Chapter 6 Chemical Reactions Rates of Chemical Reactions

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Chapter 6 Chemical Reactions
Table of Contents
Chapter Preview
6.1 Observing Chemical Change
6.2 Describing Chemical Reactions
6.3 Controlling Chemical Reactions
6.4 Fire and Fire Safety
Chapter 6 Chemical Reactions
Chapter Preview Questions
1. Which of the following is an example of a physical change?
a. Wood burns and becomes ash.
b. A silver fork tarnishes.
c. Water boils and becomes water vapor.
d. Leaves decay over time.
Chapter 6 Chemical Reactions
Chapter Preview Questions
1. Which of the following is an example of a physical change?
a. Wood burns and becomes ash.
b. A silver fork tarnishes.
c. Water boils and becomes water vapor.
d. Leaves decay over time.
Chapter 6 Chemical Reactions
Chapter Preview Questions
2. When a forest burns, it
a. neither absorbs nor releases energy.
b. loses matter and energy.
c. absorbs energy.
d. releases energy.
Chapter 6 Chemical Reactions
Chapter Preview Questions
2. When a forest burns, it
a. neither absorbs nor releases energy.
b. loses matter and energy.
c. absorbs energy.
d. releases energy.
Chapter 6 Chemical Reactions
Chapter Preview Questions
3. Fe, which stands for iron, is a
a. chemical symbol.
b. chemical equation.
c. atomic number.
d. name.
Chapter 6 Chemical Reactions
Chapter Preview Questions
3. Fe, which stands for iron, is a
a. chemical symbol.
b. chemical equation.
c. atomic number.
d. name.
Chapter 6 Chemical Reactions
Chapter Preview Questions
4. The ease and speed with which an element combines with
other elements is called its
a. atomic number.
b. chemical property.
c. physical property.
d. reactivity.
Chapter 6 Chemical Reactions
Chapter Preview Questions
4. The ease and speed with which an element combines with
other elements is called its
a. atomic number.
b. chemical property.
c. physical property.
d. reactivity.
Chapter 6 Chemical Reactions
What happens during a chemical reaction?
Suppose you fill a sealable bag
with ice cubes, and you allow the
ice to melt. How would the mass
of the bag and ice before
melting compare to the mass of
the water and the bag after
melting? Explain your answer.
Chapter 6 Chemical Reactions
Section 1: Observing Chemical
Change
Standard 8.5.a: Students know reactant
atoms and molecules interact to form
products with different chemical
properties.
Standard 8.5.c: Students know chemical
reactions usually liberate heat or absorb
heat.
Chapter 6 Chemical Reactions
Matter and Change
How can changes in
matter be described?
Physical Property
Chemical Property
Changes in matter can be
described in terms of physical
changes and chemical changes
A characteristic of a substance
that can be observed with out
changing into another substance.
A characteristic of a substance
that describes its ability to change
into other substances.
Chapter 6 Chemical Reactions
Matter and Change
Physical Change
Any change that alters the form or
appearance of a substance but
does not make the substance into
another substance.
Chapter 6 Chemical Reactions
Matter and Change
Chemical Property
A characteristic of a substance
that describes its ability to change
into other substances.
Chapter 6 Chemical Reactions
Properties and Changes in Matter
Chemical changes occur when bonds break and new bonds
form.
Chapter 6 Chemical Reactions
Evidence for Chemical Reactions
How can you tell when a
chemical reaction occurs?
Precipitate
Endothermic Reaction
Exothermic Reaction
Chemical reactions involve
changes in properties and
changes in energy that you can
observe.
A solid that forms from solution
during a chemical reaction.
The making and breaking of bonds
results in a net absorption of
energy
The making and breaking of bonds
results in a net release of energy.
Chapter 6 Chemical Reactions
Evidence for Chemical Reactions
How can you tell when a
chemical reaction occurs?
4 Observations of
Chemical Change
1. There is a formation of gas
which can be seen by a fizzing
or bubbling.
2. The reaction will cause heat,
light, or odor to be emitted
3. A color change is produced.
4. A solid is formed during the
change.
Chapter 6 Chemical Reactions
Section 1 Quick Quiz
What happens when chemical bonds break and new
bonds form?
