Types of Chemical Reactions

Writing Chemical Reactions

Types of Reactions Many chemical

reactions have defining characteristics which allow them to be classified as to type.

Types of Chemical Reactions

The five types of chemical reactions in this unit are: Combination Decomposition Single Replacement Double Replacement Combustion

Combination Reactions Two or more substances combine to

form one substance. The general form is A + X AX

Example: Magnesium + oxygen

magnesium oxide 2Mg + O2 2MgO

Combination Reactions Combination reactions may also be

called composition or synthesis reactions.

Some types of combination reactions: Combination of elements

K + Cl2 One product will be formed

Combination Reactions K + Cl2

Write the ions: K+ Cl-

Balance the charges: KCl

Balance the equation: 2K + Cl2 2KCl

Combination Reactions Some types of combination

reactions:Oxide + water

Nonmetal oxide + water acidSO2 + H2O H2SO3

Metal oxide + water baseBaO + H2O Ba(OH)2

Combination Reactions Some types of combination

reactions:Metal oxides + nonmetal oxidesNa2O + CO2 Na2CO3CaO + SO2 CaSO3

Predicting products for synthesis reaction

• Write down the reactants that are involved in the reactions on the reactant sideof the equations.

• Knowing that a synthesis reaction is going to occur, put the reactants togetheron the product side of the equation.

• When elements make compounds remember that there is a certin ratiowhich they must combine in. YOU MUST REMEMBER HOW TO WRITE CHEMICAL FORMULAS.

Lets continue looking at the potassium and chlorine reaction.

Combination Reactions K + Cl2

Write down the formula for potassium chloride. KCl

Notice you are missing a Cl atom on the product side. Where did that Chlorine atom go?

No where Balance the equation: 2K + Cl2 2KCl

One more thing to remember when writing equations

Diatomic elements• Elements that never travel alone.

Last example of potassium and chlorineReactants K + Cl2Product KCl

Notice the Chlorine is never by itself this is a diatomic element

How do you remember the diatomic elements?

H.O.Br.F.I.N.ClH – hydrogenO – oxygenBr – BromineF – FluorineI – IodineN – NitrogenCl - Chlorine

PracticePredict the following products.Write a balanced chemical equation for each of the following

Copper + oxygen

Silver + Sulphur

Iron + Oxygen

2Cu + O2 2CuO

2Ag + S Ag2S

3Fe + O2 Fe3O2

Decomposition Reactions

One substance reacts to form two or more substances. The general form is AX A + X

Example: Water can be decomposed by

electrolysis. 2H2O 2H2 + O2

Decomposition Reactions

Types of Decomposition Reactions: Decomposition of carbonates

When heated, some carbonates break down to form an oxide and carbon dioxide.

CaCO3 CaO + CO2H2CO3 H2O + CO2

Decomposition Reactions

Types of decomposition reactions: Some metal hydroxides

decompose into oxides and water when heated.Ca(OH)2 CaO + H2O

Note that this is the reverse of a similar combination reaction.

Decomposition Reactions

Types of decomposition reactions: Metal chlorates decompose into

chlorides and oxygen when heated.2KClO3 2KCl + 3O2Zn(ClO3)2 ZnCl2 + 3O2

Some of these reactions are used in explosives.

Decomposition Reactions

Some substances can easily decompose: Ammonium hydroxide is actually

ammonia gas dissolved in water.NH4OH NH3 + H2O

Some acids decompose into water and an oxide.H2SO3 H2O + SO2

Summary synthesis V.s Decomposition Synthesis

• Non-metal oxide + H2O AcidCO2 + H2O HCO3

• Metal oxide + water Base BaO + H2O Ba(OH)2

• Metal oxide + non-metal oxide polyatomic compound

CaO + SO2 CaSO3Decomposition

• Acid decomposition HCO3 CO2 + H20

• Hydroxide decompositionBa(OH)2 BaO + H2O

• Polyatomic compound decompositionCaSO3 CaO + SO2

Decomposition Reactions

Some decomposition reactions are difficult to predict.

The decomposition of nitrogen triiodide, NI3, is an example of an interesting decomposition reaction.

Single Replacement Reactions

A metal will replace a metal ion in a compound. The general form is A + BX AX +

B

A nonmetal will replace a nonmetal ion in a compound. The general form is Y + BX BY +

X

Single Replacement Reactions

Examples: Ni + AgNO3

Nickel replaces the metallic ion Ag+. The silver becomes free silver and the

nickel becomes the nickel(II) ion. Ni + AgNO3 Ag + Ni(NO3)2

Balance the equation: Ni + 2AgNO3 2Ag + Ni(NO3)

Single Replacement Reactions

Not all single replacement reactions that can be written actually happen.

The metal must be more active than the metal ion.

Aluminum is more active than iron in Al + Fe2O3 in the following reaction:

Thermite Reaction

Thermite Reaction Al + Fe2O3 Aluminum will replace iron(III) as

was seen in the video. Iron (III) becomes Fe and

aluminum metal becomes Al3+. 2Al + Fe2O3 2Fe + Al2O3

Single Replacement Reactions

An active nonmetal can replace a less active nonmetal.The halogen (F2, Cl2, Br2, I2) reactions are good examples.

F2 is the most active and I2 is the least.Cl2 +2 NaI 2 NaCl + I2

Double Replacement Reactions

Ions of two compounds exchange places with each other.The general form is AX + BY AY + BX

Metathesis is an alternate name for double replacement reactions.

Double Replacement NaOH + CuSO4 The Na+ and Cu2+ switch places. Na+ combines with SO4

2- to form Na2SO4.

Cu2+ combines with OH- to form Cu(OH)2

NaOH + CuSO4 Na2SO4 + Cu(OH)2 2NaOH + CuSO4 Na2SO4 + Cu(OH)2

Double Replacement CuSO4 + Na2CO3 Cu2+ combines with CO3

2- to form CuCO3.

Na+ combines with SO42- to form

Na2SO4. CuSO4 + Na2CO3 CuCO3 +

Na2SO4

Double Replacement Na2CO3 + HCl Na+ combines with Cl- to form

NaCl. H+ combines with CO3

2- to form H2CO3.

Na2CO3 + 2HCl 2NaCl + H2CO3 H2CO3 breaks up into H2O and

CO2.

Double Replacement The gas formed was carbon

dioxide. The final balanced reaction is:

Na2CO3 + HCl NaCl + H2O + CO2.

Balance the equation. Na2CO3 + 2HCl 2NaCl + H2O +

CO2

Combustion Reaction When a substance combines with

oxygen, a combustion reaction results.

The combustion reaction may also be an example of an earlier type such as 2Mg + O2 2MgO.

The combustion reaction may be burning of a fuel.

Combustion Reaction Methane, CH4, is natural gas. When hydrocarbon compounds

are burned in oxygen, the products are water and carbon dioxide.

CH4 + O2 CO2 + H2O CH4 + 2O2 CO2 + 2H2O

Combustion Reactions Combustion reactions involve

light and heat energy released. Natural gas, propane, gasoline,

etc. are burned to produce heat energy.

Most of these organic reactions produce water and carbon dioxide.

Practice Classify each of the following as

to type:

H2 + Cl2 2HCl Combination

Ca + 2H2O Ca(OH)2 + H2 Single replacement

Practice 2CO + O2 2CO2

Combination and combustion

2KClO3 2KCl + 3O2 Decomposition

Practice FeS + 2HCl FeCl2 + H2S

Double replacement

Zn + HCl ? Single replacement Zn + 2HCl ZnCl2 + H2