Chemical Reactions: Reactants, Products, and Balancing Equations
Chapter 7 – Chemical
Chapter 7 – Chemical
Reactions
Reactions
Jennie L. Borders
Jennie L. Borders
Warm-Up Mar. 21
Warm-Up Mar. 21
1.
In a chemical reaction, what are the
substances to the left of the arrow called?
2.
When balancing equations, which
numbers are you allowed to add?
3.
What is a decomposition reaction?
Section 7.1 – Describing Reactions
Section 7.1 – Describing Reactions
In a
chemical reaction
, the substances that
undergo
change are called
reactants
.
The
new substances
formed as a result of
that change are called
products
.
Reactants
Products
Chemical Equations
Chemical Equations
A
chemical equation
is a representation of
a chemical reaction in which the
reactants
and products
are expressed in
formulas
.
The
law of conservation of mass
states
that mass is neither
created nor destroyed
in a chemical reaction.
Balancing Equations
Balancing Equations
In order to show that
mass
is
conserved
during a reaction, a
chemical equation
must be
balanced
.
You can
balance
a chemical equation by
changing the
coefficients
, the
numbers
that appear
before
the formulas.
As you
balance equations
, you should
never change the
subscripts
in a formula.
Balancing Equations
Balancing Equations
Balancing Equations
Balancing Equations
Balance the following equations.
Cu + O
2
CuO
H
2
+ Cl
2
HCl
H
2
O
2
H
2
O + O
2
2
Cu + O
2
2
CuO
H
2
+ Cl
2
2
HCl
2
H
2
O
2
2
H
2
O + O
2
Balancing Equations
Balancing Equations
Balance the following equations.
Mg + HCl
H
2
+ MgCl
2
C
2
H
4
+ O
2
CO
2
+ H
2
O
Mg +
2
HCl
H
2
+ MgCl
2
C
2
H
4
+
3
O
2
2
CO
2
+
2
H
2
O
Hints for Balancing Equations
Hints for Balancing Equations
Balance
hydrogen and oxygen
last.
Keep
polyatomic ions
together if possible.
If you have an
odd number
of atoms on
one side, you can multiply by
2
to make it
even.
Moles
Moles
Because
chemical reactions
often involve
large numbers
of small particles, chemists
use a counting unit called the
mole
to
measure
amounts
of substances.
1 mole = 6.02 x 10
23
particles
This number is called
Avogadro’s number
.
SKIP!
Section 7.1 Assessment
Section 7.1 Assessment
1.
What is the law of conservation of mass?
2.
Why does a chemical equation need to
be balanced?
3.
Why do chemists use the mole as a
counting unit?
4.
Is the following equation balanced?
2Na + Cl
2
2NaCl
SKIP!
Section 7.1 Assessment
Section 7.1 Assessment
5. Balance the following equation.
K + Br
2
KBr
6. Balance the following equation.
Mg + O
2
MgO
Warm-Up Mar. 25
Warm-Up Mar. 25
1.
Balance the following equation:
Na + O
2
Na
2
O
1.
What is the law of conservation of mass?
2.
What elements should you save until the
end when balancing?
Section 7.2 – Types of Reactions
Section 7.2 – Types of Reactions
Some general types of chemical reactions
are
synthesis reactions, decomposition
reactions, single-replacement reactions,
double-replacement reactions, and
combustion reactions
.
Synthesis
Synthesis
A
synthesis
reaction is a reaction in which
two or more
substances react to form a
single
substance.
A + B
AB
2Na + Cl
2
2NaCl
2H
2
+ O
2
2H
2
O
Decomposition
Decomposition
A
decomposition
reaction is a reaction in
which a
compound
breaks down into
two
or more
simpler substances.
AB
A + B
HgO
Hg + O
2
CaCO
3
CaO + CO
2
Single Replacement
Single Replacement
A
single-replacement
reaction is a reaction
in which
one element
takes the place of
another element in a
compound
.
A + BC
B + AC
Cu + 2AgNO
3
2Ag + Cu(NO
3
)
2
2K + 2H
2
O
H
2
+ 2KOH
Double Replacement
Double Replacement
A
double-replacement
reaction is one in
which two different
compounds
exchange
positive ions
and form
two
new
compounds.
