Eighth Grade Physical
Science-Types of Reactions
Ray Legge
Jean Brainard, Ph.D.
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AUTHORS
Ray Legge
Jean Brainard, Ph.D.
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Printed: February 20, 2014
iii
Contents
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Contents
1
Synthesis Reactions
1
2
Decomposition Reactions
4
3
Replacement Reactions
7
4
Combustion Reactions
11
5
Endothermic Reactions
14
6
Exothermic Reactions
17
7
Conservation of Energy in Chemical Reactions
20
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C HAPTER
Chapter 1. Synthesis Reactions
1
Synthesis Reactions
• Define synthesis reaction.
• Describe an example of a synthesis reaction.
In this photo of Los Angeles, California, the air over the city is brown with smog. A major component of smog
is nitrogen dioxide, which is a toxic gas with a sharp odor. Nitrogen dioxide can irritate the eyes and throat and
trigger asthma attacks. Where does this poisonous gas come from? It forms when nitric oxidesources such as car
exhaustwith oxygen in the air. This reaction is a synthesis reaction.
What Is a Synthesis Reaction?
A synthesis reaction occurs when two or more reactants combine to form a single product. A synthesis reaction can
be represented by the general equation:
A+B→C
In this equation, the letters A and B represent the reactants that begin the reaction, and the letter C represents the
product that is synthesized in the reaction. The arrow shows the direction in which the reaction occurs.
Q: What is the chemical equation for the synthesis of nitrogen dioxide (NO2 ) from nitric oxide (NO) and oxygen
(O2 )?
A: The equation for this synthesis reaction is:
2NO + O2 → 2NO2
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Examples of Synthesis Reactions
Another example of a synthesis reaction is the combination of sodium (Na) and chlorine (Cl) to produce sodium
chloride (NaCl). This reaction is represented by the chemical equation:
2Na + Cl2 → 2NaCl
Sodium is a highly reactive metal, and chlorine is a poisonous gas. Both elements are pictured in the Figure 1.1. The
compound they synthesize has very different properties. Sodium chloride is commonly called table salt, which is
neither reactive nor poisonous. In fact, salt is a necessary component of the human diet. You can see more examples
of synthesis reactions at this URL: http://www.youtube.com/watch?v=dxlWtsFinTM
FIGURE 1.1
Summary
• A synthesis reaction occurs when two or more reactants combine to form a single product. This type of
reaction is represented by the general equation: A + B → AB.
• An example of a synthesis reaction is the combination of sodium (Na) and chlorine (Cl) to produce sodium
chloride (NaCl). This reaction is represented by the chemical equation: 2Na + Cl2 → 2NaCl.
Vocabulary
• synthesis reaction: Chemical reaction in which two or more reactants combine to form a single product.
Practice
Watch the two-video sequence on synthesis reactions at the following URLs, and then answer the questions below.
http://www.youtube.com/watch?v=HIZoGe-CR5Q&feature=related
http://www.youtube.com/watch?v=JG121vFEle4&NR=1&feature=endscreen
1.
2.
3.
4.
Why is it easy to identify synthesis reactions?
What is the product of the synthesis reaction in which sodium combines with oxygen?
Write a balanced chemical equation for the synthesis reaction in which nitrogen reacts with hydrogen.
Complete the following two synthesis reactions by filling in the missing products:
a. 2Al + 3Br2 → ?
b. 2K + S → ?
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Chapter 1. Synthesis Reactions
Review
1. What is a synthesis reaction?
2. Describe the synthesis reaction that produces table salt.
3. Which of the following is a synthesis reaction?
a.
b.
c.
d.
2H2 O → 2H2 + O2
2NO + O2 → 2NO2
2K + 2H2 O → 2KOH + H2
CH4 + 2O2 → CO2 + 2H2 O
References
1. Sodium: Andraž Cerar; Chlorine: Greenhorn1; Salt: cardiae. . Sodium: Used under license from Shutterstock.com; Chlorine: Public Domain; Salt: Used under license from Shutterstock.com
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C HAPTER
2
Decomposition Reactions
• Write the general chemical equation for a decomposition reaction.
• Describe examples of decomposition reactions.
Hydrogen peroxide is a widely used disinfectant for minor cuts and scrapes. You may have a bottle of hydrogen
peroxide like the one pictured here in your medicine cabinet at home. Did you ever notice that hydrogen peroxide
is always kept in a dark brown bottle like this one? Do you know why? The reason is that hydrogen peroxide needs
to be protected from light. If it isn’t, it will gradually break down to water and oxygen. This is a decomposition
reaction.
