Chemical Reactions
Table of Contents
Observing Chemical Change
Describing Chemical Reactions
Controlling Chemical Reactions
Fire and Fire Safety
Chemical Reactions - Observing Chemical Change
Properties and Changes in Matter
Matter can undergo both physical change and
chemical change.
Chemical Reactions - Observing Chemical Change
Properties and Changes in Matter
Chemical changes occur when bonds break and new bonds
form.
Chemical Reactions - Observing Chemical Change
Energy in Chemical Changes
A student places two substances
in a flask and measures the
temperature once per minute
while the substances react. The
student plots the time and
temperature data and creates
the graph at left.
Chemical Reactions - Observing Chemical Change
Energy in Chemical Changes
Reading Graphs:
What was the temperature in
the flask at 4 minutes? When
was the first time the
temperature was at 6ºC?
At 4 minutes the temperature
in the flask was about 23ºC.
The first time the temperature
was 6ºC was at about 7
minutes.
Chemical Reactions - Observing Chemical Change
Energy in Chemical Changes
Calculating:
How many degrees did the
temperature drop between
2 minutes and 5 minutes?
20ºC
Chemical Reactions - Observing Chemical Change
Energy in Chemical Changes
Interpreting Data:
Is the reaction endothermic or
exothermic? Explain.
The reaction was
endothermic; it absorbed
thermal energy from the
reaction mixture, causing the
temperature to drop.
Chemical Reactions - Observing Chemical Change
Energy in Chemical Changes
Inferring:
At what temperature did the
reaction stop? How can you
tell?
The reaction stopped at about
2ºC. You can tell because that
is the lowest temperature
reached.
Chemical Reactions - Observing Chemical Change
Energy in Chemical Changes
Drawing Conclusions:
Suppose the temperature in
the flask increased instead of
decreased as the reaction
occurred. In terms of energy,
what kind of reaction would it
be? Explain.
If the temperature increased,
the reaction would be
exothermic; an exothermic
reaction is one in which
energy is released.
Chemical Reactions - Observing Chemical Change
Asking Questions
Before you read, preview the red headings. In a graphic
organizer like the one below, ask a what or how question for
each heading. As you read, write answers to your questions.
Properties and Changes of Matter
Question
Answer
What are physical
Physical properties are
properties of matter?
characteristics that can be
observed without changing
one substance into another.
What is the evidence for
The evidence for chemical
chemical reactions?
reactions is the formation of
new substances and
changes in energy.
Chemical Reactions - Observing Chemical Change
Links on Chemical Changes
Click the SciLinks button for links on chemical changes.
Chemical Reactions
End of Section:
Observing
Chemical
Change
Chemical Reactions - Describing Chemical Reactions
Describing Chemical Reactions
Cellular phone messages make use of symbols and
abbreviations to express ideas in shorter form. Similarly,
chemists often use chemical equations in place of words.
Chemical Reactions - Describing Chemical Reactions
What Are Chemical Equations?
Chemical equations use chemical formulas and other
symbols instead of words to summarize a reaction.
Chemical Reactions - Describing Chemical Reactions
Chemical Formulas
The formula of a compound identifies
the elements in the compound and the
ratios in which their atoms are present.
Chemical Reactions - Describing Chemical Reactions
Conservation of Mass
The principle of conservation of mass states that in a
chemical reaction, the total mass of the reactants must equal
the total mass of the products.
Chemical Reactions - Describing Chemical Reactions
Balancing Chemical Equations
To describe a reaction accurately, a chemical equation must
show the same number of each type of atom on both sides of
the equation.
Chemical Reactions - Describing Chemical Reactions
Balancing Equations Activity
Click the Active Art button to open a browser window and
access Active Art about balancing equations.
Chemical Reactions - Describing Chemical Reactions
Balancing Chemical Equations
Magnesium metal (Mg) reacts
with oxygen gas (O2), forming
magnesium oxide (MgO). To
write a balanced equation for
this reaction, first write the
equation using the formulas of
the reactants and products, then
count the number of atoms of
each element.
Chemical Reactions - Describing Chemical Reactions
Balancing Chemical Equations
Balancing Chemical Equations:
Balance the equation for the
reaction of sodium metal (Na)
with oxygen gas (O2), forming
sodium oxide (Na2O).