A.A physical change
B.A chemical reaction
C.Matter is destroyed
D.Surface area increases
Answer: B – A chemical reaction
Chapter 6 Chemical Reactions
Section 1 Quick Quiz
A chemical reaction that absorbs energy in the form of
heat is described as
A. endothermic
B. exothermic
C. combustion
D. unbalanced
Answer: A - endothermic
Chapter 6 Chemical Reactions
Section 1 Quick Quiz
Every chemical reaction involves a change in
A. mass
B. energy
C. concentration
D. state
Answer: B - energy
Chapter 6 Chemical Reactions
Section 1 Quick Quiz
One example of a chemical change is
A.filtering
B.burning wood
C.boiling water
D.crushing a can
Answer: B – burning wood
Chapter 6 Chemical Reactions
Section 1 Quick Quiz
Anything that has mass and takes up space is
considered
A. matter
B. energy
C. chemistry
D. endothermic
Answer: A - matter
Chapter 6 Chemical Reactions
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.
Chapter 6 Chemical Reactions
Energy in Chemical Changes
Reading Graphs:
What was the temperature in
the flask at 3 minutes? When
was the first time the
temperature was at 6ºC?
At 3 minutes the temperature
in the flask was about 30ºC.
The first time the temperature
was 6ºC was at about 7
minutes.
Chapter 6 Chemical Reactions
Energy in Chemical Changes
Calculating:
How many degrees did the
temperature drop between
2 minutes and 5 minutes?
About 20ºC
Chapter 6 Chemical Reactions
Energy in Chemical Changes
Interpreting Data:
Is the reaction endothermic or
exothermic? Explain.
The reaction was
endothermic, because it
absorbed thermal energy
from the reaction mixture,
causing the temperature to
drop.
Chapter 6 Chemical Reactions
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.
Chapter 6 Chemical Reactions
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
instead, the reaction would be
exothermic, because an
exothermic reaction is one in
which energy is released.
Chapter 6 Chemical Reactions
Section 2: Describing Chemical Reactions
Standard 8.5.b: Students know the idea
of atoms explains the conservation of
matter. In chemical reactions the number
of atoms stays the same no matter how
they are arranged, so their total mass
stays the same.
Chapter 6 Chemical Reactions
What Are Chemical Equations?
What information does
a chemical equation
contain?
Chemical equations use chemical
formulas and other symbols
instead of words to summarize a
reaction.
Chapter 6 Chemical Reactions
Conservation of Matter
The principle of conservation of matter states that in a
chemical reaction, the total mass of the reactants must equal
the total mass of the products.
Chapter 6 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.
Chapter 6 Chemical Reactions
Balancing Chemical Equations
Magnesium (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.
Chapter 6 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).
Chapter 6 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).
Chapter 6 Chemical Reactions
Balancing Chemical Equations
http://education.jlab.org/elementbal
ancing/index.html
Chapter 6 Chemical Reactions
Classifying Chemical Reactions
Many chemical reactions can be classified in one of three
categories: synthesis, decomposition, or replacement.
Chapter 6 Chemical Reactions
Section 2 Quick Quiz
CaCO represents a chemical
A. symbol.
B. subscript.
C. formula.
D. reaction.
Answer: C - formula
Chapter 6 Chemical Reactions
Section 2 Quick Quiz
A chemical equation that shows the same number of
each kind of atom on both sides of the equation is said
to be
A. balanced.
B. unbalanced.
C. an incomplete reaction.
D. a replacement reaction.
Answer: A - balanced
Chapter 6 Chemical Reactions
Section 2 Quick Quiz
A bottle of hydrogen peroxide that eventually turns into
a bottle of water and oxygen gas is an example of a
A. replacement reaction.
B. precipitate reaction.
C. decomposition reaction.
D. synthesis reaction.
Answer: C - decomposition
Chapter 6 Chemical Reactions
Section 2 Quick Quiz
The substances listed on the left side of a chemical
equation are the
A. coefficients.
B. products.
C. reactants.
D. precipitates.
Answer: C - reactants
Chapter 6 Chemical Reactions
Section 2 Quick Quiz
In a chemical equation, numbers often appear in front of
a chemical formula. These numbers tell you the
A.number of molecules in each atom in the reaction.
