Matter and Change

Chemistry

Chapter 1

Try to Answer the Following Questions

1. A compound is formed by…a. A single elementb. Two or more atomsc. Two or more nucleid. Electrons and neutrons

2. Which statement best describes atoms and molecules in a liquid?

a. They vibrate rapidlyb. They form a definite structurec. They slide past each otherd. They cannot be rearranged

3. What is the process of a liquid changing to a gas called?4. Ice melting into water is a physical or chemical change?5. Which state of matter has neither a definite shape nor definite

volume?

How did you do?

1. “B”: two or more atoms

2. “C”: atoms and molecules in a liquid slide past each other

3. Evaporation

4. Physical

5. Gas

Introduction

What is chemistry?– The study of the composition of substances and the

changes (both physical and chemical) they undergo

What lead to the development of chemistry?– Alchemy

What other sciences does chemistry contribute to?– Biology– Geology– Physics

What does a Chemist do?

Develop new products (meds., cosmetics) Find methods to reduce pollution/clean up

environment Teaching Analyzing substances Quality of manufactured products Applied Chemistry: using knowledge to attain

specific goals (a.k.a. chemical technology)– Knowledge can be used to help or hurt

people/environment

Branches

Organic Chemistry– The study of all substances that come from carbon

Inorganic Chemistry– The study of all substances without carbon

Analytical Chemistry– The study of the composition of substances

Physical Chemistry– Theories and experiments that describe the behavior of

chemistry Biochemistry

– The study of chemistry of living organisms

Hypothesis vs. Theory vs. Scientific Law

A HYPOTHESIS is a proposed reason for what is observed and it needs to be tested by means of an experiment

A THEORY is a thoroughly tested explanation of why experiments give certain results.

A theory tends to explain WHY things happen. You cannot prove a theory.

Scientific Law is a concise statement that summarizes the results of a broad spectrum of observations and experiments.

Scientific Law tends to explain WHAT things happen. You can prove a scientific law.

Why does it “matter”?

What is matter?– “Everything that takes up space and has

mass”– “Stuff”

What is mass?Amount of matter an object contains

“How much stuff an object has”

**This is NOT the same as weight

Substances vs Mixtures

Matter is broken into categories. Matter can be either a substance or a mixture.

A substance is a particular kind of matter that has a uniform composition. This means that no matter the sample it will always have the same physical properties.– Eg. Elements and compounds– Other examples are: salt (NaCl), Fe,

Ag, Pb, water– What about lemonade?

Mixtures

A mixture is a physical blend of two or more substances. It has a variable composition and can be made of different ratios of substances.

Mixtures are ALWAYS physical changes

Types of mixtures

1. Heterogeneous mixtures-not uniform in composition

-more than one phase (a phase is a part of a system that is uniform in composition and physical state)

-examples: tossed salad, gravel mix, rock, river water

2. Homogeneous mixtures

-uniform in composition

-also called a solution

-easily confused with substances

-examples: salt water

A good question to ask yourself when trying to decide if something is a substance or a homogeneous mixture is to ask yourself if there is more than one kind of this material.

What is gasoline? What is milk? Are there different concentrations of salt?

Separating a Mixture

There are several ways to separate a mixture. A good way to figure out if matter is a substance or a solution is to see if you can separate it into parts by doing one of the following:

1. Physical separation2. Filter (particle size, uses gravity)3. Magnet (magnetism)4. Decanting-pouring off a liquid (density)5. Distillation (boiling point)6. Centrifuging (density)7. Chromatography (separates based on solubility)8. Crystallization

Lab: Classifying Matter

At each station, record answers to the following:

1) Identify the category of matter:a. Is it a pure substance? If so then is it an element or is it a compound?b. Is it a mixture? If so, then is it a heterogeneous mixture or homogeneous mixture?c. Write down the criteria you use for your categorization schemes.

2) Devise a separation strategy for any mixtures found. In other words, if you think you’ve spotted a mixture, how would you separate it into different components, and (if possible) all the way to the pure substances that comprise the mixture? (Remember, pure substances cannot be separated by physical means. They must be separated chemically, or, in the case of elements, by splitting atoms! That’s beyond the scope of the activity for the day.)  

Physical Properties

Matter contains both physical and chemical properties.