Chemical Reactions - Describing Chemical Reactions
Balancing Chemical Equations
Balancing Chemical Equations:
Balance the equation for the
reaction of tin (Sn) with
chlorine gas (Cl2), forming tin
chloride (SnCl2).
Chemical Reactions - Describing Chemical Reactions
Classifying Chemical Reactions
Many chemical reactions can be classified in one of three
categories: synthesis, decomposition, or replacement.
Chemical Reactions - Describing Chemical Reactions
Building Vocabulary
Using a word in a sentence helps you think about how best
to explain the word. After you read the section, reread the
paragraphs that contain definitions of Key Terms. Use the
information you have learned to write a meaningful sentence
using each Key Term.
Key Terms:
closed system
chemical
equation
replacement
reactant
coefficient
product
Examples:
In chemical
A
a closed system,
equationmatter
is a short,
is noteasy
allowed
way to
to enter
show or
a
Replacement is the process in which one element
chemical reaction.
leave.
replaces another in a compound or two elements in
substance
you
at the
a reaction is
A coefficient
is ahave
number
in
abeginning
chemicalofequation
different
compounds
trade
places.
a reactant.
telling
you how many atoms or molecules of a reactant
or
product
take part
in the reaction.
A new
substance
produced
in a reaction is a product.
synthesis
conservation of mass
Synthesis
means
combining
two
or during
more elements
or
Conservation
of mass
means
that
a chemical
compounds
to make
more complex
substance.
reaction, matter
is nota created
or destroyed.
open system
decomposition
In an open system,
matter
can enter
from
or escape
Decomposition
means
breaking
down
compounds
to the
surroundings.
into
simpler
products.
Chemical Reactions
End of Section:
Describing
Chemical
Reactions
Chemical Reactions - Controlling Chemical Reactions
Energy and Reactions
All chemical reactions need a certain amount of activation
energy to get things started.
Chemical Reactions - Controlling Chemical Reactions
Energy and Reactions
Both exothermic and endothermic reactions need energy to
get started.
Chemical Reactions - Controlling Chemical Reactions
Rates of Chemical Reactions
The cells in your body (as in all living
things) contain biological catalysts called
enzymes. At the end of a reaction, an
enzyme molecule is unchanged.
Chemical Reactions - Controlling Chemical Reactions
Relating Cause and Effect
As you read, identify the factors that can cause the rate of a
chemical reaction to increase. Write the information in a
graphic organizer like the one below.
Causes
Increase in surface area
Effect
Increase in temperature
Increased rate of reaction
Increase in concentration
of reactants
Use of a catalyst
Chemical Reactions
Data Sharing Lab
Click the PHSchool.com button for an activity about sharing
data for the Skills Lab Temperature and Enzyme Activity.
Chemical Reactions - Controlling Chemical Reactions
Exothermic and Endothermic Reactions
Click the Video button to watch a movie about exothermic
and endothermic reactions.
Chemical Reactions
End of Section:
Controlling
Chemical
Reactions
Chemical Reactions - Fire and Fire Safety
Understanding Fire
Three things are necessary to
start and maintain a fire–fuel,
oxygen, and heat.
Chemical Reactions - Fire and Fire Safety
Understanding Fire
The fire triangle can be controlled
in the grill. If any part of the fire
triangle is missing, the fire will
not continue.
Chemical Reactions - Fire and Fire Safety
Home Fire Safety
If you know how to
prevent fires in your
home and what to do
if a fire starts, you are
better prepared to
take action.
Chemical Reactions - Fire and Fire Safety
Using Prior Knowledge
Before you read, write what you know about fire safety in a
graphic organizer like the one below. As you read, write what
you learn.
What You Know
1. A fire needs fuel to burn.
2. A fire need oxygen to burn.
3. All homes should have smoke detectors.
What You Learned
1. Fire is a result of a combustion reaction.
2. The most deadly fires start with cigarettes.
3. Baking soda can be used to put out small fires.
Chemical Reactions - Fire and Fire Safety
Links on Fire Safety
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Chemical Reactions
End of Section:
Fire and Fire
Safety
Chemical Reactions
Graphic Organizer
Chemical
reactions
can be
Endothermic
reactions
are written as
Exothermic
reactions
Equations
balanced with
which require
Activation
energy
written using
Chemical
symbols
Coefficients
Arrows and
plus signs
Chemical Reactions
End of Section:
Graphic Organizer