Types of Chemical Reactions

1. Synthesis Reactions

A+B ¡ú AB

1) When both A and B are elements;

e.g. 2 Na (s) + Cl₂ (g) ¡ú 2 NaCl (s)

       When Iron Rusts, 4 Fe (s) + 3 O₂ (g) ¡ú 2 Fe₂O₃ (s)

2) When both A and B are compounds; 

Two compounds can also combine to form one product.

2 SO₂ (g) + O₂ (g) ¡ú 2 SO₃ (g)

3) When the reaction is between a compound and an element.

2. Combustion Reactions

The conditions for combustion:

(1) Something flammable;

(2) At the right temperature to ignite;

(3) Mixed with fresh air (oxygen).

There are two characteristic features of combustion reactions:

(1) Reactants include oxygen;

(2) Release a large amount of energy in the form of heat and light.

e.g. 2 H₂ (g) + O₂ (g) ¡ú 2 H₂O (l)

Hydrocarbon

(1) An organic compound consisting entirely of hydrogen and carbon;

(2) When burning in oxygen, it generates carbon dioxide and water.

3. Decomposition Reactions

AB ¡ú A + B

A or B can not only be element, but also be new compound.

e.g. CaCO₃ (s) ¡ú CaO (s) + CO₂ (g)

Decomposition reactions often require energy. However, not all decomposition reactions are endothermic reactions.

e.g. 2 NaN₃ (s) ¡ú 2 Na (s) + 3 N₂ (g)

4. Replacement Reactions

(1) Single-replacement Reactions

A + BX ¡ú AX + B

A. Between metal and hydrogen atom

e.g. 2 Li (s) + 2 H₂O (l) ¡ú 2 LiOH (aq) + H₂ (g)

B. Between metal and another metal atom

Metal Reactivity Series

A specific metal can replace any metal atom in a compound listed below it, while it cannot replace the ones listed above it.

e.g. Cu (s) + 2 AgNO₃ (aq) ¡ú 2 Ag (s) + Cu(NO₃)₂ (aq)

3. Between nonmetal and another nonmetal atom

(2) Double-replacement Reactions

AX + BY ¡ú AY + BX

A & B : cation (positively charged ion)

X & Y : anion (negatively charged ion)

e.g. 2 NaOH (aq) + CuCl₂ (aq) ¡ú 2 NaCl (aq) + Cu(OH)₂ (s)

ALL double-replacement reactions produce at least one of water, a precipitate, or a gas.

Products of Double-replacement Reactions

1. Write the components of the reactions in a skeleton equation;

2. Identify the cation and the anion in each compound;

3. Pair up each cation with the anion from the other compound;

4. Write the formulas for the products using the pairs from Step 3;

5. Write the complete equation for the double-replacement reaction;

6. Balance the equation.