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Types of Chemical Reactions

If you add two substances together sometimes you get a chemical reaction. This is when a new substance is made.

It is very difficult to reverse the reaction and get the original substances back.

Signs that a chemical reaction has taken place include a change in colour, heat being given off or bubbles of gas being made.

Adding acid to alkali

Fireworks Driving a car

Ice cream melting

Boiling the kettle frying an egg

Burning a candle Melting candle wax

Dissolving sugar in tea

Lighting a matchMaking ice cubes

Ironing clothes

Printing Baking a cake Launching a space rocket

Discuss in pairs which of these are chemical reactions

x x

x x

xx

x

The changes that are not chemical changes are called physical changes

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Objectives

Define and give general equations for synthesis, decomposition, single-replacement, and double-replacement reactions.

Classify a reaction as synthesis, decomposition, single-replacement, single-replacement, double-replacement, or combustion.

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Objectives List three types of synthesis reactions

and six types of decomposition reactions.

List four types of single-replacement reactions and three types of double-replacement reactions.

Predict the products of single reactions given the reactants.

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Background Thousands of known chemical reactions

occur in various systems. Memorizing the equations for so many chemical reactions would be difficult. It is more useful and realistic to classify reactions according to various similarities and regularities.

+ The 5 Types of Reactions

DoubleReplacement

Decomposition

Single Replacement

Synthesis

Combustion

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Synthesis Reactions In a synthesis reaction, also known as

composition reaction, two or more substances combine to form a new compound.– General equation: A + X AX.

Types of synthesis reactions:– Reactions of elements with oxygen and sulfur.– Reactions of metals with halogens.– Synthesis reaction with oxides.

+Synthesis Reaction

Synthesis reaction – 2 substances combine to form a single product

A + B AB+

2Mg(s) + O2(g) 2MgO(s)Magnesium and oxygen combine to form magnesium

oxide.

2H2(g)+ O2(g) 2H2O(l)Hydrogen and oxygen combine to form dihydrogen

monoxide

Look at the reactants represented below, which reaction involves elements as reactants? Which reaction involves compounds as reactants?

Synthesis reaction Decomposition reaction

A synthesis reaction involves the combination smaller molecules

A decomposition reaction involves the breaking apart of larger molecules

LETS US LOOK AT TWO OF THE REACTION TYPES:SYNTHESIS AND DECOMPOSITION

Recognizing the types of reactants is key to identifying the reaction type

Synthesis Reactions

• Involve the combination of smaller atoms and /or molecules into larger molecules.

• They are also called combination reactions

• General formula

• A + B AB

• If you see two elements as reactants, you know the reaction has to be a sysnthesis reaction

• Synthesis reactions can also involve combinations of small molecules.

• For example, when ammonia and hydrogen chloride vapours combine, they form a white smoke as solid particles of ammonium chloride are formed.

Hydrogen chloride + ammonia ammonium chlorideHCl + NH3 NH4Cl

TYPICAL EXAMPLE , RAINWATER

Similarly, combination of water and carbon dioxide molecules Synthesis reaction

CO2 + H2O H2CO3(aq)

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Examples of Reaction of Elements with Oxygen and Sulfur:– Forming Oxides and sulfides:

2Mg(s) + O2(g) 2MgO(s)

16Rb(s) + S8(s) 8Rb2S(s)

8Ba(s) + S8(s) 8BaS(s)

S8(s) + 8O2(g) 8SO2(g)

C(s) + O2(g) CO2(g)

2C(s) + O2(g) CO(g)

2H2(g) + O2(g) 2H2O(l)

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– Forming Oxides and sulfides: 2Fe(s) + O2(g) 2FeO(s)

4Fe(s) + 3O2(g) 2Fe2O3(s)

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Reactions of Metals with Halogens (most metals react with the halogens (group 17) to form either ionic or covalent compounds.– Group 1 metals with Group 17 elements

2Na(s) + Cl2(g) 2NaCl(s)

