Conceptual Chemistry
UNIT 2 – MATTER AND
CHANGE
Objective 1
 Read and express information given in
chemical formulas.
What is matter?
 Matter: Anything that has mass and takes up
space.
Pure Substances
 Matter that has fixed composition and
properties.
 Cannot be broken down by physical methods.
Elements
 A substance that cannot be broken down by
chemical means.
 i.e. iron (Fe), carbon (C), oxygen (O), nitrogen (N)
Compounds
 A substance made of elements that are
chemically combined.
 i.e. water (H2O), salt (NaCl), sugar (C12H22O11)
Compounds
 Every compound is composed of the
elements it contains.
Chemical Formula
 Shows the type and number of atoms present
in a substance.
Chemical Formula
• In the chemical formula, subscripts show
how many atoms are in the compound.
C6H10N2O2
C=6
H= 10
N= 2
O= 2
Chemical Formula
 The large numbers in front of the chemical
formula, called coefficients, show the number
of particles.
3C6H10N2O2
C6H10N2O2 = 3 total
Practice Problems:
How atoms of each element are in the following?
1. CH4
2. AlCl3
3. 4 H2O
4. 10 Fe3P2
5. 6 Zn(NO3)2
6. Al2(SO3)3
Objective 2
 Classify matter as a pure substance or a
mixture.
Mixtures
 Matter that has compositions that are not
uniform or definite.
Mixtures
 Mixtures can be separated by physical means
into the substances that are mixed with in
them.
Homogeneous Mixtures
 Homo = same
 The composition is the same throughout
Examples
 Solid  Solid: Brass
(Zinc and Copper)
 Liquid  Liquid: Alcohol
(Ethanol and Water)
 Gas  Gas: Air
(Nitrogen and Oxygen)
 Solid (dissolves)  Liquid: Salt Water
(Sodium Chloride and Water)
 Gas (dissolves)  Liquid: Carbonation
(Carbon Dioxide and Water)
Heterogeneous Mixture
 Hetero = different
 The composition is different throughout.
Objective 3
 Distinguish between chemical and physical
changes, as well as chemical and physical
properties.
Practice Problems
Hetero or Homo Mixture
Tap Water :_______________
A Rock: ________________
Stainless Steel:________________
Brewed Coffee: ________________
Sand: ________________
Oatmeal: ________________
Dust Free Air: ________________
Rusty Metal: _________________
Why?
Properties of Matter
 Physical Properties: Can be measured without
changing the substance’s chemical composition.
 i.e. melting point, boiling point, density, solubility,
odor, hardness, color, etc.
 Chemical Properties: Potential reactivity of
substance with other substances. Can only be
measured by trying the reactions.
 i.e. Any particular reaction a substance undergoes.
Changes of Matter
 Physical Change
 Chemical Change
Physical Change
 Alters a substance without changing the
substance’s chemical composition.
 i.e. melting, boiling, cutting, smashing,
dissolving
Chemical Change
 Occur when one or more substances are
changed into another substance that have
different chemical compositions.
 i.e.
rusting, exploding, decomposing,
corroding, spoiling
Practice Problems
Chemical or Physical Property?
Chemical or Physical Change?
Tarnishes in Rain:
Lighting a firework:
Bends easily:
Boiling Pasta:
Decomposes:
Chewing gum:
Reusable/Recyclable:
Running your car:
Shiny:
Rolling your bike:
Not Flammable:
Melting a crayon:
Perishable Food:
Rusting a nail:
Freezable Food:
Opening a can of pop:
Objective 4
 Balancing chemical equations.
Chemical Equation
 Ex:
2 KClO3  2 KCl + 3 O2
 Describes the original beginning substances
(called reactants) using chemical formulas.
Then an arrow points to the newly created
substances (called products) using chemical
formulas again.
 Reactants  Products
Symbols
(s) =
+=
(l) =
=
(g) =
∆=
(aq) =
H2 (subscripts) =
2 H2 = (Coefficients) =
Balancing Equations
 The law of conservation of mass states that
matter cannot be created or destroyed. So,
the number of atoms reacting must equal the
number of atoms produced. However, a
chemical change rearranges these atoms into
new substances.
To balance equations, follow these
steps:
Count atoms on each side of the arrow. They
should be equal. If not, you need to balance
them.
2. Balance both sides by using coefficients.
Remember, they multiply through everything
inside of that compound. NEVER change
subscripts.
3. Double check work.
1.
Practice Problems
____ KClO3  ____ KCl + ____ O2
____AlBr3 + ____ K2SO4  ____ KBr + ____ Al2(SO4)3
____ C3H8 + ____ O2  ____ CO2 + ____ H2O
Objective 5
 Describing chemical reactions and
calculate percent yield and percent
error.
Error Calculations
 Error = experimental value – accepted value
 Magnitude of the value tells whether or not
the experimental value is too high or too low
 Accepted value: Accurate value based on a
reliable reference
 Experimental value: value measured in lab
 Percent Error = |
Error
| x 100%
Accepted Value
Percent Yield
 Used to determine completeness of a
reaction
 Actual Yield: actual amount of products
produced in an experiment
 Theoretical Yield: maximum amount of
products predicted from conservation of
mass
 Percent Yield = Actual Yield x 100%
Theoretical Yield