CHAPTER 12 Chemical Reactions and Equations
CHAPTER 12 LESSON 2
Key Concepts
? How can you recognize the type of chemical reaction by the number or type of reactants and products?
? What are the different types of chemical reactions?
Chemical Reactions and Equations
Types of Chemical Reactions
What do you think? Read the two statements below and decide
whether you agree or disagree with them. Place an A in the Before column if you agree with the statement or a D if you disagree. After you've read this lesson, reread the statements to see if you have changed your mind.
Before
Statement
After
3. Reactions always start with two or more substances that react with each other.
4. Water can be broken down into simpler substances.
Copyright ? McGraw-Hill Education.
Sticky Notes As you read, use sticky notes to mark information that you do not understand. Read the text carefully a second time. If you still need help, write a list of questions to ask your teacher.
Make a four-door book to organize your notes about the different types of chemical reactions.
Patterns in Reactions
If you have ever used hydrogen peroxide, you might have noticed that it comes in a dark bottle. This is because light causes hydrogen peroxide to change into other substances. You might have seen video of an old building or a sports facility being demolished by an explosion. How is the reaction between hydrogen and light similar to a building being demolished? In both, one reactant breaks down into two or more products.
The breakdown of one reactant into two or more products is one of four major types of chemical reaction. Each type of chemical reaction follows a unique pattern in the way atoms in reactants rearrange to form products. In this lesson, you will read how chemical reactions are classified by recognizing patterns in the way the atoms recombine.
Types of Chemical Reactions
Many different types of reactions can occur. It would be impossible to memorize them all. However, most chemical reactions fit into four major categories. Understanding these categories of reactions can help you predict how compounds will react and what products will form.
370 Chemical Reactions and Equations
Types of Chemical Reactions
Synthesis
A synthesis (SIHN thuh sus) is a type of chemical reaction in which two or more substances combine and form one compound. In the synthesis reaction on the left below, magnesium (Mg) reacts with oxygen (O2) in the air and forms magnesium oxide (MgO). You can recognize a synthesis reaction because two or more reactants form only one product.
Visual Check
1. Identify How many
products result from a synthesis reaction?
Synthesis and Decomposition Reactions
Synthesis Reactions
Decomposition Reactions
2Mg + O2 2MgO
2H2O2
magnesium oxygen magnesium oxide hydrogen peroxide
2H2O + O2
water
oxygen
Decomposition
In a decomposition reaction, one compound breaks down and forms two or more substances. You can recognize a decomposition reaction because one reactant forms two or more products. For example, hydrogen peroxide (H2O2), shown on the right above, decomposes and forms water (H2O) and oxygen gas (O2). Notice that decomposition is the reverse of synthesis.
Replacement
In a replacement reaction, an atom or a group of atoms replaces part of a compound. Two types of replacement reactions can occur. The figure below describes both types.
In a single-replacement reaction, one element replaces another element in a compound. In this type of reaction, an element and a compound react and form a different element and a different compound. In a double-replacement reaction, the negative ions in two compounds switch places, forming two new compounds. In this type of reaction, two compounds react and form two new compounds.
Key Concept Check 2. Recognize How can you tell the difference between synthesis and decomposition reactions?
Visual Check 3. Interpret In the singlereplacement equation, which elements switched places?
Replacement Reactions
Single Replacement
Double Replacement
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2AgNO3 + Cu Cu(NO3)2 + 2Ag
silver nitrate copper copper nitrate silver
Types of Chemical Reactions
Pb(NO3)2 + 2KI 2KNO3 + PbI2
lead potassium potassium lead
nitrate iodide
nitrate iodide
Chemical Reactions and Equations 371
Key Concept Check 4. Summarize What are the different types of chemical reactions?
Visual Check 5. Identify Which element is common to all combustion reactions?
Combustion
Combustion is a chemical reaction in which a substance combines with oxygen and releases energy. A combustion reaction usually releases energy as thermal energy and light energy. For example, burning is a common combustion reaction. The burning of fossil fuels produces the energy we use to cook food, power vehicles, and light cities.
The equation in the figure below describes the burning of the fossil fuel propane (C3H8). Combustion reactions always contain oxygen (O2) as a reactant. These reactions often produce carbon dioxide (CO2) and water (H2O).
Combustion Reactions
substance +
O2
C3H8 propane
+
5O2
oxygen
substance(s)
3CO2 + 4H2O carbon water dioxide
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372 Chemical Reactions and Equations
Types of Chemical Reactions
Mini Glossary
combustion: a chemical reaction in which a substance combines with oxygen and releases energy
single replacement: a type of chemical reaction in which one element replaces another element in a compound
decomposition: a type of chemical reaction in which one compound breaks down and forms two or more substances
synthesis (SIHN thuh sus): a type of chemical reaction in which two or more substances combine and form one compound
double replacement: a type of chemical reaction in which the negative ions in two compounds switch places, forming two new compounds
1. Review the terms and their definitions in the Mini Glossary. Write a sentence that identifies the types of energy that combustion usually releases.
2. Identify each type of chemical reaction described in the diagram.
Type: substance + O2
substance(s)
Type:
A + B
AB
Types of Chemical Reactions
Type: AB
A + B
Type:
Replacement
An atom or a group of atoms replaces part of a compound.
Type: An element and a compound form a different element and compound.
What do you think
Reread the statements at the beginning of the lesson. Fill in the After column with an A if you agree with the statement or a D if you disagree. Did you change your mind?
Types of Chemical Reactions
Type:
Two compounds form two new compounds.
Log on to ConnectED.mcgraw- and access your textbook to find this lesson's resources.
END OF LESSON
Chemical Reactions and Equations 373
Copyright ? McGraw-Hill Education.
Lesson 2 Types of Chemical Reactions
Predict three facts that will be discussed in Lesson 2 after reading the headings. Write your facts in your Science Journal.
Patterns in Reactions
I found this on page .
Types of Chemical Reactions
I found this on page .
Generalize the concept of patterns in chemical reactions.
Number of types:
Major Types of Chemical Reactions
Determined by:
Describe and model synthesis and decomposition reactions. First, describe the reactions. Then draw simple shapes to model how substances behave during these reactions.
Synthesis
Decomposition
Explanation
Diagram
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374 Chemical Reactions and Equations
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