Types of Chemical Reactions

Good News!

Of all the millions of possible chemical reactions, there are only

5 basic types of reactions

Synthesis

Two or more reactants combine to form a product:

A + B C

C + O2 CO2

Decomposition

The reverse of synthesis: A compound breaks down into two or more simpler substances

A B + C

CO2 C + O2

Single Replacement

A “single” element replaces another element in a compound

A + BX B + AX

Na + AgNO3 Ag + NaNO3

When will single replacement reactions occur?

Use Table J for single replacement reactions

The higher the element is on the table, the more reactive it is. A reactive element wants to react, and form a compound. It will “bump” a less reactive element out of the compound and take its place.

Single Replacement

In this example, Na is more reactive than Ag, so Na bumps Ag out of the nitrate compound and takes its place.

Na + AgNO3 Ag + NaNO3

Double Replacement

Two aqueous ionic compounds (dissolved in water) switch positive ions to produce either a precipitate, a gas, or a molecular compound (like water)

AB + CD AD + CBAgNO3(aq)+ NaCl(aq) AgCl(s) + NaNO3(aq)

Double Replacement

Use Table F to determine if a precipitate will form

AB + CD AD + CBAgNO3(aq)+ NaCl(aq) AgCl(s) + NaNO3(aq)

Combustion

Hydrocarbon and oxygen yields carbon dioxideand water and heat

CH4 + O2 CO2 + H2O + heat

Balancing Equations

Mass is always conserved in a chemical reaction

N + O NO

N + O2 NO2

H2 + O2 H2O

Is mass conserved in this equation?

NO!

Reactants:

2 H2 O

Products:

2 H1 O

H2 + O2 H2O

How to Balance an equation

Step 1. Place a box around all compounds

Step 2. DO NOT make any changes to the compounds inside each box!!!!!!

H2 + O2 H2O

Reactants:

2 H2 O

Products:

4 H2 O

How to Balance an equation

Step 3. Place coefficients in front of eachbox to show conservation of mass. Everything inside the box will be multipliedby this number.

2

H2 + O2 H2O

Reactants:

4 H2 O

Products:

4 H2 O

How to Balance an equation

Step 3. Place coefficients in front of eachbox to show conservation of mass. Everything inside the box will be multipliedby this number.

22

H2 + O2 H2O

Reactants:

4 H2 O

Products:

4 H2 O

How to Balance an equation

Step 4. Count the types of atoms on bothsides of the equation. The atoms on the reactantside must be the same as the atoms on theproduct side

22

=

Helpful Hints for balancing

1) Balance one type of atom at a time

2) Balance atoms that appear only once on each side of the equation first

3) Balance oxygen and hydrogen last

4) It is an iterative process. Be Patient!

Balance these….

Fe + O2 Fe2O3

Mg + HCl H2 + MgCl2

Unknown reactants or products

Since mass is always conserved, this principle can be used to find unknown parts of a chemical reaction

Count the atoms on both sides of the equation and determine what atoms are missing from one side……

Unknown reactants or products

2 Na + 2H2O X + 2NaOH

Reactants: Products:

2 Na4 H2 O

2 Na2 H2 O

X must be H2

Unknown reactants or products

2 Na + 2H2O H2 + 2NaOH

Reactants: Products:

2 Na4 H2 O

2 Na2 H2 O

X must be H2

Finding Missing Mass

In a similar way to finding missing compounds, missing mass can also be found since mass is always conserved.

Given the following balanced equation:

2 KClO3 2KCl + 3O2

If 103 g of KClO3 decomposed to form 62.7 g of KCl,how many grams of oxygen gas are formed?

2 KClO3 2KCl + 3O2

103 g = 62.7 g + x

103 g – 62.7 g = x

40.3 g = x