Types of Reactions Key Terms: Combustion reaction Decomposition reaction Double Replacement reaction Hydrocarbon Single replacement Reaction Synthesis

Lesson Objectives The student will: describe what is occurring in synthesis, decomposition, single replacement, double replacement, and combustion reactions. classify a chemical reaction as a synthesis, decomposition, single replacement, double replacement, or a combustion reaction. predict the products of simple reactions.

Vocabulary combustion reaction decomposition reaction a reaction in which oxygen reacts with another substance to produce carbon dioxide and water decomposition reaction a reaction in which one reactant breaks down to form two or more products double replacement reaction a reaction in which two reactants form products by having the cations exchange places hydrocarbon an organic substance consisting of only hydrogen and carbon single replacement reaction a reaction in which an element reacts with a compound to form products synthesis reaction a reaction in which two or more reactants combine to make one product

Introduction Chemical reactions are classified into types to help us analyze them and to help us predict what the products of the reaction will be. The five major types of chemical reactions are synthesis, decomposition, single replacement, double replacement, and combustion.

Synthesis Reactions A synthesis reaction is one in which two or more reactants combine to make one product A + B  AB Synthesis reactions occur as a result of two or more simpler elements or molecules combining to form a more complex molecule. We can always identify a synthesis reaction because there is only one product

Synthesis Examples Lets take hydrogen and oxygen to form water 2 H2(g) + O2(g)  2 H2O(l) Lets take sodium and chlorine to make table salt 2 Na(s) + Cl2(g) 2 NaCl(s)

Sample Problem 1 Write the chemical equation for the synthesis reaction of silver bromide, AgBr 2 Ag(s) + Br2(l)  2 AgBr(s) Predict the products for the following reaction: CO2(g) + H2O(l) (Hint- a CO3 ion forms) H2CO3(aq)

Decomposition Reactions When one type of reactant breaks down to form two or more products, we have a decomposition reaction. The best way to remember a decomposition reaction is that for all reactions of this type, there is only one reactant. The general equation for a decomposition reaction is: AB  A + B

Decomposition Examples Look at the equation below for an example of a decomposition reaction. In this reaction, ammonium nitrate breaks down to form dinitrogen oxide and water. NH4NO3(s)  N2O(g) + 2H2O(g) Look at the formula for magnesium nitride, Mg3N2 . What elements do you see in this formula? You see magnesium and nitrogen. Now we can write a decomposition reaction for magnesium nitride. Mg3N2(s) 3 Mg(s) +N2(g) Notice there is only one reactant

Sample Problem 2 Write the chemical equation for the decomposition of the following compounds into their individual elements: Al2O3 2 Al2O3  4 Al+3 O2 Ag2S Ag2S  2 Ag+S

Single Replacement Reactions A third type of reaction is the single replacement reaction. In single replacement reactions, one element reacts with one compound to form products. There are actually three different types of single replacement reactions: The single element is a metal and replaces the metal in the second reactant The single element is a metal and replaces the hydrogen in the second reactant, which is always an acid The single element is a nonmetal and replaces the nonmetal in the second reactant.

Replacement of a Metal with a Metal In this section, we will focus on single replacement reactions where an elemental metal reactant replaces the metal (or the cation) of a second compound. The general equation for this reaction is: A + BC  B + AC Consider the following example. Notice there is only one reactant that is an element and one reactant that is a compound. Zn(s) + Cu(NO3)2(aq)  Zn(NO3)2(aq) + Cu(s)

Example 1 Predict the products for the following reaction: Fe+CuSO4 Fe(s)+CuSO4(aq)  Cu(s)+FeSO4(aq) Predict the products for the following reaction: Al+CuCl2 2 Al+3 CuCl2  3 Cu+2 AlCl3

Replacement of Hydrogen with a Metal These reactions are the same as those studied in the last slide, except the compound in the reactant side of the equation is always an acid. an acid is a compound in which hydrogen is combined with an anion The General reaction is: A + 2 HX  AX2 + H2 The chemical equation below is an example of this type of reaction: Zn(s)+2 HBr(aq)  ZnCl2(aq) + H2(g)

Example 2 Predict the products for the following reaction Zn(s) + H2SO4(aq) Zn(s) + H2SO4(aq)  ZnSO4(aq) + H2(g) Al(s) + HNO3(aq) 2 Al(s) + 6 HNO3(aq)  2 Al(NO3)3(aq) + 3 H2(g)

