Lesson 11 Classifying Chemical Reactions
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| Course: | Science 10 [5 cr] - AB Ed copy 1 |
| Book: | Lesson 11 Classifying Chemical Reactions |
| Printed by: | Guest user |
| Date: | Sunday, 7 September 2025, 11:11 PM |
Introduction
Did you know that there are different types of chemical reactions?
B11.1 two students writing equations
Using and analyzing chemical reactions is a fundamental skill for any chemist. The first step in this process is the ability to classify the chemical reaction types. The five main reaction types you will be studying are formation, decomposition,
single replacement, double replacement, and hydrocarbon combustion. As with most chemistry concepts, recognizing patterns is the first step to understanding a concept.
In this lesson, you will learn how to classify the five most common reaction types.
In this lesson, you will learn how to classify the five most common reaction types.
Targets
By the end of this lesson, you will be able to
-
classify and identify categories of chemical reactions, including formation, decomposition, hydrocarbon combustion, single replacement, and double replacement
Watch This
Beautiful Chemical Reactions @ YouTube Beauty of Science
This video will introduce you to chemical reactions by giving you a close up view of the changes. This will help get you in the right mindset for this lesson.
Classifying Chemical Reactions
By learning how to classify reactions, you will begin to recognize patterns that will make it easier to write chemical reaction equations.
B11.2 Examples of chemical reactions
The ability to classify reactions will give you the foundational skills needed to balance chemical reaction equations. As well, it is a stepping stone to predict products for chemical reactions when given the identity of the reactants.
You will be responsible for classifying five common types of reactions: formation, decomposition, single replacement, double replacement, and hydrocarbon combustion.
You will be responsible for classifying five common types of reactions: formation, decomposition, single replacement, double replacement, and hydrocarbon combustion.
Simple formation reactions have elements reacting to produce one product.
For example, the formation of table salt from its constituent elements:
2Na(s) + Cl2(g) → 2NaCl(s)
A generalized model can be written as
A + B → AB
Or an alternate model is
Examples of more complex formation reactions can include one or more compounds reacting to form a single product, such as
2NO(g) + O2(g) → 2NO2(g)
Element + Element → Compound
For example, the formation of table salt from its constituent elements:
2Na(s) + Cl2(g) → 2NaCl(s)
A generalized model can be written as
A + B → AB
Or an alternate model is
Examples of more complex formation reactions can include one or more compounds reacting to form a single product, such as
2NO(g) + O2(g) → 2NO2(g)
This reaction has one reactant—a compound—that is broken down into elements.
For example, the decomposition of water into its constituent elements:
2H2O(l) → 2H2(g) + O 2(g)
A generalized model can be written as
AB → A + B
Or an alternate model is
Examples of more complex decomposition reactions can include one or more compounds being produced from a single reactant, such as
CaCO3(s) → CaO(s) + CO2(g)
Compound → Element + Element
For example, the decomposition of water into its constituent elements:
2H2O(l) → 2H2(g) + O 2(g)
A generalized model can be written as
AB → A + B
Or an alternate model is
Examples of more complex decomposition reactions can include one or more compounds being produced from a single reactant, such as
CaCO3(s) → CaO(s) + CO2(g)
This reaction has an element reacting with a compound. During the reaction, the commonly charged ions (the two positive ions or the two negative ions) swap out to produce a new element and a new compound.
For example, the reaction of copper metal with silver nitrate solution, as shown below. In this reaction, the two metal atoms swap places.
Cu(s) + 2AgNO3(aq) → 2Ag(s) + Cu(NO3)2(aq)
A generalized model can be written as
A + BC → B + AC
Or an alternate model is
Element + Compound → Element + Compound
For example, the reaction of copper metal with silver nitrate solution, as shown below. In this reaction, the two metal atoms swap places.
