Introduction to classifying types of chemical reactions

Why classify chemical reactions?

• There are so many chemical reactions that occur daily in living things, laboratories, and industry. • Classifying the different types of reactions helps keep them organized

and easier to understand.

• Think like a library; so many books, they need to be classified into categories like fiction,non-fiction,biographies,etc.• Same thing goes with chemical reactions

Scientists classify reactions into 5 types• Synthesis A + B AB

• Combustion A + O2 heat + H2 O + AO2

• Decomposition AB A + B

• Single-replacement A + BX AX + B

• Double-replacement AX + BY AY + BX

Synthesis Reactions

• Two elements combine to produce one new compound.

• Example synthesis reaction:• Iron combines with chlorine gas to produce iron(III) chloride.

• 2 Fe(s) + 3 Cl2(g) 2FeCl3 (s)

Synthesis reaction continued…

• Just as 2 elements can combine, 2 compounds can also combine to form one compound. This is also classified as a synthesis reaction.

• Example: calcium oxide reacts with water to form calcium hydroxide• CaO(s) + H2O(l) Ca(OH)2 (s)

Combustion Reactions

• Oxygen combines with a substance and releases energy in the form of heat and light.

• Oxygen can combine with many different substances, making combustion reactions a common occurrence.

• Some combustion reactions are also synthesis reactions; but not all combustion reactions are synthesis reactions.

Combustion reactions continued….

• The reaction involving methane gas , CH4, and oxygen illustrates a combustion reaction in which one substance replaces another in the formation of the products. This is NOT a synthesis reaction.

• CH4(g) + 2O2(g) CO2(g) + 2H2O(g)

Decomposition Reactions

• Opposite of synthesis reactions

• A single compound breaks down into two or more elements or new compounds. These reactions require an energy source, such as heat, light, or electricity.

• Example: ammonium nitrate breaks down into dinitrogen monoxide and water when the reactant is heated to high temperature• NH4NO3(s) N2O(g) + 2H2O(g)