Unit 4: Reactions and Stoichiometry

Unit 4: Reactions and Stoichiometry

Content Outline: Types of Chemical Reactions (4.2) – Part 1

I.  There exist 5 basic types of chemical reactions:

A)  Synthesis – “putting together to make”.

B)  Decomposition – “breaking apart into simpler components”.

C)  Combustion – “burning in the presence of Oxygen gas”.

D)  Single Replacement – “swapping elements”.

E)  Double Replacement – “mutual exchange of elements”.

II.  Synthesis Reactions (“putting together to make”)

A.  This reaction takes two or more simple substances and combines them to form a new compound.

B.  The basic chemical reaction:

A + B à AB

For example: 2Mg(s) + O2(g) à 2MgO(s)

C.  Synthesis reactions with Oxygen gas

1.  Produces “oxides”. (As seen above.)

2.  Remember, the transition metals (Group “d”) can produce more than one “oxide” compounds.

For example: a) 2 Fe(s) + O2 à 2FeO(s)

b) 4 Fe(s) + 3O2(g) à 2Fe2O3(s)

D. Synthesis reactions with Sulfur.

1. Produces “sulfides”.

For example: Mg(s) + S(s) à MgS(s)

E. Synthesis reaction with Group 1 metal and a halogen (Group 17).

1. Remember, halogens for diatomic molecules, so it is M + X2 à MX.

For example: 2Li(s) + Cl2(g) à 2LiCl(s)

F. Synthesis reaction with Group II metal and a halogen (Group 17).

1. These do balance automatically, so it is M + X2 à MX2.

For example: Ca(s) + Cl2(g) à CaCl2(s)

G. Synthesis reaction with a metal oxide.

1. Metallic oxide reacts with water to form metallic Hydroxides (OH)1-so: MO +H2O à M(OH).

For example: MgO(s) + H2O(l) à Mg(OH)2(s)

H. Synthesis reaction with a non-metal oxide.

1. Non-metallic oxide reacts with water to form Oxyacids so: NMO + H20 à HNMO(aq).

For example: SO2(g) + H2O(l) à H2SO3(aq)

2. H2SO3 is a source of acid rain from burning fossil fuels, such as gasoline or diesel.

III.  Decomposition Reactions (“breaking apart into simpler components”)

A.  A single compound undergoes a reaction that produces two or more simpler substances.

B.  The basic chemical reaction:

AB à A + B

C.  Most decomposition reactions require heat or electricity be added to start or activate the chemical reaction.

1.  If using electricity to power the decomposition, it is referred to as electrolysis. (“Lysis” means “to split”.)

D.  Decomposition of metal carbonates:

1. Produces a metal oxide and CO2(g)

For example: MgCO3(s) à MgO(s) + CO2(g)

E.  Decomposition of Metal hydroxides (Bases):

1. Produces a Metal oxide and H2O(l) If the metal has an oxidation number other than two, equation requires balancing.

For example: Mg(OH)2(s) à MgO(s) + H2O(l)

If the metal has an oxidation number other than two, equation requires balancing.

For example: 2Na(OH)(s) à Na2O(s) + H2O(l)

F.  Decomposition of metal chlorate:

1.  Produces a metal chloride and Oxygen gas (O2).

For example: 2KClO3 à 2KCl(s) + 3O2(g)

G.  Decomposition of an Acid:

1.  Produces a non-metal oxide and water.

For example: H2CO3(aq) à CO2(g) + H2O(l)

2.  The example above takes place in your body to help maintain the proper pH of your blood.

IV.  Combustion Reactions (“burning in the presence of Oxygen gas”)

A.  A substance combines with Oxygen gas and releases a large amount of energy in the form of light and heat. (Like striking a match.)

B.  Produces CO2(g) and H2O(g) when burning organic substances. (A complete combustion occurs.)

For example: Natural gas (C3H8(g)) + 5O2(g) à 3CO2(g) + 4H2O(g) + Heat