Transcript CHEMICAL CHANGE Chapter Seventeen: Chemical Change 17.1 Chemical Reactions 17.2 Balancing Equations 17.3 Classifying Reactions.

CHEMICAL CHANGE
Chapter Seventeen: Chemical
Change
17.1 Chemical Reactions
17.2 Balancing Equations
17.3 Classifying Reactions
Chapter 17.1 Learning Goals
Describe how energy is involved in
chemical changes.
Identify evidence that a chemical
change has occurred.
Explain what happens during
chemical reactions.
Investigation 17A
Chemical Equations
Key Question:
How are atoms conserved in a chemical
reaction?
17.1 Chemical Reactions
A chemical reaction is
the process of breaking
of chemical bonds in
one or more
substances, and the
reforming of new
bonds to create new
substances.
When you make pizza,
which changes are
physical and which are
chemical changes?
17.1 Chemical Reactions
The process of making pizza involves some
physical changes (like chopping vegetables).
The processes used by yeast in the dough or
by the gas stove to bake the pizza are
chemical changes.
17.1 Evidence of chemical change
Four indicators of
chemical change are:
1. Formation of new gas
2. Formation of new
solid
3. Release of energy
(heat or light)
4. Color change
17.1 Products and reactants
 In chemical reactions, you start
with reactants that are combined to
make products.
 The reactants are the starting
substances.
 The products are the new
substances which result from the
chemical reaction.
17.1 Reactants and products
In the reaction, methane (a natural gas) is
burned or combusted.
Some energy is added to get the reaction
started.
17.1 Reaction symbols
The small symbols
in the parentheses
(s, l, g, aq) next to
each chemical
formula indicate the
phase of each
substance in the
reaction.
Chapter Seventeen: Chemical
Change
17.1 Chemical Reactions
17.2 Balancing Equations
17.3 Classifying Reactions
Chapter 17.2 Learning Goals
Relate a balanced chemical
equation to the law of
conservation of mass.
Determine the formula and molar
masses of chemical compounds.
Write and balance chemical
equations.
Investigation 17B
Conservation of Mass
Key Question:
How do scientists describe what happens in a
chemical reaction?
17.2 Balancing Equations
Antoine Laurent Lavoisier, established an
important principal based on his
experiments with chemical reactions.
He stated that the total mass of the
products of a reaction is equal to the total
mass of the reactants.
The law of conservation of mass holds true
for even a burning mass of wood.
17.2 Balancing Equations
The combined mass of the burning
wood and oxygen is converted into
carbon dioxide and water.
17.2 Conservation of mass
Lavoisier showed
that a closed system
must be used when
studying chemical
reactions.
When chemicals are
reacted in a closed
container, you can
show that the mass
before and after the
reaction is the same.
17.2 Formula mass
The sum of the atomic mass values of
the atoms in a chemical formula is
called the formula mass.
17.2 Avogadro’s Number
The Avogadro number was named in honor
of Amedeo Avogadro who discovered that a
mole of any gas under the same conditions
has the same number of molecules.
Johann Josef Loschmidt, a German
physicist, named and discovered the
Avogadro number.
Loschmidt realized that a mole of any
substance—be it a gas, liquid, or solid—
contains 6.02 x 1023 atoms or molecules.
17.2 Molar Mass
The mass (in grams) of one mole of a
compound is called its molar mass.
Solving Problems
What is the molar mass of one mole of
CaCO3?
1. Looking for:
 … molar mass of CaCO3
2. Given
 … chemical formula
3. Relationships:
 no. amu in formula = molar mass in grams
Solving Problems
4. Solution
 Use periodic table and round values as
needed.
Formula mass CaC03 = 100.19 g
1 mole CaC03 = 100.19 g CaCO3
17.2 Chemical Equations
When a chemical reaction is written
using chemical formulas and symbols,
it is called a chemical equation.
17.2 Chemical equations
An arrow is always included between
reactants and products.
It means “to produce” or “to yield.”
to produce
Reactants
Products
“Methane combines with oxygen gas to produce
carbon dioxide gas and water vapor.”
17.2 Numbers in equations
17.2 Balancing equations
The law conservation of mass is applied by
balancing the number and type of atoms on
either side of the equation.
17.2 Balancing equations
 Counting atoms is necessary to
balance an equation.
