Liquids and Solids Chapter 12

Properties of Liquids and the KMT Liquid- can be described as a form of matter that had definite volume and takes the shape of its container Fluid- A substance that can flow and therefore takes the shape of its container

6 properties of liquids Relatively high density- this is a result of the close arrangement of particles Relative incompressibility- liquids are much less compressible than gases because the particles are more closely packed together Ability to diffuse- occurs because of the constant random motion of particles

Surface tension- a force that tends to pull adjacent parts of a liquid’s surface together Capillary Action- the attraction of the surface of a liquid to the surface of a solid (root pressure in plants) Evaporation- a process by which particles escape and enter the gas phase from a non boiling liquid.

Vaporization – is the process by which a liquid or solid changes into a gas. Evaporation is a form of vaporization. 2 examples - perfume & fresh water from oceans

Introduction to Solids When a liquid is cooled, the average energy of its particles decreases The physical change of a liquid to a solid by removal of heat is called freezing (solidification) All liquids freeze…but not necessarily at temperatures you normally encounter.

Formation of Solids Properties of solids and the KMT Definite shape and volume-particles are packed closely together compared to liquids and gases. Definite melting point- the temperature at which a solid becomes a liquid High density and low compressibility Low rate of diffusion

2 Types of Solids Crystalline solids- consists of crystals in which the particles are arranged in an orderly, geometric, repeating pattern Amorphous solids -amorphous means “without shape” -fiberglass, optical fibers, some plastics and glass are amorphous solids

Concept Questions Describe the liquid state according to the KMT. List the properties of liquids. Why do liquids in a test tube form a meniscus? Compare vaporization and evaporation.

Concept Questions Describe the solid state according to the KMT. What is the difference between amorphous solid and a crystalline solid? Why do solids have definite volume, high density and extremely low rates of diffusion?

Changes of State Section 12.3

6 phase changes Solid  liquid melting Solid  gas sublimation Liquid  solid freezing Liquid  gas vaporization Gas  liquid condensation Gas  solid deposition

Equilibrium- a dynamic condition in which 2 opposing changes occur at equal rates in a closed system Phase- any part of a system that has uniform composition and properties

An equilibrium equation Liquid + heat energy  vapor Vaporization/evaporation Vapor  liquid + heat energy Condensation Liquid + heat energy  vapor Liquid-vapor equilibrium

What state of matter is (a)? What about (b)? _________________ is occurring at (c)?

Le Chatelier’s Principle A system will remain at equilibrium until something occurs to change this condition Le Chatelier’s principle- when a system is disturbed by application of a stress, it attains a new equilibrium position that minimizes stress Stress- any change in concentration, pressure, or temperature

Let’s look again at our equilibrium system… Liquid + heat energy  vapor Which direction is the endothermic reaction? Which direction is the exothermic direction?

Equilibrium Shifts CHANGE SHIFT Adding liquid Removing liquid Adding vapor Removing vapor Decrease volume Increase volume Decrease temperature Increase temperature

Volatile and Nonvolatile Liquids Volatile liquids- liquids that evaporate readily Nonvolatile liquids- evaporate slowly, have strong attractive forces between particles

Boiling Boiling point-conversion of a liquid to a vapor within the liquid as well as at its surface.

Freezing and Melting Freezing point- the temperature at which the solid and liquid are in equilibrium at 1 atm pressure

Stop

Phase Diagrams Phase diagrams- a graph of pressure versus temperature that shows the conditions under which the phases of a substance exist Triple point- indicates the temperature and pressure conditions at which the solid, liquid, and vapor of the substance can coexist at equilibrium

Critical temperature- the temperature above which the substance cannot exist in the liquid state Water 373.99°C Critical pressure- the lowest pressure at which the substance can exist as a liquid at the critical temperature Water 217.75 atm

At 6 atm, what is the boiling point of carbon dioxide?

Stop

Water Water is the Earth’s most abundant liquid Oceans, rivers, and lakes cover about 75% of the earth’s surface 70-90% of the mass of living things is water

Structure of Water The molecules in solid or liquid water are linked by hydrogen bonding Ice consists of water molecules in a hexagonal arrangement. The empty spaces between molecules in this pattern accounts for the low density of ice Once the molecule is heated, water molecules can crowd closer together Thus, liquid water is denser than ice.

Physical Properties of Water Pure liquid water is transparent, odorless, tasteless, and almost colorless Any observable impurities are caused by dissolved minerals, liquids, or gases It has a unique property of expanding in volume when it freezes This explains why ice floats in water.

Molar heat of vaporization It is a measure of the attraction between the particles of a liquid Molar heat of fusion (H)- Depends on the attraction between the solid particles

Calculating Molar Heat q = m (H) q = heat (J) m = mass (g) Hvaporization H2O = 2260 J/g Hfusion H2O = 334 J/g

Practice Problems How much heat energy is absorbed when 47.0 g of ice melts at STP? How much heat energy is absorbed when this same mass of liquid water boils? What quantity of heat energy is released when 506 g of liquid water freezes? What mass of steam is required to release 4.97 x 105 kJ of heat energy on condensation?