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Chapter 2. Decomposition Reactions
What Is a Decomposition Reaction?
A decomposition reaction occurs when one reactant breaks down into two or more products. It can be represented
by the general equation:
AB → A + B
In this equation, AB represents the reactant that begins the reaction, and A and B represent the products of the
reaction. The arrow shows the direction in which the reaction occurs.
Q: What is the chemical equation for the decomposition of hydrogen peroxide (H2 O2 ) to water (H2 O) and oxygen
(O2 )?
A: The equation for this decomposition reaction is:
2 H2 O2 → 2 H2 O + O2
Other Examples of Decomposition Reactions
Two more examples of decomposition reactions are described below. You can see additional examples at this URL:
http://www.youtube.com/watch?v=dxlWtsFinTM
• Carbonic acid (H2 CO3 ) is an ingredient in soft drinks. A decomposition reaction takes place when carbonic
acid breaks down to produce water (H2 O) and carbon dioxide (CO2 ). This occurs when you open a can of soft
drink and some of the carbon dioxide fizzes out. The equation for this reaction is:
H2 CO3 → H2 O + CO2
• Another decomposition reaction occurs when water (H2 O) breaks down to produce hydrogen (H2 ) and oxygen
(O2 ) gases (see Figure 2.1). This happens when an electric current passes through the water, as illustrated
below. The equation for this reaction is:
2 H2 O → 2 H2 + O2
Q: What ratio of hydrogen molecules (H2 ) to oxygen molecules (O2 ) is produced in the decomposition of water?
A: Two hydrogen molecules per oxygen molecule are produced because water (H2 O) has a ratio of two hydrogen
atoms to one oxygen atom.
Summary
• A decomposition reaction occurs when one reactant breaks down into two or more products. This can be
represented by the general equation: AB → A + B.
• Examples of decomposition reactions include the breakdown of hydrogen peroxide to water and oxygen, and
the breakdown of water to hydrogen and oxygen.
Vocabulary
• decomposition reaction: Chemical reaction in which one reactant breaks down into two or more products.
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FIGURE 2.1
Decomposition of water
Practice
Watch the video about decomposition reactions at the following URL, and then answer the questions below.
http://www.youtube.com/watch?v=bQJvbmHD1Lg
1. Why are decomposition reactions the opposite of synthesis reactions?
2. What are the products of the decomposition of hydrogen chloride (HCl)?
3. What is missing from each of these balanced equations for decomposition reactions?
a. 2Ni2 O3 → 4Ni + ?
b. 2Al2 O3 → ? + 3O2
4. What is a general rule for the decomposition of metal hydrogen carbonates?
Review
1. What is a decomposition reaction? What is the general equation for a decomposition reaction?
2. Describe the decomposition of hydrogen peroxide, and write a balanced chemical equation for this reaction.
3. Which of the following chemical equations represents a decomposition reaction?
a.
b.
c.
d.
H2 SO3 → H2 O + SO2
2Na + Cl2 → 2NaCl
2K + 2H2 O → 2KOH + H2
NaCl + AgF → NaF + AgCl
References
1. . . CC-BY-NC-SA
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C HAPTER
Chapter 3. Replacement Reactions
3
Replacement Reactions
• Define replacement reaction.
• Contrast single and double replacement reactions.
• Give examples of single and double replacement reactions.
What a job! The man hanging from the burning helicopter in the photo above is a stunt man. He fills in for the
lead actor in the movie in dangerous scenes like this one. Like other stunt workers, he has special training to do
such dangerous work as safely as possible. Replacing actors with stunt workers is common in action movies. Some
chemical reactions also involve replacements. More reactive elements replace less reactive elements in compounds.
These reactions are called replacement reactions.
What Is a Replacement Reaction?
A replacement reaction occurs when elements switch places in compounds. This type of reaction involves ions
(electrically charged versions of atoms) and ionic compounds. These are compounds in which positive ions of a
metal and negative ions of a nonmetal are held together by ionic bonds. Generally, a more reactive element replaces
an element that is less reactive, and the less reactive element is set free from the compound. There are two types of
replacement reactions: single and double. Both types are described below.
Q: Can you predict how single and double replacement reactions differ?