Cu(s) + 2AgNO3(aq) → 2Ag(s) + Cu(NO3)2(aq)
A generalized model can be written as
A + BC → B + AC
Or an alternate model is
This reaction has two compounds reacting to produce two new compounds.
Neutralization reactions are usually examples of double replacement.
HCl(aq) + NaOH(aq) → NaCl(aq) + HOH(l)
And usually precipitation reactions are examples of these as well.
Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq)
A generalized model can be written as
AB + CD → AD + CB
Or an alternate model is
Compound + Compound → Compound + Compound
Neutralization reactions are usually examples of double replacement.
HCl(aq) + NaOH(aq) → NaCl(aq) + HOH(l)
And usually precipitation reactions are examples of these as well.
Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq)
A generalized model can be written as
AB + CD → AD + CB
Or an alternate model is
Did You Know?
B11.3 water molecule
The chemical formula for water can be written as H2O(l) or HOH(l). When balancing a single replacement or double replacement reaction, it can be easier to write the chemical formula as HOH; that way, you can balance the hydroxide and the hydrogen as separate entities. You will learn more about this in Lesson 12.
You should recall from previous science courses that a fire triangle needs fuel, oxygen, and a source of ignition. In a hydrocarbon combustion reaction, a hydrocarbon—a compound composed of the elements hydrogen and carbon—reacts with oxygen
to produce carbon dioxide and water. The water produced is usually a vapour.
For example, the combustion of propane (C3H8(g)) in a barbeque:
C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g)
A generalized model can be written as
One key to being able to classify reactions is it to identify the reactants and products as elements or compounds. You also need to recognize that a hydrocarbon combustion reaction will always produce carbon dioxide and water vapour.
For example, the combustion of propane (C3H8(g)) in a barbeque:
C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g)
A generalized model can be written as
CxHy(g) + O2(g) → CO2(g) + H2O(g)
hydrocarbon + oxygen → carbon dioxide + water
hydrocarbon + oxygen → carbon dioxide + water
One key to being able to classify reactions is it to identify the reactants and products as elements or compounds. You also need to recognize that a hydrocarbon combustion reaction will always produce carbon dioxide and water vapour.
Did You Know?
B11.4 Carbon monoxide detector
If there is a lack of oxygen when a hydrocarbon is undergoing combustion, deadly carbon monoxide can be produced in addition to carbon dioxide. Many homes are now equipped with CO detectors.
Examples
Classify each of the following chemical reaction equations as formation, simple decomposition, hydrocarbon combustion, single replacement, or double replacement. Each example has a video to go with it. To play the video, click on the play icon next to the example.
Compound + Element → Compound + Element
This is a single replacement reaction. https://adlc.wistia.com/medias/7ldgb8ls6k
This is a single replacement reaction. https://adlc.wistia.com/medias/7ldgb8ls6k
Hydrocarbon + Oxygen → Carbon Dioxide + Water Vapour
This is a hydrocarbon combustion reaction. https://adlc.wistia.com/medias/ajkz8uyoyj
This is a hydrocarbon combustion reaction. https://adlc.wistia.com/medias/ajkz8uyoyj
Compound → Element + Element
This is a simple decomposition reaction. https://adlc.wistia.com/medias/084w9fzczt
This is a simple decomposition reaction. https://adlc.wistia.com/medias/084w9fzczt
Compound + Compound → Compound + Compound
This is a double replacement reaction. https://adlc.wistia.com/medias/am2hbujy31
This is a double replacement reaction. https://adlc.wistia.com/medias/am2hbujy31
Element + Element → Compound
This is a formation reaction. https://adlc.wistia.com/medias/eqd4t1xuoo
This is a formation reaction. https://adlc.wistia.com/medias/eqd4t1xuoo
Read This
Please read pages 91 to 101 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on recognizing and classifying types
of chemical reactions. Remember, if you have any questions or you do not understand something, ask your teacher! Practice Questions
Complete the following practice question to check your understanding of the concept you just learned. Make sure you write a complete answer to the practice
question in your notes. After you have checked your answer, make corrections to your response (where necessary) to study from.-
Classify each of the following chemical reaction equations as formation, decomposition, hydrocarbon combustion, single replacement, or double replacement.
