Download Chemical Change

NOTES: Introduction to
Chemistry
CHEMISTRY!
● CHEMISTRY = the study of the
composition of matter, its chemical and
physical changes, and the energy
changes that accompany these
changes.
The Nature of Science
● Scientific law versus theory:
-Scientific law: a summary of an
observed natural event
-Scientific theory: a well-tested
explanation of a natural event; supported
by EVIDENCE
The Way Science Works…
● Science involves critical thinking, or applying logic
and reason to observations and conclusions.
● Observation vs. Inference
-Observation: description of what you see, hear,
taste, feel, smell
-Inference: the conclusion you draw as a result of an
observation (not always correct!!)
Variables and Controls
● A variable is anything that can change in an
experiment.
-Independent variable: The variable being
changed or controlled by the scientist.
-Dependent variable: The variable being
measured or observed by the scientist.
● A controlled experiment tests only one variable at
a time.
The Scientific Method:
A series of logical steps to follow in order to
solve problems.
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OBSERVE
FORMULATE A QUESTION
FORM A HYPOTHESIS
DESIGN AND CONDUCT AN EXPERIMENT
MAKE OBSERVATIONS
RECORD AND ANALYZE DATA
DRAW CONCLUSIONS
FORMULATE NEW QUESTIONS and
CONTINUE CYCLE
Making Measurements
● Measurements are made in this class using SI
units.
● LENGTH (m): distance between 2 points
● VOLUME (L): space occupied
● MASS (g): the amount of matter in an object
● WEIGHT (N): the force with which gravity pulls on a
quantity of matter
Organizing Data
Data is organized and presented in tables, charts, and graphs.
Graph - visual representation of data
1) title
2) x and y axis labeled
3) units for both the x and y axis
4) scale is evenly and correctly spaced for data
5) legend when appropriate
Temperature Increase of a Beaker of Water
Temperature (K)
450
400
350
300
250
0
50
100
150
200
250
300
Time (sec)
LINE GRAPH: best for displaying data that change.
**a.k.a. a SCATTER PLOT!!
– Independent Variable: x-axis
– Dependent variable: y-axis
350
400
Number of Death's per 100,000
People
Leading Causes of Death in 2000
350
300
300
233
250
200
150
107
98
100
57
50
0
Heart
Disease
Cancer
Diabetes
Accidents
Homicide
BAR GRAPH: useful when you want to
compare data for several individual items
Favorite Television Shows among Teens
1%
4%
20%
Friends
45%
Will and Grace
Frasier
Dawson's Creek
Other
30%
PIE CHART: ideal for displaying data that are parts
of a whole.
(CHAPTER 2, sections 2.1 & 2.4)
MATTER = ANYTHING WITH MASS
AND VOLUME
Elements
Pure
Substances
Compounds
Matter
Homogeneous
Mixtures
Heterogeneous
Everything that is, is made up of matter.
From the very large...
To the very small...
Properties of Matter can be…
● Extensive properties: depend on the
AMOUNT of matter
-Example: Mass, Volume
● Intensive properties: depend on the
TYPE of matter
-Example: Absorbancy, Density
STATES OF MATTER:
● SOLID
● LIQUID
● GAS
SOLIDS:
● Definite shape?
● YES
● Definite volume?
● YES
● Molecules in a solid are tightly packed and
constantly vibrating.
LIQUIDS:
● Definite shape?
● NO
● Definite volume?
● YES
● Some liquids flow more easily than others. The
resistance of a liquid to flow is called viscosity.
– Honey has a high viscosity compared to water.
GASES:
● Definite shape?
● NO
● Definite volume?
● NO
● The particles in a gas are spread very far apart,
but can be compressed by pumping them into a
restricted volume.
Physical Properties:
● Physical properties: characteristics that can
be observed without changing the identity of the
substance.
● Examples:
-mass
-volume
-color
-shape
-texture
-density
-melting pt.
-boiling pt.
-magnetism
Physical Changes:
● Physical change: a change in the physical
form or properties of a substance that
occurs without a change in composition.
● Examples:
-melting
-freezing
-grinding
-dissolving
-bending
-tearing
-crushing
-boiling
Phase Changes:
● Changes in phase are examples of
physical changes.
● Melting: solid  liquid
● Freezing: liquid  solid
● Vaporization: liquid  gas
● Condensation: gas  liquid
● Sublimation: solid  gas
Chemical Properties:
● Chemical property: describes a
substance’s ability to change into a
different substance.
● Examples:
-flammability
-reactivity
Chemical Changes:
● Chemical change: occurs when a
substance changes composition by
forming one or more new
substances. (bonds are broken and
bonds are formed)
What is a Chemical Reaction?
● Chemical Reaction – one or more
substances change into new substances
● Process involves reactants and products
● Reactant – a starting substance in a
chemical reaction
● Product – a substance formed in a chemical
reaction
What is a Chemical Reaction?
● Example:
Nitrogen and hydrogen gas can react to form
ammonia under certain conditions.
Reactants
N2(g)
+
Yield
H2(g)

Products
NH3(g)
How Can You Tell Whether or Not a
Chemical Reaction Has Taken Place?
● Chemical Change – alters a given
material by changing its chemical
composition
● Examples: burn, rust, decompose,
corrode, explode
Other Indicators of a
CHEMICAL CHANGE:
-change in heat
-change in color
-change in odor
-light is given off
-formation of a gas
-formation of a solid
-irreversibility
Evaporation is a physical
change
Breaking is a physical
change.
Boiling is a change of state,
and therefore a physical
change!
Rusting is a Chemical
Change
Burning is a Chemical Change
CONSERVATION:
● Law of Conservation of Matter
(Mass): in a physical change or a
chemical reaction, matter is neither
created nor destroyed; it is conserved
Matter MUST be conserved; it’s
the LAW!