2K(s) + I2(g) 2KI(s)

– Group 2 metals with Group 17 elements Mg(s) + F2(g) MgF2(s)

Sr(s) + Br2(l) SrBr2(s)

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– Fluorine is so reactive that it combines with almost all metals:

2Na(s) + F2(g) 2NaF(s)

2Co(s) + F2(g) 2CoF3(s)

U(s) +3F2(g) UF6(g) Practical application with fluorine:

– Sodium fluorine added to municipal water supplies.– Cobalt(III) fluoride is a strong fluorinating agent.– Uranium(VI) fluoride is the first step in the production

of uranium for use in nuclear power plants.

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Synthesis Reactions with Oxides– Oxides of active metals react with water to

produce metal hydroxides - example CaO(s) + H2O(l) Ca(OH)2(s)

– Many oxides of nonmetals (upper right portion of the periodic table) react with water to produce oxyacids - example

SO2(g) + H2O(l) H2SO3(aq) this reacts with oxygen to produce sulfuric acid

2H2SO3(aq) + O2(g) 2H2SO4(aq)

– Certain metal oxides and nonmetal oxides react with each other in synthesis reaction to form salts. CaO(s) + SO2(g) CaSO3(s)

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Decomposition Reactions

In a decomposition reaction, a single compound undergoes a reaction the produces two or more products.– General equation AX A + X

Decomposition Reactions

• It involve the splitting of a large molecule into elements or smaller molecules.

• General formulaAB A + B

• Example, electrolysis of water uses electricity to split water molecules into their elements

water hydrogen + oxygenH2O H2 + O2

2H2O 2H2 + O2

+Decomposition ReactionDecomposition reaction – A single compound breaks

down into 2 or more products.

AB A + B +

2H2O2(aq) O2(g)+ 2H2O(l)Hydrogen peroxide decomposes into oxygen gas and dihydrogen

monoxide.

2NaCl(s) 2Na(s) + Cl2(g)Sodium chloride decomposes into sodium and chlorine gas.

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Types of decomposition reactions– Decomposition of Binary Compounds– Decomposition of Metal Carbonates– Decomposition of Metal Hydroxides– Decomposition of Metal Chlorates– Decomposition of Acids

Decomposition of Binary Compounds electricity

– 2H2O(l) 2H2(g) + O2(g) (called electrolysis)

2HgO(s) 2Hg(l) + O2(g)

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Decomposition of Metal Carbonates– CaCO3(s) CaO(s) + CO2(g)

Decomposition of Metal Hydroxides– Ca(OH)2(s) CaO(s) + H2O(g)

Decomposition of Metal Chlorates– 2KClO3(s) 2KCl(s) + 3O2(g)

Decomposition of Acids– H2CO3(aq) CO2(g) + H2O(l)

– H2SO4(aq) SO3(g) + H2O(l)

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Single-Replacement Reactions

In a single-replacement reaction, also know as a displacement reaction, one element replaces a similar element in a compound.– A + BX AX + B or– Y + BX BY + X

Single Displacement Reactions• Are chemical changes

that involve an element and a compound as reactants.

• One element displaces or replaces another element from the compound.

• Example, when magnesium ribbon is placed in a solution of silver nitrate

Mg + AgNo3 Ag + Mg(NO3)2

Mg + 2AgNO3 2Ag + Mg(NO3)2

+Single Replacement Reaction

Single Replacement reaction – A single element takes the place of another element in a compound.

A + BC C + AB

+ +

AgNO3(aq) + Cu(s) Ag(s) + CuNO3(aq)Copper replaces silver in silver nitrate to copper (I) nitrate and silver.

Zn(s) + 2HCl(aq) H2(g) + ZnCl2(aq)Zinc replaces hydrogen in hydrogen chloride to yield hydrogen gas and zinc

chloride.