- P4(s) + 5O2(g) → P4O10(g)
Element + Element → Compound
This is a formation reaction. - 2Na(s) + 2H2O(l)→ H2(g) + 2NaOH(aq)
Element + Compound → Element + Compound
This is a single replacement reaction. - CH4(l) + 2O2(g) → CO2(g) + 2H2O(g)
Hydrocarbon + Oxygen → Carbon Dioxide + Water
This is a hydrocarbon combustion reaction. - 2AgCl(s) → 2Ag(s) + Cl2(g)
Compound → Element + Element
This is a simple decomposition reaction. - H2SO4(aq) + KOH(aq) → K2SO4(aq) + HOH(l)
Compound + Compound → Compound + Compound
This is a double replacement reaction.
- P4(s) + 5O2(g) → P4O10(g)
- Classify each of the following diagrams as representing a formation, decomposition, single replacement, or double replacement chemical reaction.
a.
double replacementb.
decomposition
c.
formation
d.
single replacement
Information Displayed in a Chemical Reaction Equation
What information is included in a chemical reaction equation?
B11.5 Writing out a chemical reaction equation
Chemical reaction equations display a lot of information. Understanding how to interpret that information is key to your success in this section.
Entities (elements and compounds) that are written on the left-hand side of the arrow are the reactants; these are what you start with in a chemical reaction.
Entities written on the right-hand side of the arrow are the products; these are what you end up with once the reaction goes to completion.
Numbers in front of formulas are coefficients, and these are used to balance the reaction. This is to ensure that there are the same number of atoms of each type of element on the reactant side and the product side.
Entities (elements and compounds) that are written on the left-hand side of the arrow are the reactants; these are what you start with in a chemical reaction.
Entities written on the right-hand side of the arrow are the products; these are what you end up with once the reaction goes to completion.
Numbers in front of formulas are coefficients, and these are used to balance the reaction. This is to ensure that there are the same number of atoms of each type of element on the reactant side and the product side.
States are indicated in brackets behind each entity’s formula. Please note that since your textbook was written, standards have changed and states are no longer written as subscripts. The states used are
(s)—solid
(l)—liquid
(g)—gas
(aq)—aqueous
Aqueous means a solution; the indicated compound has been dissolved in water to produce a solution.
Read This
Please read pages 86 to 88 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on how to properly write chemical reaction
equations. Remember, if you have any questions or you do not understand something, ask your teacher! Practice Questions
Complete the following practice question to check your understanding of the concept you just learned. Make sure you write a complete answer to the practice
question in your notes. After you have checked your answer, make corrections to your response (where necessary) to study from.- List four pieces of information provided by a balanced chemical reaction equation.
A balanced chemical reaction equation provides
- the formulas of the reactants
- the formulas of the products
- the states of the reactants and products
- the number of molecules of the reactants and products
- Use the following chemical reaction equation to explain the following terms: reactants, products, state, and coefficient.
2KClO3(s) → 2KCl(s) + 3O2(g)
reactant—KClO3(s)
products—KCl(s) and O2(g)
states—KCl and KClO3 are both solids (s) and O2 is a gas (g)
coefficients—KCl and KClO3 both have a 2 as the coefficient, whereas O2 has a 3
Types of Chemical Reaction Equations
What are the three different ways that chemical reactions can be written?
B11.6 Chemical reaction equation
Most often, you will use balanced chemical reaction equations. On occasion, other types of chemical reaction equations—word equations and skeleton equations—will be used. Each type of reaction equation conveys slightly different information.
A word equation is a way of organizing and displaying information about a chemical change. It is a gateway to eventually writing a balanced chemical reaction equation.