A: One way they differ is that a single replacement reaction involves one reactant compound, whereas a double
replacement reaction involves two reactant compounds. Keep reading to learn more about these two types of
reactions.
Single Replacement Reactions
A single replacement reaction occurs when one element replaces another in a single compound. This type of reaction
has the general equation:
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A + BC → B + AC
In this equation, A represents a more reactive element and BC represents the original compound. During the reaction,
A replaces B, forming the product compound AC and releasing the less reactive element B.
An example of a single replacement reaction occurs when potassium (K) reacts with water (H2 O). A colorless solid
compound named potassium hydroxide (KOH) forms, and hydrogen gas (H2 ) is set free. The equation for the
reaction is:
2K + 2H2 O → 2KOH + H2
In this reaction, which is pictured in the Figure 3.1, a potassium ion replaces one of the hydrogen atoms in each
molecule of water. Potassium is a highly reactive group 1 alkali metal, so its reaction with water is explosive. You
can watch the reaction occurring at this URL: http://simple.wikipedia.org/wiki/Potassium
FIGURE 3.1
Potassium reacting with water.
Q: Find potassium in the periodic table of the elements. What other element might replace hydrogen in water in a
similar replacement reaction?
A: Another group 1 element, such as lithium or sodium, might be involved in a similar replacement reaction with
water.
Double Replacement Reactions
A double replacement reaction occurs when two ionic compounds exchange ions. This produces two new ionic
compounds. A double replacement reaction can be represented by the general equation:
AB + CD → AD + CB
AB and CD are the two reactant compounds, and AD and CB are the two product compounds that result from the
reaction. During the reaction, the ions B and D change places.
Q: Could the product compounds be DA and BC?
A: No, they could not. In an ionic compound, the positive metal ion is always written first, followed by the negative
nonmetal ion. Therefore, A and C must always come first, followed by D or B.
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Chapter 3. Replacement Reactions
An example of a double replacement reaction is sodium chloride (NaCl) reacting with silver fluoride (AgF). This
reaction is represented by the equation:
NaCl + AgF → NaF + AgCl
During the reaction, chloride and fluoride ions change places, so two new compounds are formed in the products:
sodium fluoride (NaF) and silver chloride (AgCl). To better understand how and why double replacement reactions
occur, watch the video at this URL: http://www.brightstorm.com/science/chemistry/chemical-reactions/double-repla
cement-reactions/
Q: When iron sulfide (FeS) and hydrogen chloride (HCl) react together, a double replacement reaction occurs. What
are the products of this reaction? What is the chemical equation for this reaction?
A: The products of the reaction are iron chloride (FeCl2 ) and hydrogen sulfide (H2 S). The chemical equation for this
reaction is:
FeS + 2HCl → H2 S + FeCl2
Summary
• A replacement reaction occurs when elements switch places in compounds. This type of reaction involves
ions. Generally, more reactive elements replace less reactive elements.
• A single replacement reaction occurs when one element replaces another element in one compound. This type
of reaction is represented by: A + BC → B + AC.
• A double replacement reaction occurs when two ionic compounds exchange ions, producing two new ionic
compounds. This type of reaction is represented by: AB + CD → AD + CB.
Vocabulary
• replacement reaction: Chemical reaction in which ions switch places in one compound (single replacement)
or in two compounds (double replacement).
Practice
Examine the double replacement reactions at the following URL. Watch the movies of the reactions, and relate the
molecular diagrams to the slides and still photos. Select one of the reactions, and write a paragraph describing
what occurs during the reaction. Explain how you can tell that a chemical change has occurred, and identify which
compound is the precipitate.
http://www.jce.divched.org/JCESoft/CCA/CCA1/R1MAIN/CD1R2360.HTM
Review
1. What is a replacement reaction?
2. Compare and contrast single and double replacement reactions, and give the general equation for each type of
reaction.
3. Which of the following reactions is not a replacement reaction?
a.
b.
c.
d.
Fe + CuSO4 → FeSO4 + Cu
2Na + 2H2 O → 2NaOH + H2
Zn + 2HCl → ZnCl2 + H2
2Na + Cl2 → 2NaCl
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References
1. Louis Shackleton. . CC-BY-NC-SA
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C HAPTER
Chapter 4. Combustion Reactions
4
Combustion Reactions
• Write the general formula for a combustion reaction.
• Describe examples of combustion reactions.