A physical property is a quality or condition of a substance that can be measured or observed without changing the substance’s composition.

Examples: Color, mass, density, hardness, odor, boiling point, solubility

Chemical Properties

Chemical properties are a little more difficult to determine. A chemical property is the ability of a substance to undergo chemical reactions

IE:Rot, rust, decompose, decay, grow ferment

You know that a chemical change has taken place because of a substance’s chemical properties.

Chemical vs. Physical Changes

Chemical Change– A change in the composition of a substance OR– Changing a substance to form a new substance– Examples: fermenting, rotting, burning, color change,

gas given off

Physical Change– A change in a substance without a change in its

composition– Examples: mixing, cutting, changing from a solid to a

liquid

Physical Property

Something that can be observed without altering the chemical state

Example: color, boiling point

Physical Change

A change that occurs without forming a new substance

Example: melting

DOES NOT FORM OR BREAK BONDS!

Chemical Property

Property of a substance related to a chemical change undergone by the substance

Example: metal dulls in air

Chemical Change

A reaction occurs and one or more new substances are formed

Example: Rusty cars

Figure it out- Chemical or Physical?

Metals are shiny Argon is put in light bulbs because it doesn’t

react Milk gets sour when left out Metals can be made into wires Bread rises when cooked Nonmetals are not able to conduct electricity

What is the basic difference between a chemical and a physical change? – After a physical change, it is still the same

substance (composition).

-After a chemical change, you have a NEW substance

States of Matter

There are four states of matter: solid, liquid, gas Solid -definite shape, definite volume Liquid -indefinite shape, definite volume Gas -indefinite shape, indefinite volume Plasma –gas like

What is compressibility?

Ability to squash something into a smaller volume

Solid, Liquid, Gas

(a) Particles in solid (b) Particles in liquid (c) Particles in gas

Gas, Liquid, and Solid

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 441

Gas Liquid Solid

Some Properties of Solids, Liquids, and GasesProperty Solid Liquid Gas

Shape Has definite shape Takes the shape of Takes the shape the container of its container

Volume Has a definite volume Has a definite volume Fills the volume of the container

Arrangement of Fixed, very close Random, close Random, far apartParticles

Interactions between Very strong Strong Essentially noneparticles

Solid

H2O(s) Ice

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 31

Ice

H2O(s) Ice

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 31

Photograph of ice model Photograph of snowflakes

Liquid

H2O(l) Water

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 31

In a liquid

• molecules are in constant motion

• there are appreciable intermolecular forces

• molecules are close together

• Liquids are almost incompressible

• Liquids do not fill the container

Liquids

The two key properties we need to describe areEVAPORATIONEVAPORATION and its opposite CONDENSATIONCONDENSATION

add energy and break intermolecular bonds

EVAPORATION

release energy and form intermolecular bonds

CONDENSATION

Gas

H2O(g) Steam

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 31

States of Matter

To evaporate, molecules must have sufficient energy to break IM forces.

Molecules at the surface break away and become gas.

Only those with enough KE escape. Breaking IM forces requires energy. The process

of evaporation is endothermicendothermic. Evaporation is a cooling process. It requires heat.

Evaporation

Change from gas to liquid

Achieves a dynamic equilibrium with vaporization in a closed system.

What is a closed system?

A closed system means matter

can’t go in or out. (put a cork in it)

What the heck is a “dynamic equilibrium?”

Condensation

When first sealed, the molecules gradually escape the surface of the liquid.

As the molecules build up above the liquid - some condense back to a liquid.

The rate at which the molecules evaporate and condense are equal.

Dynamic Equilibrium

As time goes by the rate of vaporization remains constant but the rate of condensation increases because there are more molecules to condense.

Equilibrium is reached when:

Rate of Vaporization = Rate of Condensation

Molecules are constantly changing phase “dynamic”

`The total amount of liquid and vapor remains constant “equilibrium”

Dynamic Equilibrium

• Vaporization is an endothermic process - it requires heat.

• Energy is required to overcome intermolecular forces

• Responsible for cool earth• Why we sweat

Vaporization

Energy Changes Accompanying Phase Changes

Solid

Liquid

Gas

Melting Freezing

Deposition

CondensationVaporization

Sublimation

Ene

rgy

of s

yste

m

Brown, LeMay, Bursten, Chemistry 2000, page 405