1. Introduction to Chemical Reactions
Types of Chemical Reactions

2. Chemical Reactions
Matter is combined or broken apart to form a new type of matter
Bonds are broken, atoms rearranged, and new bonds are reformed
Chemical reaction is a change in which one or more substances are converted into new substances
The substances that react are called reactants
The new substances produced are called products
This relationship can be written as:
Produce
Reactants Products

3. Evidence (signs) of a Chemical Reaction
Release of a gas
Evidence - Bubbles
Change in temperature
Evidence – Temperature goes up (exothermic)
Evidence – Temperature goes down (endothermic)
Change in color
Evidence - solution changes color
Formation of a precipitate
Evidence - forms and settles to the bottom
Energy is released
Evidence - light or sound

4. Symbols Used in Chemical Reactions
Meaning of Symbol
(s)
A reactant or product in the solid state; also used to indicate a precipitate
(l)
A reactant or product in the liquid state
(g)
A reactant or product in the gaseous state
(aq)
A reactant or product in an aqueous solution (dissolved in water) →
Used to indicate the direction of a reaction. Translated as “yields” of “produces”.

5. Parts of a Chemical Equation
Reactants
Yield sign
Products
Coefficients
Subscripts
HgO(s)  Hg(l) + O2(g)
Reactants Products
“Yields”
Indicates result of reaction

6. Types of Chemical Reactions
Synthesis
Decomposition
Single Replacement
Double Replacement
Combustion

7. Synthesis Reaction Generic Form: A + B → AB Reactants: Products:
A and B are either elements or simple compounds
Products:
AB is a complex compound formed from A and B
Reaction Mechanism:
The atoms of A and B are bonded together to form a single new compound

8. Examples of Synthesis Reactions
2 Na + Cl2 → 2 NaCl
Sodium atoms and chlorine gas molecules combine to form a single new product
Sodium chloride is the product of the reaction
2 Mg + O2 → 2 MgO
Magnesium atoms and oxygen gas molecules combine to form a single new product
Magnesium oxide is the product of the reaction
In a moment, we will also see that this reaction can also be classified as a combustion reaction

9. Decomposition Reaction
Generic Form: AB → A + B
Reactants:
AB is a complex compound formed from A and B
Products:
A and B are either elements or simple compounds
Reaction Mechanism:
The compound AB breaks down into its elements or into simple compounds

10. Examples of Decomposition Reactions
2 H2O2 → 2 H2O + O2
Hydrogen peroxide molecules break down to form new products that are simple molecules
Water and oxygen gas are the products of the reaction
2 KClO3 → 2 KCl + 3 O2
Potassium chlorate molecules break down when heated to form new products that are simple molecules
Potassium chloride and oxygen gas are the products of the reaction

11. Combustion Reaction Generic Form: A + O2 → H2O + CO2 Reactants:
A is a hydrocarbon (a compound of hydrogen and carbon)
O2 is oxygen gas (we will assume more than enough oxygen is present)
Products:
When combusting a hydrocarbon, the products will always be water and carbon dioxide
Reaction Mechanism:
The hydrocarbon is oxidized and produces energy
With a hydrocarbon the reaction is generally rapid

12. Examples of Combustion Reactions
C2H O2 → 2 CO H2O
Ethene (also known as acetylene) is a hydrocarbon
When O2 is a reactant, the reaction must be combustion
The products must be water and carbon dioxide

13. Single Replacement Reaction
Generic Form: A + BY → AY + B
Reactants:
A is a metal element
BY is an ionic compound
Products:
AY is an ionic compound
B is a metal element or a diatomic molecule
Reaction Mechanism:
A and B are elements of the same type
If A is more reactive than B, the reaction occurs with A replacing B
If A is less reactive than B, no reaction can occur

14. Examples of Single Replacement Reactions
2 Al(s) CuCl2(aq) → 2 AlCl3(aq) Cu(s)
Aluminum is a metal and copper is the metal in the ionic compound
Aluminum is more reactive than copper, therefore the reaction occurs
The aluminum replaces the copper ion in the ionic compound and the element copper forms as a precipitate
What happens if the reaction is reversed?
Cu(s) + AlCl3(aq) → No reaction occurs
The copper is not more reactive than the aluminum, so no reaction occurs

15. Double Replacement Reaction
Generic Form: AX + BY → AY + BX
Reactants:
AX is an ionic compound
BY is an ionic compound
Products:
AY is an ionic compound
BX is a an ionic compound
Reaction Mechanism:
A and B are elements of the same type (both are metals ) as are X and Y (both are non-metals)
A replaces B and X replaces Y (the ions trade partners)
If an insoluble product (precipitate or insoluble gas) is produced, the reaction occurs

16. Examples of Double Replacement Reactions
Na2SO4(aq) + Ba(NO3)2(aq) → 2 NaNO3 (aq) + BaSO4(s)
The ions in the two ionic compounds change partners and form two new ionic compounds
BaSO4 is not soluble in water
BaSO4 is the product of the reaction
What happens if there is no precipitate?
Na2SO4(aq) + KNO3 (aq) → No Reaction
The ions of sodium, potassium, sulfate, and nitrate cannot produce an insoluble product
Therefore, there is no product of the reaction and that means there is no reaction between the sodium sulfate and the potassium nitrate

17. Types of Chemical Reactions Summary

18. Key Terms Combustion Reaction - A + O2 → Oxidized Metal or CO2 + H20
Decomposition Reaction -
AB → A+ B
Double replacement Reaction -
AX+ BY → AY + BX
Single replacement Reaction -
A + BY → AY + B
Synthesis Reaction -
A+ B → AB