Don’t try this at home! This performer isn’t really eating fire, but he still puts on an impressive show. You know that
fire is dangerous. It’s hot, it can burn you, and it can easily get out of control. But do you know what fire is? Fire is
the result of a chemical reaction. Whenever something burns, a type of reaction called a combustion reaction occurs.
What Is a Combustion Reaction?
A combustion reaction occurs when a substance reacts quickly with oxygen (O2 ). For example, in the Figure
4.1, charcoal is combining with oxygen. Combustion is commonly called burning, and the substance that burns is
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usually referred to as fuel. The products of a complete combustion reaction include carbon dioxide (CO2 ) and water
vapor (H2 O). The reaction typically gives off heat and light as well. The general equation for a complete combustion
reaction is:
Fuel + O2 → CO2 + H2 O
FIGURE 4.1
The burning of charcoal is a combustion
reaction.
Combustion of Hydrocarbons
The fuel that burns in a combustion reaction contains compounds called hydrocarbons. Hydrocarbons are compounds
that contain only carbon (C) and hydrogen (H). The charcoal pictured above consists of hydrocarbons. So do fossil
fuels such as natural gas. Natural gas is a fuel that is commonly used in home furnaces and gas stoves. The main
component of natural gas is the hydrocarbon called methane (CH4 ). You can see a methane flame in the Figure 4.2.
The combustion of methane is represented by the equation:
CH4 + 2O2 → CO2 + 2H2 O
Q: Sometimes the flame on a gas stove isn’t just blue but has some yellow or orange in it. Why might this occur?
A: If the flame isn’t just blue, the methane isn’t getting enough oxygen to burn completely, leaving some of the
carbon unburned. The flame will also not be as hot as a completely blue flame for the same reason.
You can simulate the combustion of hydrocarbons, including methane, at this URL: http://group.chem.iastate.edu/Gr
eenbowe/sections/projectfolder/flashfiles/stoichiometry/stoic_excess_oxy.html
Summary
• A complete combustion reaction occurs when a fuel reacts quickly with oxygen (O2 ) and produces carbon
dioxide (CO2 ) and water (H2 O). The general equation for a complete combustion reaction is: Fuel + O2 →
CO2 + H2 O
• The fuel that burns in a combustion reaction usually consists of hydrocarbons, which contain only carbon (C)
and hydrogen (H). An example of a hydrocarbon is methane (CH4 ), the main component of natural gas.
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Chapter 4. Combustion Reactions
FIGURE 4.2
The combustion of methane gas heats a
pot on a stove.
Vocabulary
• combustion reaction: Chemical reaction in which a substance reacts quickly with oxygen, producing carbon
dioxide, water, and energy; commonly called burning.
Practice
Watch the video about combustion reactions at the following URL, and then answer the questions below.
http://www.youtube.com/watch?v=oeQTFpuC5Jc&feature=related
1. When does complete combustion occur? What are the products of complete combustion?
2. When does incomplete combustion occur? What are the products of incomplete combustion?
Review
1. What is a combustion reaction?
2. Write the general equation for a combustion reaction.
3. When iron rusts, it slowly combines with oxygen to form iron oxide. Is rusting a combustion reaction?
References
1. Mark H. Anbinder. . CC-BY-NC-SA 2.0
2. Susan van Gelder. . CC-BY-NC-SA 2.0
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C HAPTER
5
Endothermic Reactions
• Define endothermic reaction.
• Describe the role of energy in endothermic reactions.
• Give examples of endothermic reactions.
Did you ever use an instant ice pack like this one? You don’t have to pre-cool it in the freezer. All you need to do is
squeeze the pack and it starts to get cold. How does this happen? The answer is an endothermic chemical reaction.
What Is an Endothermic Reaction
All chemical reactions involve energy. Energy is used to break bonds in reactants, and energy is released when new
bonds form in products. In some chemical reactions, called exothermic reactions, more energy is released when
new bonds form in the products than is needed to break bonds in the reactants. The opposite is true of endothermic
reactions. In an endothermic reaction, it takes more energy to break bonds in the reactants than is released when
new bonds form in the products.
Energy Change in Endothermic Reactions
The word endothermic literally means “taking in heat.” A constant input of energy, often in the form of heat, is
needed to keep an endothermic reaction going. This is illustrated in the Figure 5.1. Energy must be constantly
added because not enough energy is released when the products form to break more bonds in the reactants. The
general equation for an endothermic reaction is:
Reactants + Energy → Products
FIGURE 5.1
Note: ∆H represents the change in energy.
