1. 11.2 Types of Chemical Reactions
Read the lesson title aloud to students.

2. Types of Chemical Reactions
The 5 main types of chemical reactions are;
Combination reaction
Decomposition reaction
Single-replacement reaction
Double-replacement reaction
Combustion reaction
Review the five main types of chemical reactions.
Tell students to recall what they know about the terms combination, decomposition, replacement, and combustion as they learn about these types of chemical reactions.
Hand out student worksheets and encourage students to complete them as they work through the lesson.

3. Combination Reactions
In a combination reaction, two or more reactants combine to form a single product. Combination reactions are also called synthesis reactions.
Ask students to review what the word combine means. Explain that in a combination reaction, two or more reactants combine to form a single product.
Click to reveal the magnesium and oxygen reaction.
Ask a student to identify the reactants in the equation.
Click to highlight the reactants.
Ask: How many reactants are there?
Answer: two
Ask a student to identify the product in the reaction.
Click to highlight the product.
Ask: How many products are there?
Answer: one
Ask: Is this a combination reaction?
Answer: Yes.
2Mg(s) + O2(g)
2MgO(s) 

4. Decomposition Reactions
In a decomposition reaction, one reactant breaks down to form two or more products.
Tell students that the root word of decomposition is decompose. Ask them to describe the biological sense of the word decompose. Then have volunteers brainstorm ways that a decomposition reaction accurately describes what is occurring to the reactant during this kind of reaction.
Ask: What does the second photograph represent?
Answer: the addition of heat to start the reaction
Ask: Why do the mercury and oxygen atoms change sizes between the reactant and the products?
Answer: Mercury cations are smaller than mercury atoms. Oxygen anions are larger than oxygen atoms.
Ask: How can we tell the difference between a combination reaction and a decomposition reaction?
Answer: A combination reaction forms one product from two or more substances, and a decomposition reaction forms two or more products from a single reactant.
Emphasize to students that decomposition reactions consist of one substance forming two or more different substances. Students tend to limit decomposition reactions to the decomposition of a compound into its component elements. Explain that a compound can also break down into an element and a compound or into two or more compounds.
2HgO(s)
2Hg(l) + O2(g) 

5. Single-Replacement Reactions
In a single-replacement reaction, an element reacts with a compound to form a different compound and a different element. One of the elements in the compound is replaced by something else.
Review the definition of a single-replacement reaction with students. Point out that in the reaction shown, potassium atoms replace hydrogen atoms in water to form KOH. If necessary, rewrite water as HOH to help students see the relationship to KOH.
Point out to students that it is often helpful to use analogies to better understand vocabulary terms. Brainstorm analogies for single-replacement reaction, such as substituting a player on a basketball team, substituting an item in a restaurant, or putting a spare tire on a car.
Explain that single-replacement reactions can be compared to people switching places. Ask for three volunteers to demonstrate this concept in front of the class. Have two people stand next to each other. The third person approaches and replaces one of the others. Point out that in a chemical reaction, only certain substances can replace other substances in a given compound.
2K(s) + H2O(l)
2KOH(aq) + H2(g) 

6. Activity Series
An activity series describes the relative reactivities of different elements. The higher an element is on the chart, the more reactive it is.
An element can only replace elements in a compound that are below it on the table.
Explain that in single-replacement reactions, only certain substances can replace other substances in a given compound. Review the table with students. Explain that the table shows which metals can replace another metal in a given compound.
Explain that elements higher up in the activity series table can replace those lower down, but lower elements cannot replace higher elements.
Ask: If magnesium oxide is mixed with lead, will a reaction occur?
Answer: No.
Ask: What is a metal that would replace magnesium in magnesium oxide?
Answer: lithium, potassium, calcium, or sodium

7. Double-Replacement Reactions
In a double-replacement reaction, two ionic compounds react to form two new ionic compounds. They “change partners” with the other compound.
Review the definition of a single-replacement reaction with students. Ask students to discuss whether a double replacement means that two parts are being swapped or if it means that a replacement is made and then reversed to produce the original again. Ask volunteers to act out the difference between these two processes to help in the discussion.
Click to highlight the lead compounds in the reactants and products.
Ask: With what ion is the lead bonded in the reactants?
Answer: nitrate
Ask: With what ion is the lead bonded in the products?
Answer: iodide
Click to highlight the potassium compounds in the reactants and products.
Ask: With what ion is the potassium bonded in the reactants?
Ask: With what ion is the potassium bonded in the products?
Point out that the nitrate and iodide ions have “switched” places.
Explain to students that the smaller circles are molecular views of what is present in each beaker.
Ask: What does the presence of water molecules indicate about a compound?
Answer: The compound is in aqueous solution.
Ask: What characteristic do KI and Pb(NO3)2 share?
Answer: They are both ionic compounds.
Explain to students that a double-replacement reaction always involves two ionic compounds in aqueous solution. In addition, one of the products often is either a solid or a gas.
Ask: What happens to a solid or gas that forms in aqueous solution?
Answer: A solid will precipitate and a gas will bubble out of solution.
Ask: Is one of the products in this reaction a solid or a gas? Why?
Answer: Yes; PbI2 is an insoluble compound, so it will precipitate from solution when it forms.
2KI(aq) + Pb(NO3)2(aq)
PbI(s) + 2KNO3(aq) 

8. Combustion Reactions 
In a combustion reaction, a substance reacts with oxygen. A complete combustion reaction of a hydrocarbon will produce water, carbon dioxide, heat, & light.
Point out to students that the verb combust means “to catch fire.”
Ask: What kind of substances combust?
Answer: substances that can react readily with oxygen
Ask: How might substances literally appear to “catch fire”?
Sample answer: Oxygen is an invisible gas, so flames appear on the substance as if they came from nowhere.
Explain to students that the term combustion was used long before scientists understood how combustion works.
Remind them that the complete combustion of a hydrocarbon, such as methane, always produces water, carbon dioxide, heat, and light.
Ask: Do all combustion reactions involve hydrocarbons?
Answer: No.
Ask: Do all combustion reactions produce flames?
CH4(g) + 2O2(g)
CO2(g) + 2H2O(g) 