Types ofChemical Reactions

1. Synthesis Reactions• A synthesis reaction occurs when two or more

simple substances combine to produce a more complex substance.

• AKA: Combination reaction.• The general equation for a synthesis is:

A + B AB• HINT: If there is only one product – it is likely a

synthesis.

Examples of Synthesis Reactions• CO2 + H2O H2CO3

• 4Fe + 3O2 2Fe2O3

• Li2O + H2O 2LiOH

2. Decomposition Reactions

• A decomposition reaction occurs when a complex substance is broken down into two or more simpler substances.

• Heat is often used to aid in decomposition reactions – these reactions that employ heat are called thermal decompositions.

• Decompositions and synthesis reactions are opposites.• The general equation for a decomposition reaction is:

AB A + B• HINT: If there is only one reactant – it is likely a

decomposition reaction.

Examples of Decomposition Reactions:• NH4NO3 N2O + 2H2O• Ca(OH)2 CaO + H2O• 2H2O2 2H2O + O2

3. Single Displacements

• A single displacement reaction occurs when a single element takes the place of one of the elements in a compound.

• AKA: Single Replacement• The general equation for a single displacement

reaction is:AB + Z ZB + A

• Metals displace metals while nonmetals displace nonmetals.

• HINT: The single mysterious loner moves into town and breaks up the happy couple!

Examples of Single Displacement Reactions• Fe + CuSO4 FeSO4 + Cu• 2K + MgO K2O + Mg• 2CuF + Ba BaF2 + 2Cu

Not So Fast There…• The lone element doesn’t always break up the couple!

We can use a tool called the activity series to predict if the compound will stay together or break up.

• The activity series is a list of metals and hydrogen that are arranged in order of reactivity.

Li K Ba Ca Na Mg Al Zn Fe Ni Sn Pb H Cu Hg Ag Au

• The rule is that you can only be displaced by an element that is to the left of you. This makes Lithium the strongest and Gold the weakest.

• There is also a halogen activity series – it is used to predict reactions with halides.

F Cl Br I

Using the Activity Series

You can use the activity series in three ways:1) Straight forward Single Displacements2) Reactions with Acids3) Reactions with Water

• Straight Forward Single Displacements– Use the rule of “whoever is more to the left wins” to

see if there is a reaction or not.• Reactions with Acids

– Acids contain hydrogen (positive like the metals). If you are to the left of hydrogen – you react and take its place – if you are to the right – there is no reaction.

• Reactions with Water– Only the first five elements (Li K Ba Ca Na) will react

with water. It will form a hydroxide and hydrogen gas.

4. Double Displacements

• A double displacement reaction always involves two ionic compounds that switch partners with each other.

• Again, positive ions switch with positive ions (and/or vice-versa).

• The general equation for a double displacement reaction is:

AB + XY AY + XBHINT: Two couples switch partners at the dance.

Examples of Double Displacement Reactions:• Pb(NO3)2 + 2KI PbI2 + 2KNO3

• Na2SO3 + 2HCl 2NaCl + H2SO3

• 2NaOH + H2SO4 2H2O + Na2SO4

Not So Fast There…Again!

• There are three outcomes for a double displacement reaction:

1) Precipitate – solid formed from two liquids.• Use the solubility rules.

2) Gas – some compounds form products that break down further into gases.

3) Water – results from a neutralization between an acid and a base.

5. Combustion Reaction

• A combustion reaction occurs when a substance (the “fuel”) reacts very rapidly with oxygen to form carbon dioxide and water.

• Combustion reactions release a good deal of energy in a very short period of time.

• The general equation for a combustion reaction is:

Fuel + O2 CO2 + H2O

• HINT: Something combines with oxygen to produce carbon dioxide and water.

Incomplete Combustion

• If a combustion occurs at a lower temperature, it may result in an incomplete combustion.

• The products of an incomplete combustion are water, carbon dioxide, carbon monoxide and carbon (a solid residue).

• The general equation is:

Fuel + O2 H2O + CO2 + CO + C

THE END