Modern Chemistry Chapter 10

States of Matter

Kinetic-Molecular Theory

• The kinetic-molecular theory of matter is based on the idea that particles of matter are always in motion and this motion has consequences that affect its physical properties.

Kinetic-Molecular Theory of Gases

• 1- Gases consist of large numbers of tiny particles that are far apart relative to their size.

• 2- Collisions between gas particles and between particles and their container walls are elastic. An elastic collision is one in which there is no net loss of total kinetic energy.

• 3- Gas particles are in continuous, rapid, random motion. They therefore possess kinetic energy (energy in motion).

• 4- There are no forces of attraction between gas particles.

• 5- The temperature of a gas depends upon the average kinetic energy of the particles of the gas.

Gases have indefinite shape and indefinite volume.

The Kinetic-Molecular Theory and the Nature of Gases

• EXPANSION- Gases do not have definite shape or volume. They expand to completely fill any container.

• FLUIDITY- Gases flow so they are fluids.

• LOW DENSITY- The density of a gas is about 1/1000 that of the same substance in the liquid state.

• COMPRESSIBILITY- Gases can be compressed (the volume decreases) by applying pressure to the gas.

• DIFFUSION- Gases have the ability to spread and mix with one another due to the random motion of their particles.

• EFFUSION- A process by which gas particles under pressure pass through a tiny opening from one container to another.

Section 2- LIQUIDS

• A LIQUID is a substance that has definite volume but indefinite shape (it takes the shape of its container).

• Liquids are fluids because they have the ability to flow from one container to another and take the shape of the new container.

Properties of Liquids• 1- Liquids have a high density relative to gases. Their

density is about 1000 x that of the gas of the same substance.

• 2- Liquids are relatively not compressible.

• 3- Liquids have the ability to diffuse.

• 4- Liquids exhibit surface tension, a force that tends to pull adjacent parts of a liquid’s surface together, thereby decreasing the surface area to its smallest possible size. Surface tension resists penetration of objects into a liquid.

• 5- Liquids have capillary action, the attraction of the surface of a liquid to the surface of a solid.

Changes of Physical State• vaporization is the process by which

a boiling liquid changes to a gas

• evaporation is the process by which particles escape from the surface of a non-boiling liquid and enter the gas state

• boiling is the change of a liquid to bubbles of vapor that appear throughout the liquid

• freezing (solidification) is the physical change of a liquid to a solid by the removal of heat energy

Section 3SOLIDS

• solids have a definite shape and a definite volume

• crystalline solids consist of crystals, a substance in which the particles are arranged in an orderly, geometric, repeating pattern

• amorphous solids consist of particles that are randomly arranged

Properties of Solids1- DEFINITE SHAPE & VOLUME2- DEFINITE MELTING POINT

melting is the physical change from a solid to a liquid by the addition of heat

melting point is the temperature at which a solid becomes a liquid

supercooled liquid is a substance that retains certain properties of a liquid even at temperatures where it appears to be a solid (glass, plastics,…)

3- HIGH DENSITY (10x a liquid & 10,000x a gas)4- INCOMPRESSIBILITY5- LOW RATE OF DIFFUSION

Crystalline Solids

crystal structure is the total three-dimensional arrangement of particles of a crystal

crystal lattice is the representation of the arrangement of a crystal using a coordinate system

unit cell is the smallest portion of a crystal lattice that shows the three-dimensional pattern of the entire lattice

Types of Crystals

1) ionic crystals consist of positive & negative ions arranged in a regular pattern such as NaCl (salt) crystals

2) covalent network crystals consists of atoms covalently bonded to their adjacent atoms such as diamonds & SiO2 (sand)

3) metallic crystals consists of metal cations surrounded by delocalized valence electrons

4) covalent molecular crystals consists of covalently bonded molecules held together by intermolecular forces

Amorphous Solids

• Glass is made by cooling molten materials in a way that prevents them from crystallizing. This allows the glass to appear to be a solid yet be transparent.

• Other examples include plastics and semiconductors (used in electronics).

Section 4- Changes of State

1- The three most recognized physical states of matter are solid, liquid, & gas.

2- A phase is any part of a system that has uniform composition and properties.

3- When a substance changes its physical state is called a phase change.

• Condensation is the process by which a gas changes to a liquid.

• Equilibrium is a condition in which two opposing changes occur at equal rates (eg. liquid to gas = gas to liquid)

• Equilibrium vapor pressure is the pressure exerted by a vapor in equilibrium with its corresponding liquid at a given temperature.