How many carbon atoms?
How many hydrogen atoms?
How many oxygen atoms?
17.2 Balancing chemical
equations
A balanced chemical equation has the same
number of each type of atom on the product
side and the reactant side.
To balance the equation, we add another
water molecule to the product side and add
another oxygen molecule to the reactant
side.
We can practice balancing equations using
CPO periodic table tiles and pencil and
paper.
17.2 Steps for balancing
1. If not provided, write the word form of the
equation.
 Calcium carbonate reacts with hydrochloric acid
to produce calcium chloride, carbon dioxide and
water.
17.2 Steps for balancing
2. If not provided, write the chemical
equation from the word form.
17.2 Steps for balancing
3. Count the number of each type of
atom on both sides.
17.2 Steps for balancing
4. Add coefficients to balance the
equation.
Solving Problems
 In this reaction, chalcocite (a
mineral) reacts with oxygen in the
presence of heat. The products
are a type of copper oxide and
sulfur dioxide. Balance this
equation:
Cu2S + O2 → Cu2O + SO2
Solving Problems
1. Looking for:
 …the coefficients for each molecule
2. Given
 … chemical formulas which show types
and no. of atoms
Solving Problems
3. Relationships
 Coefficients can be added in front of any
chemical formula in a chemical equation.
 When a coefficient is added in front of a
chemical formula, all atoms in that
formula are multiplied by that number.
 Use common denominators to help choose
coefficients to try.
Solving Problems
4. Solution- Trial and error
Chapter Seventeen: Chemical
Change
17.1 Chemical Reactions
17.2 Balancing Equations
17.3 Classifying Reactions
Chapter 17.3 Learning Goals
Classify reactions based on how atoms
combine to create new substances.
Discuss applications of polymer
science.
Study examples of combustion
reactions.
Investigation 17C
Classifying Chemical Reactions
Key Question:
How can you predict the products of a
chemical reaction?
17.3 Addition reactions
The process of creating large
molecules from small ones is called
polymerization.
17.3 Addition reactions
In an addition reaction, two or more
substances combine to form a new
compound.
17.3 Addition reaction
A
+
B -----> AB
Fe (s) + O2 (g) -----> Fe2O3 (s)
Remember to balance!
4 Fe + 3 O2
-----> 2 Fe2O3
17.3 Decomposition reactions
A chemical reaction in which a single
compound is broken down to produce
two or more smaller compounds is
called a decomposition reaction.
17.3 Decomposition reaction
AB
-energy->
A
+
B
2 H2O (l) -electricity-> 2 H2 (g) + O2 (g)
2 NaHCO3
(s)
-heat->
Na2O (s) + CO2 + 2 H2 (g)
(g)
17.3 Single Displacement
In a single-displacement reaction, one
element replaces a similar element in a
compound.
17.3 Single Displacement
A + XB
Fe +
Cu Cl2
----->
+
----->
----->
+
+
17.3 Double Displacement
In a double-displacement reaction, ions from
two compounds in solution exchange places
to produce two new compounds.
One of the compounds formed is usually a
precipitate that settles out of the solution, a
gas that bubbles out of the solution, or a
molecular compound such as water.
17.3 Double Displacement
AB
+
CD ---> AC + BD
Pb(NO3)2 + 2 KI ---> PbI2 + 2
KNO3
17.3 Precipitation reactions
A precipitate is a new
solid product that comes
out of solution in a
chemical reaction.
The formation of a cloudy
precipitate is evidence
that a double-displacement
reaction has occurred.
17.3 Precipitation
The limewater test for carbon dioxide
is a precipitation reaction.
17.3 Combustion reactions
A combustion reaction, also called
burning, occurs when a substance
such as wood, natural gas, or propane
combines with oxygen and releases a
large amount of energy in the form of
light and heat.
17.3 Combustion reactions
What do reactants
like wood, natural
gas, and propane
have in common?
17.3 Combustion
CxHy + O2 ---> CO2 + H2O +
energy
C6H12O6 + 6 O2 ---> 6 CO2 + 6 H2O
+ energy
Hydrogen Powered Cars
Scientists and engineers
from government agencies,
universities, and all of the
major automobile
manufacturers are
designing, building, and
testing hydrogen fuel cell
vehicles, also known as
FCVs.