For example, a piece of zinc metal is dropped into a beaker of hydrobromic acid to produce aqueous zinc bromide and bubbles of hydrogen gas.
Reactants are the entities that are used to start the chemical reaction. They are separated by a plus sign. An arrow is used to separate the reactants from the products. A key term in this example is “to produce,” which indicates which entities are the products.
zinc + hydrobromic acid → zinc bromide + hydrogen
The reactants—zinc and hydrobromic acid—could have been written in any order and still be correct. The same goes for the products.
For example, a piece of zinc metal is dropped into a beaker of hydrobromic acid to produce aqueous zinc bromide and bubbles of hydrogen gas.
Reactants are the entities that are used to start the chemical reaction. They are separated by a plus sign. An arrow is used to separate the reactants from the products. A key term in this example is “to produce,” which indicates which entities are the products.
zinc + hydrobromic acid → zinc bromide + hydrogen
The reactants—zinc and hydrobromic acid—could have been written in any order and still be correct. The same goes for the products.
A skeleton equation shows the formulas of the reactants and products, but it does not show the correct proportions of either—no coefficients are added into a skeleton equation. You will need to recall the guidelines for writing chemical formulas from Section 2.
For the example above, the skeleton equation is
Zn(s) + HBr(aq) → ZnBr2(aq) + H2(g)
For the example above, the skeleton equation is
Zn(s) + HBr(aq) → ZnBr2(aq) + H2(g)
B11.7 Chemical reaction
B11.8 Balancing
Recall from previous science courses that the law of conservations of mass states that the total mass of reactants must equal the total mass of products. This law is used to balance chemical reaction equations by ensuring the number of atoms of each element is the same on the reactant side and the product side. You will learn how to balance chemical reaction equations in the next lesson. The balanced equation for the above example would be
Zn(s) + 2HBr(aq) → ZnBr2(aq) + H2(g)
Zn(s) + 2HBr(aq) → ZnBr2(aq) + H2(g)
Read This
Please read pages 86 to 88 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on the three ways that chemical reaction information can be displayed. Remember, if you have any questions or you do not understand something, ask your teacher! Practice Questions
Complete the following practice question to check your understanding of the concept you just learned. Make sure you write a complete answer to the practice
question in your notes. After you have checked your answer, make corrections to your response (where necessary) to study from.- When a solid strip of magnesium is ignited, it reacts with oxygen gas from the air to produce solid magnesium oxide. Write the word equation and a skeleton equation for the described reaction.
Word equation:
magnesium + oxygen → magnesium oxide
Skeleton equation:
Mg(s) + O2(g) → MgO(s)
- Aqueous solutions of barium chloride and potassium hydroxide react to produce solid barium hydroxide and aqueous potassium chloride. Write the word equation and a skeleton equation for the described reaction.
Word equation:
barium chloride + potassium hydroxide → barium hydroxide + potassium chloride
Skeleton equation:
BaCl2(aq) + KOH(aq) → Ba(OH)2(s) + KCl(aq)
Conclusion
Classifying chemical reaction types is the first step toward the ability to predict products from given reactants.
B11.9 Writing a chemical formula
This lesson looked at analyzing reactants and products to determine the type of chemical reaction. You learned about the five common reaction types: formation, decomposition, single replacement, double replacement, and hydrocarbon combustion. You also learned what information is displayed in a balanced chemical reaction equation.
In the next lesson, you will learn how to balance chemical reaction equations and, given the reactants, predict what products will be produced.
In the next lesson, you will learn how to balance chemical reaction equations and, given the reactants, predict what products will be produced.
Watch This
Classifying Types of Chemical Reactions Practice Problems @ YouTube Tyler DeWitt
Watch this video as a review of how to classify chemical reaction types. Please note that formation reactions are referred to as synthesis reactions.
2.6 Assignment
Unit 2 Assignment Lessons 10-13
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Online Questions
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