Transcript Chapter 2 - Cloudfront.net

MATTER
AND
CHANGES
Chapter 2
Matter: An Introduction
• Matter has different properties that allow
us to distinguish different types of matter.
• Matter can undergo physical and/or
chemical changes.
• The components of compounds and
mixtures can be separated; elements
cannot.
• Chemical and physical changes occur with
a preservation of mass.
Remember Matter &
Chemistry?
Chemistry
The study of the composition of
matter and the changes that matter
undergoes.
Matter
Anything that has mass and
occupies space.
Describing Matter
Matter has mass and volume.
Extensive Properties: A property that


depends on the amount of matter in a
sample.

Size dependency.
Intensive Properties: A property that

depends upon the type of matter in a
sample, not the amount of matter.

Independent of size.
What is a substance?
Matter that has a uniform and
definite composition.
Every sample of a given substance has
identical intensive properties because
every sample has the same composition.
Substances can be elements like:
Sodium (Na)


Bromine (Br)
Mercury (Hg)
Elements are the simplest form of matter
that has a unique set of properties.
Elements are pure substances made up of
only one kind of atom.
Or substances can be compounds like:
Water

Rust
Compounds are substances that contain
two or more elements chemically
combined in a fixed proportion.
Compounds
NaHCO3 Baking Soda
sucrose
C12H22O11
Name these everyday
compounds from
their formula.
Can we break these
down?
H2O
water
Symbols and Formulas

Chemical symbols are used to represent
elements. Often elements are single
letters or two letters.
N = nitrogen, Na = sodium, etc.

Chemical formulas are used to
represent compounds. Formulas are
always multiple letters combined with
numbers.
H2O = water, C12H22O11 = sucrose, etc.
Identifying a Substance
Physical Change vs.
Chemical Change
Boiling of Water
Electrolysis of Water
How to ID a substance?
Answer #1: Use its physical properties.
A quality or condition of a substance that
can be observed or measured without
changing the substance’s composition.
Examples: Hardness, color, conductivity,
melting or boiling points, physical state at
room temperature & malleability.
Physical Properties of
Some Substances
Substance
State
Color
Melting Point
(oC)
Boiling Point
(oC)
Chlorine
Gas
Greenishyellow
-101
-34
Oxygen
Gas
Colorless
-218
-183
Ethanol
Liquid
Colorless
-117
78
Mercury
Liquid
Silvery-white
-39
357
Sulfur
Solid
Yellow
115
445
Copper
Solid
Reddish-yellow
1084
2562
States of
Matter
LIQUID
GAS
SOLID
Solids
A form of matter that has a
definite shape and form.
• Particles are packed tightly
together.
• Virtually incompressible.
• Only slightly expands with heat.
Liquids
A form of matter that has an
indefinite shape, flows, yet
has a fixed volume.
• Particles are not arranged rigidly
• Particles are in close contact with
each other.
• Free flowing
• Volume does not change as shape
of container changes;
volume is fixed.
• Almost incompressible
• Expands slightly when heated
Gas A form of matter that takes both the
shape and volume of its container.
• Great distances and
no interactions between
particles.
• Easily compressible
• Have indefinite shape and
volume
• Free flowing
Gas vs. Vapor
Gas: Term used for substances that exists in
the gaseous state at room temperature.
Vapor: Term used for the gaseous state
of a substance that is usually a
liquid or a solid at room
temperature.
Physical Changes
During the course of a physical
change the properties of a material
change, but the composition of the
material does not change.
• Physical changes can be reversible
or irreversible.
Reversible Changes
Irreversible Changes
• Boiling
• Break
• Freezing
• Split
• Melting
• Grind
• Condensation
• Cut
• Crush
Reversible changes involve a change
in the physical state.
How to ID a substance?
Answer #2: Induce a chemical change.
A change that produces matter with a
different composition than the original
matter.
Example: Decomposing water to hydrogen gas
and oxygen gas. Each product will have different
properties from the reactant.
Chemical Changes


During a chemical change the
composition of matter always changes.
The chemical properties of a substance
can be observed only when it
undergoes a chemical change.
Chemical Property: The ability of a substance
to undergo a specific chemical change.
Chemical Change = Chemical Reaction



Reactant: The substances present at the
start of the chemical reaction.
Product: The substances present at the
completion of the chemical
reaction.
The reactant is not the same as the
product.
Combustion of sugar
The reaction of zinc and hydrochloric acid
The reaction of iron with sulfur
Recognizing Chemical Changes
1.) Production of a gas.
2.) Transfer of energy.
3.) Formation of a precipitate or
a color change
Conservation of Mass


During a chemical reaction, the mass of
the products is always equal to the mass of
the reactants.
Law of Conservation of Mass: In any
physical or chemical change, mass is
conserved.
Mass Changes in Physical and
Chemical Changes

Mass in physical changes.



Weigh mass before and after change.
Mass before and after is always the same.
Mass in chemical changes.


Weigh reactants and products.
Mass of reactants and products should also
be the same, but not always. Why?
Mixtures
Mixtures are physical blends of two
or more components each of which
retains its own properties/identities.


Most samples of matter are mixtures.
Two categories of mixtures:
heterogeneous and homogeneous.
Heterogeneous Mixture

This is a mixture in which the
composition is not uniform throughout.
Homogeneous Mixture

This is a mixture that has uniform
composition throughout.
The Phases of the Mixtures
Phase: any part of a sample with
uniform composition and properties.
Vinegar
Homogeneous Mixtures =
one phase
Oil &
Vinegar
Heterogeneous Mixtures =
Two or more phases
Separating Mixtures



Use differences in physical properties to
separate the components of a mixture.
Filtration: Process that separates a solid
from a liquid (making coffee).
Distillation: Process that separates a liquid
from a liquid or liquids from solids
dissolved in them. (distilled water).
Examples of Distillation Devices
Examples of Filtration Devices
Distinguishing Substances
and Mixtures



Use the general characteristics of each to
distinguish a mixture from a substance. This is
the harder way to go.
Fixed composition = Substance
Varied composition = Mixture
We can physically separate mixtures into their
component parts. We cannot do so with
substances.
MATTER
AND
CHANGES
Chapter 2
The End