AB + CD
AD + CB
Pb(NO
3
)
2
+ 2KI
PbI
2
+ 2KNO
3
CaCO
3
+ 2HCl
CaCl
2
+ H
2
CO
3
Combustion
Combustion
A
combustion
reaction is one in which a
substance reacts rapidly with
oxygen
,
often producing
heat and light
.
C
x
H
y
+ O
2
CO
2
+ H
2
O
CH
4
+ 2O
2
CO
2
+ 2H
2
O
C
6
H
12
O
6
+ 6O
2
6CO
2
+ 6H
2
O
Section 7.2 Assessment
Section 7.2 Assessment
1.
What are five general types of reactions?
2.
The synthesis of water is described by
the following reaction 2H
2
+ O
2
2H
2
O.
How is the decomposition of water
related to this reaction?
3.
Explain the difference between a single-
replacement reaction and a double-
replacement reaction.
Section 7.2 Assessment
Section 7.2 Assessment
4. When propane (C
3
H
8
) undergoes
combustion, what products are formed?
5. Identify the following reactions.
a. Pb(NO
3
)
2
+ 2HCl
PbCl
2
+ 2HNO
3
b. 2C
2
H
6
+ 7O
2
4CO
2
+ 6H
2
O
c. Ca + 2HCl
CaCl
2
+ H
2
d. 2SO
2
+ O
2
2SO
3
Warm-Up Mar. 26
Warm-Up Mar. 26
1.
How many reactants are in a
decomposition reaction?
2.
What 3 elements will you see in a
combustion reaction?
3.
What type is the following reaction?
2Zn + Li
2
O
Li + 2ZnO
Section 7.3 – Energy Changes in
Section 7.3 – Energy Changes in
Reactions
Reactions
Chemical energy
is the
energy stored in the
chemical bonds
of a
substance.
Chemical reactions involve
the
breaking of chemical
bonds
in the reactants and
the
formation of chemical
bonds
in the products.
Breaking and Forming Bonds
Breaking and Forming Bonds
Breaking
chemical bonds
requires
energy.
The
formation
of chemical bonds
releases
energy.
SKIP!
Energy in Chemical Reactions
Energy in Chemical Reactions
In a
chemical reaction
, energy is either
released or absorbed
.
Exothermic Reactions
Exothermic Reactions
A chemical reaction that
releases energy
to its surroundings is called an
exothermic
reaction
.
In
exothermic reactions
, the energy
released
as the products form is greater
than the energy
required
to break the
bonds in the reactants.
SKIP!
Endothermic Reactions
Endothermic Reactions
A chemical reaction that
absorbs
energy
from its surroundings is called an
endothermic reaction
.
In an
endothermic reaction
, more energy
is
required
to break the bonds in the
reactants than is
released
by the formation
of the products.
SKIP!
Law of Conservation of Energy
Law of Conservation of Energy
The
law of conservation of energy
states
that energy is neither
created nor
destroyed
in a chemical or physical
process.
Section 7.3 Assessment
Section 7.3 Assessment
1.
What happens to chemical bonds as a
chemical reaction occurs?
2.
How do chemical reactions involve
energy?
3.
Is the combustion of propane
endothermic or exothermic?
4.
Is energy created during an exothermic
reaction? Explain.
Section 7.3 Assessment
Section 7.3 Assessment
5. What bonds are broken when one
molecule of methane reacts with two
molecules of oxygen in the following
reaction:
CH
4
+ 2O
2
CO
2
+ 2H
2
O
SKIP!
Section 7.4 – Reaction Rates
Section 7.4 – Reaction Rates
A
reaction rate
is the rate at which
reactants
change
into products over time.
Reaction rates
tell how
fast
a reaction is
going.
SKIP!
Factors Affecting Reaction
Factors Affecting Reaction
Rates
Rates
Factors that affect reaction rates include
temperature, surface area, concentration,
stirring, and catalysts
.
Chemical reactions are based on the
collisions
of particles.
SKIP!
Temperature
Temperature
Generally, an increase in
temperature
will
increase the
reaction rate
, while a
decrease in temperature will
decrease
the
reaction rate.
Increasing the
temperature
of a substance
causes its
particles
to move faster which
causes more
collisions
.
SKIP!
Surface Area
Surface Area
An increase in
surface area
increases the
exposure
of reactants to one another.
The greater this
exposure
, the more
collisions
there are that involve reacting
particles
.
SKIP!
Stirring
Stirring
Stirring
the reactants
will generally
increase
the reaction rate.
