• What Is Chemistry and Why Is It Important?

Reactions are the processes of change matter undergoes, and includes the energy changes that accompany these processes.

Matter
Anything that takes up space and has mass

Mass
The quantity of matter in any given object

Chemical
Any substance with a definite composition

Any solid, liquid or gas used in or produced by a chemical process, either man-made or natural contains chemicals.

Chemicals—solids, liquids, or gases found in and on the Earth, the crust of the Earth, the oceans and the atmosphere, living organisms, comets, asteroids and the other planets of the solar system.

Things made of chemicals:
Air, gasoline, a dead leaf, a Snickers Bar, steel, wood, shampoo, poop, urine, water, oxygen, gold, beer, etc.

• Chemistry helps us understand our world:

Because living and nonliving things are made of matter and matter is composed of chemicals, chemistry affects all aspects of life and most natural processes.

• What Are Physical Properties?

Physical properties can be classified as either extensive or intensive.

Extensive Properties
physical properties that depend on the amount of matter in a sample

Mass and volume are extensive properties.
 

Mass the amount of matter an object contains

Volume  the amount of space an object occupies

Intensive Properties
physical properties that depend on the type of matter in the sample, not the amount

Examples:

Melting Point Boiling Point State at 20 ºC (solid, liquid, gas) Color Luster (shine) Odor

Hardness Malleability (can be molded into a shape) Ductility (can be drawn into a wire) Conductivity (of both heat and electricity) Density

• Every pure substance has a unique set of intensive physical properties.

• Every sample of a given substance has identical intensive properties because they all have the same composition

• In what physical states does matter exist?

Solids
Definite shape and volume
Low-energy particles packed closely in a rigid arrangement
Not easily compressed
Tend to expand only slightly when heated

     Example of a Solid: iron

Liquids
Definite volume but indefinite shape
—takes the shape of its container
Mid-energy particles are close together, but free to flow around one another
Not easily compressed
Tend to expand only slightly when heated

     Example of a Liquid: alcohol

Gases
Indefinite shape and volume
—takes the shape and fills the volume of its container
High-energy particles are relatively far apart and move freely with little interaction
Easily compressed
Expand when heated

     Example of a Gas: carbon dioxide

Vapor
The gaseous state of a substance that is usually liquid or solid at room temperature

Example:
Water vapor

Water is usually solid at room temperature, so when it is in a gaseous state, water is referred to as a vapor.

Matter can also be transformed into a form called plasma:
 

Plasma A form of matter in which the negatively charged particles of an atom, the electrons, have been stripped away from the positively charged nuclei.

Is plasma a chemical?

• Unlike the three states of matter—solid, liquid, and gas—plasma is not composed of chemicals.

In what physical states does matter exist?
 

Practice Problems Answer the following questions:

9. What are the three states of matter?

10. Which states of matter are being described? . a)  Volume does not change in a different container . b)  Has a very low density . c)  Has large distances between particles . d)  Shape depends on container . e)  Particles have a fixed arrangement

11. Which states of matter are being described? . a)  Which state has a definite volume but takes the shape of its container? . b)  Which state takes on the volume and shape of its container? . c)  Which state has a definite volume and shape?

12. Which is the technical difference between a gas and a vapor?

Change

Physical Changes
Changes affecting the form or appearance of a substance, not its composition

• Physical Changes can be classified as reversible or irreversible.

Examples:
boiling, melting, freezing, condensation

Changes in the form of a solid are irreversible.

Examples:
breaking, splitting, cutting, grinding, crushing, cracking

• How can matter be changed from one form to another?

Changes of State are reversible.

Example:
Freeze or boil water, or freeze it and then smash it into a million pieces—it will still be water.

Melting Point & Freezing Point
going from solid to liquid or liquid to solid

melting point
melting—changing from a solid to a liquid

solid is heated
particles begin moving faster
until they gain sufficient energy
overcome attractive forces holding them together

The melting point of something is also the temp at which it freezes.
 

freezing point
freezing—changing from a liquid to a solid

temperature of liquid is lowered
energy in the particles of the liquid is lost
particles move slower
attractive forces pull particles close together

Sublimation & Deposition
going from solid to gas or gas to solid without going through a liquid state

Sublimation
particles on surface of solid absorb enough heat to change directly to gas with no temperature change and without going through the liquid state

Example:
Dry ice, frozen CO2, sublimes at -78°C.
CO2 does not form a liquid.

Deposition
when gas changes directly to solid

Example:
Frost on windows in sub-freezing air

Evaporation
high energy particles at the surface of a liquid changing to gas, leaving the remaining liquid cooler overall

• When heat is removed, a reverse process takes place.

Boiling Point
the temperature at which a liquid changes to gas (boils) and gas changes to liquid (condenses)

Boiling
the formation of gas bubbles from the liquid

Heating and Cooling Curves

What is the difference between reversible and irreversible changes of state?
 

Practice Problems Answer the following questions:

13. What is a physical change?

14. What is the difference between a reversible and an irreversible change? Give an example of each.

15. What is a change of state?

16. List and define seven changes of state.

17. What are the two phase changes that “skip over” one of the states?

18. How do you know when something is boiling?

19. Using a cooling curve for water, identify the state or change of state for water as solid, liquid, gas, condensation or freezing. . a)  at 120 °C b)  at 100 °C c)  at 40 °C . d)  at 0 °C e)  at –10 °C