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Chapter 5. Endothermic Reactions
In endothermic reactions, the temperature of the products is typically lower than the temperature of the reactants.
The drop in temperature may be great enough to cause liquids to freeze. That’s what happens in the endothermic
reaction at this URL: http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/chemreac/energychangesrev1.sht
ml
Q: Now can you guess how an instant cold pack works?
A: Squeezing the cold pack breaks an inner bag of water, and the water mixes with a chemical inside the pack. The
chemical and water combine in an endothermic reaction. The energy needed for the reaction to take place comes
from the water, which gets colder as the reaction proceeds.
Photosynthesis
One of the most important series of endothermic reactions is photosynthesis. In photosynthesis, plants make the
simple sugar glucose (C6 H12 O6 ) from carbon dioxide (CO2 ) and water (H2 O). They also release oxygen (O2 ) in the
process. The reactions of photosynthesis are summed up by this chemical equation:
6 CO2 + 6 H2 O → C6 H12 O6 + 6 O2
The energy for photosynthesis comes from light. Without light energy, photosynthesis cannot occur. As you can see
in the Figure 5.2, plants can get the energy they need for photosynthesis from either sunlight or artificial light.
FIGURE 5.2
Summary
• An endothermic reaction is a chemical reaction in which more energy is needed to break bonds in the reactants
than is released when new bonds form in the products.
• A constant input of energy, often in the form of heat, is needed to keep an endothermic reaction going.
• One of the most important series of endothermic reactions is photosynthesis. The energy needed for photosynthesis comes from light.
Vocabulary
• endothermic reaction: Chemical reaction that needs a constant input of energy to continue because it takes
more energy to break bonds in the reactants than is released when new bonds form in the products.
Practice
Watch the series of slides and animations at the following URL. Then compare the energy changes in the reaction of
baking soda with vinegar and the reaction of baking soda solution with calcium chloride.
http://www.inquiryinaction.org/chemistryreview/chemical_change/
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Review
1. What is an endothermic reaction?
2. Why is the temperature of products likely to be lower than the temperature of reactants in an endothermic
reaction?
3. Describe an example of an endothermic reaction.
References
1. Christopher Auyeung. . CC-BY-NC-SA
2. Left: Greg Bishop; Right: Josh Kelahan. . Left: CC-BY-NC-SA 2.0; Right: CC-BY 2.0
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C HAPTER
Chapter 6. Exothermic Reactions
6
Exothermic Reactions
• Define exothermic reaction.
• Describe the role of energy in exothermic reactions.
• Give examples of exothermic reactions.
This mushroom cloud was produced in a 1953 nuclear bomb test in Nevada. There’s no doubt that the explosion
gave off a huge amount of energy. Although not as impressive as nuclear reactions, many chemical reactions also
give off energy. These reactions are called exothermic reactions.
What Is an Exothermic Reaction?
All chemical reactions involve energy. Energy is used to break bonds in reactants, and energy is released when new
bonds form in products. In some chemical reactions, called endothermic reactions, less energy is released when
new bonds form in the products than is needed to break bonds in the reactants. The opposite is true of exothermic
reactions. In an exothermic reaction, it takes less energy to break bonds in the reactants than is released when new
bonds form in the products.
Energy Change in Exothermic Reactions
The word exothermic literally means “turning out heat.” Energy, often in the form of heat, is released as an exothermic reaction proceeds. This is illustrated in the Figure 6.1. The general equation for an exothermic reaction is:
Reactants → Products + Energy
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FIGURE 6.1
Note: ∆H represents the change in energy.
If the energy produced in an exothermic reaction is released as heat, it results in a rise in temperature. As a result,
the products are likely to be warmer than the reactants. That’s what happens in the exothermic reaction at the URL
below. http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/chemreac/energychangesrev1.shtml
Q: You turn on the hot water faucet, and hot water pours out. How does the water get hot? Do you think that an
exothermic reaction might be involved?
A: A hot water heater increases the temperature of water in most homes. Many hot water heaters burn a fuel such as
natural gas. The burning fuel causes the water to get hot because combustion is an exothermic reaction.
