Types of Chemical Reactions

5 Main Categories

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Acid/Base Reactions

Chemical Reactions

• In a chemical reaction, bonds between compounds are broken and new compounds are formed.

• In a chemical reaction, elements can also react to form new compounds.

• Reactants ------- form ------- products

• There are 5 main categories of reactions. They all have different characteristics or

KEY POINTS to help you recognize them.

• In addition we will look at acid/base reactions which can also be characterized as double replacement reactions.

Combination Reactions

• Reactants are forming one product

• The product is always a SINGLE compound.

Products of Combination Rxns

• When a metal and a nonmetal react, the product is an ionic compound.

• EXAMPLE

2K + Cl2 -------- 2KCl

NOTE: A single compound is the product

Combination Cont.• When 2 nonmetals react, more than

one combination of product is possible

EXAMPLES (s) + O2 (g) -------- SO2 (g)

2S (s) + 3O2 (g) ------- SO3 (g)

NOTE:

A single product is the result of each reaction

Combination Cont.

• When a transition metal reacts, more than one possible product may result.

• EXAMPLE

Fe (s) + S (s) --------- FeS (s) Iron (II) Sulfide

2Fe (s) + 3S (s) ------ Fe2S3 (s) Iron (III) Sulfide

NOTE: Still a single product for each reaction results.

How do you know then?• If you are asked to write the

products of any reaction where there may be more than one possible product, the name of the product will be given to you.

• Remember to include Roman Numerals for these transitions metals, (Roman numerals give the charge of the metal)

Decomposition Reactions

• In decomposition reactions, a single reactant is present.

• The single reactant breaks down to form other compounds or elements. In effect, it decomposes.

• A SINGLE REACTANT is present.

Decomposition Reactions

• A single compound reactant is broken down into two or more products

• When a single binary compound breaks down, its product will be the constituent elements.

• EXAMPLE

HI ------------ H2 + I2

Decomposition Cont.

• If the compound is not binary, the names of the products will be given to you

• EXAMPLE

–CaCO3 --- Calcium oxide + carbon dioxide

–CaCO3 --- CaO + CO2

Single Replacement Reactions

• In a single replacement reaction, a single element will replace a similar element in a compound. Na + ZnO ------- Na2O + Zn (Na takes the place of Zn)

F + NaBr -------- NaF + Br2 (In this case, the non-metal

(F) replaces the non-metal Br- they are similar to each other).

A single element is one of the reactants.

Single Replacement Reactions

• One element replaces another element in the reaction

• Usually a metal replaces another metal, but single non-metals will replace non-metals in compounds.

• Not all metals will replace all other metals

• Whether they will or not is determined by how “active” they are.

– We know for ex. That lithium is a very “re-active” metal. It will replace any other metal it encounters.

Single Replacement Cont.

• Whether metals will replace each other and allow the reaction to occur is determined by a chart called the Activity Series of Metals

• There is one listed.

• lithium • potassium • strontium • calcium • sodium • magnesium • aluminum • zinc • chromium • iron cadmium • cobalt • nickel • tin • lead • HYDROGEN • antimony • arsenic • bismuth • copper • mercury • silver • paladium • platinum • gold

Metal Reactivity Chart

They are in order of most reactive (lithium) to least reactive (gold)

S-R CONT.

The way to use this series is If the single metal reactant is higher

on the list than the metal it is replacing in the compound, the reaction will occur.

EXAMPLEMg + Zn(NO3)2 -- Mg(NO3)2 + Zn

Look at the series and note that Mg is higher on the series than Zn, so the rxn proceeds.

S-R CONT.

• Look at the next example and predict whether you think the reaction will occur

• Mg + LiNO3-----

• HINT- Check the series. Is Mg higher on the list than Li?

S-R CONT

• The answer is no. Mg is not higher than Li on the list, so the reaction below is a no-go!

• Mg + LiNO3 ------ no reaction

S-R CONT.

• One small rule to keep in mind on the activity series

–Metals from Li to Na will replace H from acids and water

–Metals from Mg to Pb will replace H from acids only.

Examples with Hydrogen

• Li + HOH -------- LiOH + H2

• Ca + HNO3 -------- Ca(NO3)2 + H2

• Zn + HOH---------- no reaction (Zn won’t replace H in water- Zn is below sodium)

• Zn + HNO3 --------- Zn(NO3)2 + H2 (In this case, Zn will replace H from the acid)

Double Replacement Reactions

• In these reactions, the positive ions in two ionic compounds, exchange places

2 ionic compounds are the reactants.

• EXAMPLE

– Na2S + Cd(NO3)2- CdS + 2NaNO3

• Note that Na took the place of Cd and vice versa

– Ca(OH)2 + 2HCl - CaCl2 + 2H2O

Combustion Reactions

In these reactions, an element or compound reacts with O2 (oxygen) often producing energy as heat and light.

O2 is one of the reactants.

EXAMPLE2Mg + O2 --- 2 MgO

S + O2 --- SO2

Combustion Cont.

• Many combustion reactions involve a hydrocarbon, a compound made of hydrogen

and carbon.

Hydrocarbons and O2 will ALWAYS produce H2O and CO2.

• If this is the case, the products will always be CO2 and H2O, carbon dioxide and water.

• EXAMPLE:

–2C6H6 + 15O2 ---- 12 CO2 + 6H2O

Your TURN• IDENTIFY THE TYPE OF REACTION

BELOW

• C6H12O6 + O2 -- 6CO2 + 6H2O

• KOH + H3PO4 - K3PO4 + 3H2O

• Mg(ClO3)2 --- MgCl2 + 3O2

• Fe + Pb(NO3)2 - Fe(NO3)2 + Pb

IDENTIFY

• Cl2 + NaI -- 2NaCl + I2

• H2O -- H2 + O2

• Be + O2 ------ 2BeO

FINAL NOTES (for 2day)

• Remember that there are 7 diatomic molecules – Diatomic molecules are reactive

elements that rarely exist alone. So, they form a molecule with themselves

• H2, N2, O2, F2, Cl2, Br2, I2

• This is useful when writing reactions correctly.

EXAMPLE

• Write the equation: – Potassium reacts with oxygen to

produce potassium oxide.

– K + O2 ---- K2O

People would be tempted to write

K + O-- K2O and that would be wrong