Types of Chemical Reactions

There are four types of chemical reactions.

The first is Synthesis.

Synthesis means to put things together.

The general form is A + B = AB. It is combining two reactants to make one product.

You simply combine two pure elements which form one compound. It can also be two small compounds that form a large compound, or elements → compound

Examples:

Zn (Zinc) + S (Sulfur) = ZnS (Zinc Sulfide)

Mg (Magnesium) + O2 (Oxygen) = MgO (Magnesium Oxide)

The synthesis reaction with a non-metal oxide and water (H2O) will create an acid.

e.g CO2 (Carbon Dioxide) + H2O (Water) = H2CO3 (Carbonic Acid)

e.g SO3 (Sulfur Trioxide) + H2O (Water) = H2SO4

The synthesis reaction with a metal oxide and water will create a metal hydroxide.

e.g Sodium Oxide reacting with water → Sodium Hydroxide

Na2O +                 H2O        —>       NaOH

^ Sodium Oxide    ^ Water                ^  Sodium Hydroxide

The second is Decomposition.

Decompose means to come apart.

It is essentially the reverse of synthesis.

The general form is AB → A + B.

These reactions are endothermic, meaning they take in heat, and the reactant needs energy to be pulled apart into the products.

You pull apart a compound to get two substances, or compound → elements

e.g Hydrogen peroxide decomposing into water and oxygen in the presence of light (heat,energy)

H2O2                     →             H2O             + O2

^ A compound         ^ light(heat/energy)         ^ Two substances

  • The simple decomposition has a general form of: compounds → elements

Sodium Azide (n3-) → Sodium + Nitrogen

2 NaN3 → 2 Na + 3 N2

  • The decomposition of oxyacids:

Oxyacid → non-metal oxide + water

e.g sulfurous acid is heated

H2SO3                      →          SO2                      +        H2O

^ Sulfurous Acid     ^ heat        ^ Sulfur Dioxide             ^ Water

  • The decomposition of metal hydroxides [OH]

Metal Hydroxide → metal oxide + water

e.g Aluminum Hydroxide is heated

Al(OH)3 -→ Al2O3 + H2O

^ Metal Hydroxide ^ heat ^ metal oxide ^ water

The decomposition of metal carbonates [CO3]

Metal Carbonate → metal oxide + carbon dioxide

Na2CO3 → Na2O + CO2

^ sodium carbonate ^ sodium oxide ^ carbon dioxide

The decomposition of metal chlorates

Metal Chlorate → Metal Chloride + Oxygen

e.g Barium chlorate is heated → Barium chloride + oxygen

Ba(ClO3)2                →          BaCl2              +          O2

^ barium chlorate    ^ heat      ^ Barium chloride       ^ Oxygen

The third reaction is Combustion.

Something (like fuel) is typically burning. The fuel reacts with oxygen to produce heat energy, which then forms two reactants: Carbon Dioxide CO2 and Water H2O. 

The general form is Fuel + O2 = CO2 + H2O + Energy.

or C#H# (Hydrocarbon) + O2 (Oxygen) =  CO2 + H2O + Energy/Heat

or substance + OXYGEN → oxide of each element in the reacting substance

Complete Combustion: The oxygen in the reactants being sufficient, being able to produce common oxides of the elements in the reactant.

Incomplete Combustion: Oxygen being insufficient, which can result in CO (kills you) or C (black powder)

e.g of examples of combustion products

Carbon = CO2

Hydrogen = H2O

Nitrogen = NO2

Sulphur = SO2

Metals = metal oxide (ionic)

  • Have some hydrocarbon, which reacts with oxygen, which results in carbon dioxide, water, and energy being produced? That’s combustion.

The third reaction is Single Displacement.

! It’s helpful to write H2O as HOH.

! Check the Activity Series.

A more-reactive element displaces a less-reactive element in a compound, which results in a new compound and a new element.

The general form is:

A (pure element) + BC (compound) = AC (A being apart of a compound) + B (B being a pure element)

Where A is a more-reactive element than B, so it kicks out B and becomes a compound with C.

  • Metals tend to displace other metals, or cations (positive ions)

  • Non-metals tend to displace other non-metals, or anions (negative ions)

e.g 

Zn + CuCl2         →    ZnCl2 + Cu

A   +  B C         →   A    C  +  B

Here, Zinc metal has displaced Copper metal, becoming a compound with chlorine (zinc chloride), kicking out copper as a pure element.

e.g 

Br2 + NaI -→ NaBr + I2

A     +   BC    →   AC       +   B

Here, Bromine non-metal liquid has displaced Iodine non-metal liquid, becoming a compound with sodium (sodium bromide), kicking out iodine as a pure element.

Sometimes, a metal can replace another non-metal.

Fe + HCl → FeCl

! This is because Iron is more reactive than Hydrogen.

The fourth reaction is Double Displacement.

In a single displacement reaction, an element reacts with a compound. But in the double displacement reaction, a compound reacts with another compound.

The general form is:

AB + CD → AD + CB

Where A and D are cations, and C and B are anions.

There are two types of double displacement reactions:

  • Precipitation Reactions

  • Acid-base neutralization Reactions

Precipitation Reaction:

e.g Silver Nitrate + Sodium Chloride → Silver Chloride + Sodium Nitrate

AgNO3 (aq) + NaCl (aq) → AgCl(s) + Na(NO3) (aq)

Here, Ag displaces Na to become AgCl, and NO3 displaces Cl to become NaNO3.

  • Mixing two aqueous solutions and getting a solid/liquid/gas product is known as a precipitation reaction.

(aq) + (aq) = (s)

(aq) + (aq) = (aq) = No Reaction

Acid-base neutralization Reaction:

e.g HCl (aq) + NaOH (aq) → HOH (l) + NaCl (aq)

Here, H pairs up with OH to form water (which is in the liquid phase). Na pairs up with Cl, which makes NaCl (in aq phase.)

HCl (Hydrochloric Acid) is a strong acid, and NaOH (Sodium Hydroxide) is a strong base. When you mix an acid and a base, you will get water and salt.

Salt = the ionic compound formed in the acid-base neutralization reaction