Stirring
causes the
reactants to
combine
quickly, which causes
more
collisions
.
SKIP!
Concentration
Concentration
Concentration
refers to the
number of
particles
in a given volume.
Generally,
reaction rate
increases as
concentration
increases.
The
more particles
that are present in a
given volume, the more opportunities there
are for
collisions
involving those particles.
SKIP!
Catalysts
Catalysts
A
catalyst
is a substance that affects the
reaction rate
without being used up in the
reaction.
Since a
catalyst
is neither a
reactant nor a
product
, it is written over the
arrow
.
2SO
2
+ O
2
2SO
3
V
2
O
5
SKIP!
Section 7.4 Assessment
Section 7.4 Assessment
1.
What does a reaction rate tell you?
2.
What five factors affect reaction rate?
3.
Explain why reactions take place faster at
higher temperatures.
4.
How does a catalyst make a reaction go
faster?
SKIP!
Section 7.4 Assessment
Section 7.4 Assessment
5. Explain why hamburger meat lasts longer
in the freezer than in refrigerator.
6. The reaction between magnesium and
hydrochloric acid produces hydrogen. If you
increase the concentration of HCl, the
reaction takes place faster. Could HCl be
considered a catalyst for this reaction?
Explain.
SKIP!
Chemical reactions involve reactants that transform into products. Balancing equations is essential to ensure the conservation of mass. Learn about decomposition reactions, chemical equations, and methods to balance equations effectively.
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Presentation Transcript
Chapter 7 Chemical Reactions Jennie L. Borders
Warm-Up Mar. 21 1. In a chemical reaction, what are the substances to the left of the arrow called? 2. When balancing equations, which numbers are you allowed to add? 3. What is a decomposition reaction?
Section 7.1 Describing Reactions In a chemical reaction, the substances that undergo change are called reactants. The new substances formed as a result of that change are called products. Reactants Products
Chemical Equations A chemical equation is a representation of a chemical reaction in which the reactants and products are expressed in formulas. The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction.
Balancing Equations In order to show that mass is conserved during a reaction, a chemical equation must be balanced. You can balance a chemical equation by changing the coefficients, the numbers that appear before the formulas. As you balance equations, you should never change the subscripts in a formula.
Balancing Equations Balance the following equations. Cu + O2 CuO 2Cu + O2 2CuO H2 + Cl2 2HCl H2 + Cl2 HCl H2O2 H2O + O2 2H2O2 2H2O + O2
Balancing Equations Balance the following equations. Mg + HCl H2 + MgCl2 Mg + 2HCl H2 + MgCl2 C2H4 + O2 CO2 + H2O C2H4 + 3O2 2CO2 + 2H2O
Hints for Balancing Equations Balance hydrogen and oxygen last. Keep polyatomic ions together if possible. If you have an odd number of atoms on one side, you can multiply by 2 to make it even.
Moles Because chemical reactions often involve large numbers of small particles, chemists use a counting unit called the mole to measure amounts of substances. 1 mole = 6.02 x 1023 particles This number is called Avogadro s number.
Section 7.1 Assessment 1. What is the law of conservation of mass? 2. Why does a chemical equation need to be balanced? 3. Why do chemists use the mole as a counting unit? 4. Is the following equation balanced? 2Na + Cl2 2NaCl SKIP!
Section 7.1 Assessment 5. Balance the following equation. K + Br2 KBr 6. Balance the following equation. Mg + O2 MgO
Warm-Up Mar. 25 1. Balance the following equation: Na + O2 Na2O 1. What is the law of conservation of mass? 2. What elements should you save until the end when balancing?
Section 7.2 Types of Reactions Some general types of chemical reactions are synthesis reactions, decomposition reactions, single-replacement reactions, double-replacement reactions, and combustion reactions.
