CR_Synthesis Reactions Lesson

Synthesis Reactions

Now that you are familiar with the five basic types of chemical reactions (synthesis, decomposition, single displacement, double displacement, and combustion), you are ready to go a little bit deeper. Identifying a reaction as a particular type isn't too hard. But, in order to predict the specific products of any of those reactions, you need some more information. Let's begin with types of synthesis reactions.  

Types of Synthesis Reactions

1. Direct combination of two elements will produce a binary compound or molecule. Recall that binary simply means that it is made of two types of elements. This one is best represented by the generic equation we used before.

A+B AB Examples: 2K+ Cl2 2KCI (Remember that chlorine is diatomic.) C(s) + O2(g) → CO2(g) (This could also be classified as combustion.)

Sometimes you will see this type of reaction stated more specifically as these two reactions:

LaTeX: \color{blue}\text{Metal + Oxygen}\longrightarrow \text{Metal Oxide} \\ \color{blue}\text{Nonmetal + Oxygen}\longrightarrow \text{Nonmetal Oxide} \\Metal + Oxygen⟶Metal OxideNonmetal + Oxygen⟶Nonmetal Oxide

Don't let these confuse you. They are still just direct combinations of two elements. There are often many ways to describe the same thing in chemistry.   So, don't be fooled by specific wordings. You should be able to recognize that both of these reactions fit in to the direct combination of elements reaction type.

2. Metallic oxides and carbon dioxide react to produce metallic carbonates. Recall that carbonate is CO3-2.   A generic form of this reaction is:

MO + CO2 MCO 3 (M represents any metal. You would need to apply charge of that metal when writing the formula.) Example: CaO + CO2 → CaCO3

3. Binary chlorides and oxygen react to produce a chlorate. A binary chloride simply means an element combined with chlorine. Recall that chlorate is ClO3-1. A generic form of this reaction is:

XCI + O2 →XCIO3 (X represents any element. You would need to apply charge of that metal when writing the formula.) Example: KCI + O2 → KCIO 3

4. Metal oxide plus water yields an ionic base. An ionic base is a metal combined with hydroxide (OH-). A generic form of this reaction is:

MO+ H2O → MOH (M represents a metal. You would need to apply charge of that metal when writing the formulas.) Examples: MgO (s) + H2O(1) Na2O+ H2O → Mg(OH)2(s) NaOH

5. A non-metal oxide plus water yields an acid. You will learn more about acids on later pages in this unit. For now, you just need to recognize acids as compounds that begin with a hydrogen ion (HCl, H2SO4, etc.). A generic form of this reaction is:

(NM)O + H2O → acid (NM represents a non-metal. You would need to apply charge of that non-metal when writing the formulas.) Examples: CO2(g) + H2O(l) → H2CO3(aq) N2O5+ H2O→ HNO3 How do you know which specific acid forms? The acid that is formed has no change in the oxidation number of the nonmetal. You will learn about oxidation numbers later in this unit. For now, just add up all the numbers of each element on the reactant side following the examples below. In the first example, CO2(g) + H2O) contains 1 carbon, 3 oxygen, 2 hydrogen. Put these all together, starting with the H, ending with O to get: H2CO3 In the second example, N2O5+ H2O contains 2 nitrogen, 6 oxygen, 2 hydrogen. Put these all together, starting with the H, ending with O to get: H2N2O6 This one can be simplified to 2HNO3

Now, let's mix these up. First, determine where each reaction fits into the categories above. Then, apply that rule to determine the product. You may find it easier to write out the formulas of the reactants before you determine which rule to apply.

Examples: 1) Lithium chloride combines with oxygen gas. Begin by writing out the correct formulas for each reactant: LiCl + 02 → Now, determine the type of synthesis reaction from the list above: This is a binary chloride reacting with oxygen. This produces a chlorate. Write the product and balance: 2LiCl + 302 2LICIO3 LiClO2 LiClO3 + 2) Sodium oxide combines with carbon dioxide. Begin by writing out the correct formulas for each reactant: Na2O + CO2 → Now, determine the type of synthesis reaction from the list above: A metal oxide and carbon dioxide combine to form a carbonate. Write the product and balance: Na2O + CO2 Na2CO3

Remember to work on the module practice problems as you complete each section of content.

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