• Volatile liquids are liquids that evaporate easily.

Boiling• Boiling is the conversion of a liquid to a vapor (gas)

throughout all parts of the liquid.

• Boiling point of a liquid is the temperature at which the equilibrium vapor pressure of the liquid equals the atmospheric pressure.

• Energy must be added continuously in order to keep a liquid boiling.

• Molar enthalpy of vaporization ( ΔHv ) is the amount of energy needed to vaporize one mole of a liquid at the liquid’s boiling point under constant pressure.

• Heat of vaporization is the amount of heat needed to vaporize one gram of a liquid at its boiling temperature.

• Heat of vaporization for water is 540 calories/gram.

Freezing & Melting

• Freezing is the physical change of a liquid becoming a solid. Also called solidification or fusion.

• Freezing point is the temperature at which a liquid becomes a solid and the solid and the liquid are at equilibrium.

• Molar enthalpy of fusion ( ΔHf ) is the amount of energy required to melt one mole of a solid at its melting point.

• Heat of fusion is the amount of heat needed to melt one gram of a solid.

• For ice, this is 80 calories/gram.

Other Changes of Physical State• Sublimation is the process by

which a solid changes to a gas, bypassing the liquid state.

• Examples include dry ice, moth balls, iodine, and ice at temperatures below 0°C.

• Deposition is the process by which a gas changes directly to a solid, bypassing the liquid state.

• An example would be frost.

Phase Diagrams• A phase diagram is a graph of pressure versus temperature that shows the

conditions under which the phases of a substance exist.

• The triple point of a substance indicates the temperature and the pressure conditions at which the solid, liquid, and vapor of the substance can coexist at equilibrium.

• The critical point of a substance indicates the critical temperature and pressure

• The critical temperature is the temperature above which a substance cannot exist in the liquid state.

• The critical pressure is the lowest pressure at which a substance can exist as a liquid at the critical temperature.

• Please see figure 16 on page 347 of the textbook.

• Use figure 16 to answer section review question #7 on page 348 of the textbook.

Section 5- Water• Hydrogen bonding in water molecules make water a unique

substance. Without hydrogen bonding, water would be a gas at room temperature.

• Hydrogen bonding allows water to form crystals when it freezes.

• Due to the crystal structure of ice, it is less dense than liquid water and will float.

• Floating ice acts as insulation to water below.

• If ice sank rather than floated, water would turn to solid ice in temperate climates and most of the living organisms in the water would die. Can you say frozen fish sticks?

Water

• Water freezes at 0°C and boils at 100°C.

• The molar enthalpy of fusion for water is 6.009 kJ/mol at one atmosphere of pressure.

• The molar enthalpy of vaporization for water is 40.79 kJ/mol at one atmosphere of pressure.

• Do practice problems #1 & #2 on page 351.

Questions about water.1. Why are there more orchards, vineyards, and vegetable farms

near Lake Erie than in central Ohio?

2. Why does steam cause more severe burns than boiling water?

3. Why do we use ice cubes?

4. Why does snow at very low temperatures (dry snow) contain less water than snow that falls at temperatures around freezing (wet snow)?

5. Why do we say that it takes about 7” of snow to equal 1” of water?

6. What causes the frost on car windows?

Chapter 10 Test Review

• 25 multiple choice questions– definition & applications of the kinetic-molecular theory– why matter changes phase– definition of temperature– examples of gas diffusion & gas effusion– expansion & compression of gases– effects of intermolecular forces and their application to states of matter– compare density & the states of matter– definitions of vaporization, evaporation, & sublimation– motion of the particles of a sample of matter in the three physical states– properties of solids, liquids, & gases– compare crystalline vs. amorphous solids– definitions of crystal types & crystal lattice– definitions of triple point, volatile– factors that affect boiling– the boiling process– the density of ice versus water– temperature of greatest density of water

Honors Chemistry Chapter 10 Test• 30 multiple choice questions

– definition & applications of the kinetic-molecular theory– why matter changes phase– definition of temperature– examples of gas diffusion & gas effusion– expansion & compression of gases– effects of intermolecular forces and their application to states of matter– compare density & the states of matter– compare the energies of the phases of matter– definitions of vaporization, evaporation, & sublimation– motion of the particles of a sample of matter in the three physical states– properties of solids, liquids, & gases– compare crystalline vs. amorphous solids– definitions of crystal types & crystal lattice– definitions of triple point, volatile– factors that affect boiling– the boiling process– the density of ice versus water– temperature of greatest density of water– two calculations using molar enthalpies