Synthesis A synthesis reaction is a reaction in which two or more substances react to form a single substance. A + B AB 2Na + Cl2 2NaCl 2H2 + O2 2H2O
Decomposition A decomposition reaction is a reaction in which a compound breaks down into two or more simpler substances. AB A + B HgO Hg + O2 CaCO3 CaO + CO2
Single Replacement A single-replacement reaction is a reaction in which one element takes the place of another element in a compound. A + BC B + AC Cu + 2AgNO3 2Ag + Cu(NO3)2 2K + 2H2O H2 + 2KOH
Double Replacement A double-replacement reaction is one in which two different compounds exchange positive ions and form two new compounds. AB + CD AD + CB Pb(NO3)2 + 2KI PbI2 + 2KNO3 CaCO3 + 2HCl CaCl2 + H2CO3
Combustion A combustion reaction is one in which a substance reacts rapidly with oxygen, often producing heat and light. CxHy + O2 CO2 + H2O CH4 + 2O2 CO2 + 2H2O C6H12O6 + 6O2 6CO2 + 6H2O
Section 7.2 Assessment 1. What are five general types of reactions? 2. The synthesis of water is described by the following reaction 2H2 + O2 2H2O. How is the decomposition of water related to this reaction? 3. Explain the difference between a single- replacement reaction and a double- replacement reaction.
Section 7.2 Assessment 4. When propane (C3H8) undergoes combustion, what products are formed? 5. Identify the following reactions. a. Pb(NO3)2 + 2HCl PbCl2 + 2HNO3 b. 2C2H6 + 7O2 4CO2 + 6H2O c. Ca + 2HCl CaCl2 + H2 d. 2SO2 + O2 2SO3
Warm-Up Mar. 26 1. How many reactants are in a decomposition reaction? 2. What 3 elements will you see in a combustion reaction? 3. What type is the following reaction? 2Zn + Li2O Li + 2ZnO
Section 7.3 Energy Changes in Reactions Chemical energy is the energy stored in the chemical bonds of a substance. Chemical reactions involve the breaking of chemical bonds in the reactants and the formation of chemical bonds in the products.
Breaking and Forming Bonds Breaking chemical bonds requires energy. The formation of chemical bonds releases energy.
Energy in Chemical Reactions In a chemical reaction, energy is either released or absorbed.
Exothermic Reactions A chemical reaction that releases energy to its surroundings is called an exothermic reaction. In exothermic reactions, the energy released as the products form is greater than the energy required to break the bonds in the reactants. SKIP!
Endothermic Reactions A chemical reaction that absorbs energy from its surroundings is called an endothermic reaction. In an endothermic reaction, more energy is required to break the bonds in the reactants than is released by the formation of the products. SKIP!
Law of Conservation of Energy The law of conservation of energy states that energy is neither created nor destroyed in a chemical or physical process.
Section 7.3 Assessment 1. What happens to chemical bonds as a chemical reaction occurs? 2. How do chemical reactions involve energy? 3. Is the combustion of propane endothermic or exothermic? 4. Is energy created during an exothermic reaction? Explain.
Section 7.3 Assessment 5. What bonds are broken when one molecule of methane reacts with two molecules of oxygen in the following reaction: CH4 + 2O2 CO2 + 2H2O
Section 7.4 Reaction Rates A reaction rate is the rate at which reactants change into products over time. Reaction rates tell how fast a reaction is going.
Factors Affecting Reaction Rates Factors that affect reaction rates include temperature, surface area, concentration, stirring, and catalysts. Chemical reactions are based on the collisions of particles.
Temperature Generally, an increase in temperature will increase the reaction rate, while a decrease in temperature will decrease the reaction rate. Increasing the temperature of a substance causes its particles to move faster which causes more collisions.
Surface Area An increase in surface area increases the exposure of reactants to one another. The greater this exposure, the more collisions there are that involve reacting particles.
Stirring Stirring the reactants will generally increase the reaction rate. Stirring causes the reactants to combine quickly, which causes more collisions.
Concentration Concentration refers to the number of particles in a given volume. Generally, reaction rate increases as concentration increases. The more particles that are present in a given volume, the more opportunities there are for collisions involving those particles.
Catalysts A catalyst is a substance that affects the reaction rate without being used up in the reaction. Since a catalyst is neither a reactant nor a product, it is written over the arrow. V2O5 2SO2 + O2 2SO3
Section 7.4 Assessment 1. What does a reaction rate tell you? 2. What five factors affect reaction rate? 3. Explain why reactions take place faster at higher temperatures. 4. How does a catalyst make a reaction go faster?
Section 7.4 Assessment 5. Explain why hamburger meat lasts longer in the freezer than in refrigerator. 6. The reaction between magnesium and hydrochloric acid produces hydrogen. If you increase the concentration of HCl, the reaction takes place faster. Could HCl be considered a catalyst for this reaction? Explain.
