimates.) They are pretty weak! They are pretty weak!

Particle Diagram of I 2 White lines represent forces of attraction between I 2 molecules.

Potential Energy of a Pure Substance Equal quantities of ice & water at 0  C have the same kinetic energy, although the molecules move differently in the 2 phases. Equal quantities of ice & water at 0  C have the same kinetic energy, although the molecules move differently in the 2 phases. They have different potential energy. They have different potential energy. The farther apart the particles, the greater the potential energy. The farther apart the particles, the greater the potential energy. For potential energy, gases  liquids  solids. For potential energy, gases  liquids  solids.

Potential vs. Kinetic Energy of H 2 O How can I start with H 2 O at 0  C and raise the temperature to 50  C? How can I start with H 2 O at 0  C and raise the temperature to 50  C? I have to add energy to the system and it increases the kinetic energy of the water molecules. They move faster. I have to add energy to the system and it increases the kinetic energy of the water molecules. They move faster.

Potential vs. Kinetic Energy of H 2 O How can I start with ice at 0  C and convert it to water at 0  C? How can I start with ice at 0  C and convert it to water at 0  C? I have to add energy to the system and it increases the potential energy of the particles. They move father apart from one another. I have to add energy to the system and it increases the potential energy of the particles. They move father apart from one another.

Solid Liquid Gas Potential Energy of System Going Up the ladder = Endothermic Process Net gain in energy. Going Down the ladder = Exothermic Process Net loss in energy.

Solid Liquid Gas Potential Energy of System Going Up the ladder… Endothermic Process Endothermic Process (Net gain in energy ) Going Down the ladder… Exothermic Process Exothermic Process (Net loss in energy )

source

Temperature Time Q = mH f Q = mH v Q = mC l  T Q = mC s  T Q = mC g  T