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Types of single-replacement reactions– Replacement of a Metal in a Compound by

Another Metal– Replacement of Hydrogen in Water by a

Metal– Replacement of Hydrogen in Acid by a Metal– Replacement of Halogens

Replacement of a Metal in a Compound by Another Metal. – A more active metal will replace a less active metal.– 2Al(s) + 3Pb(NO3)2(aq) 3Pb(s) + 2Al(NO3)3(aq)

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Replacement of Hydrogen in Water by a Metal – The most-active metals such as those in Group 1,

react vigorously with water to produce metal hydroxides and hydrogen.

– example 2Na(s) + 2H2O(l) 2NaOH(aq) + 4H2(g)

– example 3Fe(s) + 4H2O(g) Fe3O4(s) + 4H2(g) (Less-active metals react with steam to form a metal oxide and hydrogen gas)

Replacement of Hydrogen in an Acid by a Metal

– The more-active metals react with certain acidic

solutions replacing the hydrogen in the acid. – example Mg(s) + 2HCl(aq) H2(g) + MgCl2(ag)

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Replacement of Halogens – One halogen replaces another halogen in a

compound. Fluorine is the most-active halogen and can replace any other halogen in their compounds.

– Cl2(g) + 2KBr(aq) 2KCl(aq) + Br2(l)

– F2(g) + 2NaCl(aq) 2NaF(aq) + Cl2(s)

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Double-Replacement Reactions

In double-replacement reactions, the ions of two compounds exchange places in an aqueous solution to form two new compounds.– General equation AX + BY AY + BX

Formation of a Precipitate– The formation of a precipitate occurs when the

cations of one reactant combine with the anions of another reactant to form an insoluble or slightly soluble compound.

– 2KI(aq) + Pb(NO3)2(aq) PbI2(s) + 2KNO3(aq)

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Formation of a Gas– In some double-replacement reactions, one of the

products in an insoluble gas that bubbles out of the mixture.

– FeS(s) + 2HCl(aq) H2S(g) + FeCl2(aq)

Formation of Water– In some double-replacement reactions, a very

stable molecular compound, such as water, is one of the products.

– HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)

+Double Replacement Reaction

Double Replacement reaction – Elements in 2 compounds switch places to form 2 new compounds.

AB + CD AD + CB+ +

HCl(aq) + NaOH(aq) HOH(l) + NaCl(aq)Hydroxide and chlorine switch places to hydrogen hydroxide (water) and sodium

chloride

Na2S(aq) + Zn(NO3)2(aq) 2NaNO3(aq) + ZnS (s)Sulfur and nitrate switch places to form sodium nitrate and zinc sulfide.

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Combustion Reactions In a combustion reaction, a substance

combines with oxygen, releasing a large amount of energy in the form of light and heat.– 2H2(g) + O2(g) 2H2O(g)

– C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(g)

+Combustion Reaction

Combustion reaction – A hydrocarbon (H and C) burn in oxygen to produce water and carbon dioxide. Heat is given off as energy.

CxHx + O2 H2O + CO2 + heatCH4(g) + 2O2(g) 2H2O (l) + CO2(g)

Methane burns in oxygen to produce water and carbon dioxide.

C12H22O11(s) + 12O2(g) 11H2O(l) + 12CO2(g)Sucrose burns in oxygen to produce water and carbon dioxide.

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Section Review List five types of chemical reactions. Complete and balance each of the following

reactions identified by type:– synthesis: ______ Li2O

– decomposition: Mg(ClO3)2 ______

– single-replacement: Na + H2O ______

– double-replacement: HNO3 +Ca(OH)2

– combustion: C5H12 + O2 ______

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Section Review

Classify each of the following reactions:– N2(g) + 3H2(g) 2NH3(g)

– 2Li(s) + 2H2O(l) 2LiOH(aq) + H2(g)

– 2NaNO3(s) 2NaNO2(s) + O2(g)

– 2C6H14(l) + 19O2(g) 12CO2(g) +14H2O(l)

– NH4Cl(s) NH3(g) + HCl(g)

– BaO(s) + H2O(l) Ba(OH)2(aq)

– AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)