Combustion as an Exothermic Reaction
All combustion reactions are exothermic reactions. During a combustion reaction, a substance burns as it combines
with oxygen. When substances burn, they usually give off energy as heat and light. Look at the big bonfire in the
Figure 6.2. The combustion of wood is an exothermic reaction that releases a lot of energy as heat and light. You
can see the light energy the fire is giving off. If you were standing near the fire, you would also feel its heat.
Summary
• An exothermic reaction is a chemical reaction in which less energy is needed to break bonds in the reactants
than is released when new bonds form in the products.
• During an exothermic reaction, energy is constantly given off, often in the form of heat.
• All combustion reactions are exothermic reactions. During combustion, a substance burns as it combines with
oxygen, releasing energy in the form of heat and light.
Vocabulary
• exothermic reaction: Chemical reaction that releases energy because it takes less energy to break bonds in
the reactants than is released when new bonds form in the product.
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Chapter 6. Exothermic Reactions
FIGURE 6.2
Practice
Watch the video about exothermic reactions at the following URL, and then answer the questions below. http://w
ww.videojug.com/film/a-guide-to-exothermic-reactions
1. Why do exothermic reactions heat up?
2. Explain why this reaction is exothermic: CH4 + F2 → CH3 F + HF.
Review
1. What is an exothermic reaction?
2. Why are the products of an exothermic reaction likely to be warmer than the reactants?
3. Describe an example of an exothermic reaction.
References
1. Christopher Auyeung. . CC-BY-NC-SA
2. Thaddeaus. . Public Domain
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C HAPTER
7
Conservation of Energy in
Chemical Reactions
• Summarize the role of energy in chemical reactions.
• State the law of conservation of energy.
• Explain how energy is conserved in chemical reactions.
The blue flame in this photo is burning inside a home furnace. The fuel is natural gas, and it combines with oxygen
when it burns. This chemical reaction, called a combustion reaction, gives off a lot of energy.
Energy and Chemical Reactions
All chemical reactions involve energy. Energy is used to break bonds in reactants, and energy is released when new
bonds form in products. Like the combustion reaction in a furnace, some chemical reactions require less energy to
break bonds in reactants than is released when bonds form in products. These reactions, called exothermic reactions,
release energy. In other chemical reactions, it takes more energy to break bonds in reactants than is released when
bonds form in products. These reactions, called endothermic reactions, absorb energy.
Conservation of Energy
Whether a chemical reaction absorbs or releases energy, there is no overall change in the amount of energy during
the reaction. That’s because energy cannot be created or destroyed. This is the law of conservation of energy.
Energy may change form during a chemical reactionexample, from chemical energy to heat energy when gas burns
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Chapter 7. Conservation of Energy in Chemical Reactions
in a furnacethe same amount of energy remains after the reaction as before. This is true of all chemical reactions.
You can learn more about the law of conservation of energy at this URL: http://www.fi.edu/guide/hughes/energycon
servation.html
Q: If energy can’t be destroyed during a chemical reaction, what happens to the energy that is absorbed in an
endothermic reaction?
A: The energy is stored in the bonds of the products as chemical energy. In an endothermic reaction, the products
have more stored chemical energy than the reactants. This is represented by the graph on the left in the Figure 7.1.
In an exothermic reaction, the opposite is true. The products have less stored chemical energy than the reactants.
You can see this in the graph on the right in the Figure 7.1.
FIGURE 7.1
Note: ∆H represents the change in energy.
Q: What happens to the excess energy in the reactants of an exothermic reaction?
A: The excess energy is generally released to the surroundings when the reaction occurs. In a home heating system,
for example, the energy that is released during combustion in the furnace is used to heat the home.
Summary
• All chemical reactions involve energy. Energy is used to break bonds in reactants, and energy is released when
new bonds form in products. Endothermic reactions absorb energy, and exothermic reactions release energy.
• The law of conservation of energy states that matter cannot be created or destroyed. Whether a chemical
reaction absorbs or releases energy, there is no overall change in the amount of energy during the reaction.
Vocabulary
• law of conservation of energy: Law stating that energy cannot be created or destroyed in chemical reactions
or energy conversions.
Practice
Go through the tutorial at the following URL, and then answer the questions at the end. http://www.wisc-online.c
om/objects/ViewObject.aspx?ID=GCH8705
Review
1. Summarize the role of energy in chemical reactions.
2. What is the law of conservation of energy?
3. Explain how energy is conserved in an endothermic reaction.
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References
1. Christopher Auyeung. . CC-BY-NC-SA
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