B.number of molecules or atoms of each substance in
the reaction.
C.number of elements in the reaction.
D.number of atoms in each molecule in the reaction.
Answer: B – number of molecules or atoms of each
substance in the reaction
Chapter 6 Chemical Reactions
Section 3: Controlling Chemical Reactions
Standard 8.5.a: Students know reactant
atoms and molecules interact to form
products with different chemical
properties.
Standard 8.5.c: Students know chemical
reactions usually liberate heat or absorb
heat.
Chapter 6 Chemical Reactions
Energy and Reactions
How is activation energy
related to chemical
reactions?
All chemical reactions require a
certain amount of activation energy
to get started.
Activation Energy
The minimum amount of energy
needed to start a chemical reaction.
Potential Energy
Stored energy that results from the
position or shape of an object.
Kinetic Energy
Energy that an object has due to its
motion.
Chapter 6 Chemical Reactions
Energy and Reactions
All chemical reactions require a certain amount of activation
energy to get things started.
Chapter 6 Chemical Reactions
Energy and Reactions
Exothermic Reaction
A reaction that releases energy in
the form of heat.
Endothermic Reaction
A reaction that absorbs energy in
the form of heat.
Chapter 6 Chemical Reactions
Energy and Reactions
Both exothermic and endothermic reactions need energy to
get started.
Chapter 6 Chemical Reactions
Rates of Chemical Reactions
What factors affect the
rate of a chemical
reaction?
Catalyst
Inhibitor
Enzyme
Factors that affect rates of reaction
include:
 surface area;
 temperature;
 concentration; and
 the presence of catalysts and
inhibitors.
A material that increases the rate of
reaction by lowering the activation
energy.
A material used to decrease the rate
of reaction.
Biological catalysts found in the
cells of the body.
Chapter 6 Chemical Reactions
Rates of Chemical Reactions
The cells in your body (as in all living
things) contain biological catalysts called
enzymes. After a reaction, an enzyme
molecule is unchanged.
Chapter 6 Chemical Reactions
Section 3 Quick Quiz
The minimum amount of energy that has to be added to
start a reaction is the
A.exothermic energy.
B.endothermic energy.
C.activation energy.
D.chemical energy.
Answer: C – activation energy
Chapter 6 Chemical Reactions
Section 3 Quick Quiz
Chemicals that act as biological catalysts by speeding
up reactions in living things are
A. enzymes.
B. inhibitors.
C. reactants.
D. fuels.
Answer: A - enzymes
Chapter 6 Chemical Reactions
Section 3 Quick Quiz
A material used to decrease the rate of a chemical
reaction is a(n)
A. catalyst.
B. enzyme.
C. fuel.
D. inhibitor.
Answer: D - inhibitor
Chapter 6 Chemical Reactions
Section 4: Fire and Fire Safety
Standard 8.5.c: Students know chemical
reactions usually liberate heat or absorb
heat.
Chapter 6 Chemical Reactions
Understanding Fire
What are the three
things necessary
to maintain a fire?
•
•
•
•
Three things
necessary to start
and maintain a fire
are:
fuel
oxygen
heat
Chapter 6 Chemical Reactions
Understanding Fire
The fire triangle can be controlled
in the grill. If any part of the fire
triangle is missing, a fire will not
continue.
Chapter 6 Chemical Reactions
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.
The best form of fire
safety is prevention.
Chapter 6 Chemical Reactions
Section 3 Quick Quiz
In what way can a fire be brought under control?
A.Add fuel.
B.Add oxygen.
C.Remove oxygen.
D.Remove carbon dioxide.
Answer: C – Remove oxygen
Chapter 6 Chemical Reactions
Section 3 Quick Quiz
What is the best form of fire safety?
A.a water hose
B.an extinguisher
C.the fire department
D.fire prevention
Answer: D – fire prevention
Chapter 6 Chemical Reactions
Section 3 Quick Quiz
The best way to put out a small kitchen fire is to
A.blow it out
B.use a garden hose
C.turn off the appliances
D.cover it or use a home fire extinguisher
Answer: D – cover it or use a home fire extinguisher
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