Replacement of a Nonmetal with a Nonmetal We will focus on the final type of single replacement reactions where the element reactant replaces the nonmetal (or the anion) in a compound. The general equation for this type of reaction is: A + BC  C + BA Notice in the equation below that the chlorine replaced the iodine to produce solid iodine as a product. The only difference here is that we have to remember that we are replacing the anion of the compound rather than the cation. Cl2(g) +2 KI(aq)  2 KCl(aq) + I2(s)

Example 3 Write the chemical equation for the single replacement reaction between sodium iodide solution and liquid bromine to produce sodium bromide solution and solid iodine. 2 NaI(aq) +Br2(l)  2 NaBr(aq) + I2(s) Predict the products for the following reaction: Br2(aq) + KI(aq) Br2(aq) + 2 KI(aq)  2 KBr(aq) + I2(s)

Double Replacement For double replacement reactions, two reactants will react by having the cations exchange places. The key to identifying this type of reaction is to recognize that it has two compounds as reactants. Precipitation and neutralization reactions are two of the most common double replacement reactions. Precipitation reactions are ones where two aqueous reactants combine to form products where one of the products is an insoluble solid. A neutralization reaction is one where the two reactant compounds are an acid and a base and the two products are a salt and water. The following is a precipitation reaction because AgCl(s) is formed. AgNO3(aq) + NaCl(aq)  AgCl(s) + NaNO3(aq)

Example 4 Write a chemical equation for the double replacement reaction between calcium chloride solution and potassium hydroxide solution that produces potassium chloride solution and a precipitate of calcium hydroxide CaCl2(aq) +2 KOH(aq)  Ca(OH)2(s) +2 KCl(aq) Predict the products for the following reaction: AgNO3(aq) + NaCl(aq) AgNO3(aq) + NaCl(aq)  AgCl(s) + NaNO3(aq)

Combustion In a combustion reaction, oxygen reacts with another substance to produce carbon dioxide and water. This is a special type of single replacement reacion A hydrocarbon is an organic substance consisting of only hydrogen and carbon. Combustion reactions usually have a hydrocarbon reacting with oxygen to produce CO2 and H2O . The only part that changes from one combustion reaction to the next is the actual hydrocarbon involved in the reaction. The general equation for this reaction is given below. Oxygen, carbon dioxide, and water are listed in the products because they remain the same for all combustion reactions Hydrocarbon + O 2(g)  CO2(g) + H2O(l) Example 2 C8H18(l) + 25 O2(g)  16 CO2(g) + 18 H2O(l)

Incomplete Combustion Have you ever seen the black puffs of smoke come out from the exhaust pipe of a car? If there is not enough oxygen, the result is an incomplete combustion reaction with CO(g) and C(s) (in the form of soot) also formed as products. Incomplete combustion reactions are actually quite dangerous because one of the products in the reaction is carbon monoxide, not carbon dioxide. Carbon monoxide is a gas that prevents oxygen from binding to the oxygen transport proteins in our blood cells. When the concentration of carbon monoxide in the blood becomes too high, not enough oxygen can be transported and the person can die.

Example 5 C7H16(l) + O 2(g)  CO2(g) + H2O(l) Complete; C7H16(l) +11 O2(g)  7 CO2(g) +8 H2O(l) C3H8(g)+ O 2(g)  CO2(g) + H2O(l) Complete; C3H8(g) +5 O2(g)  3 CO2(g) + 4 H2O (l) CH4(g) + O 2(g)  CO(g) + H2O(l) Incomplete; 2 CH4(g) +3 O2(g)  2 CO(g) + 4 H2O(l)

Check List for All Chemical Reactions Make sure the ionic compounds are balanced properly Make sure the equation is properly balanced Make sure all phases are recorded properly (s, l, g, aq)

Lesson Summary Synthesis Two or more reactants form one product Reaction Name Reaction Description Synthesis Two or more reactants form one product Decomposition One type of reactant forms two or more products Single Replacement One element reacts with one compound to form products Double Replacement Two compounds act as reactants Combustion A hydrocarbon reacts with oxygen gas

Practice Problems 1 Distinguish between synthesis and decomposition reactions. Synthesis takes two or more reactants and makes one product Decomposition takes one reactant and breaking it down to two or more parts When dodecane, C10H22 , burns in excess oxygen, the products would be: CO2+2 H2 CO+H2O CO2+H2O CH4O2

Practice Problems 2 In the decomposition of antimony trichloride, which of the following products and quantities will be found? An + Cl2 2 An + 3 Cl2 Sb + Cl2 2 Sb + 3 Cl2