CHEMICAL REACTIONS AND EQUATIONS
Chemical reactions→are the process in which new substances with new properties are formed
Reactants→substances which takes part in a chemical reaction
Product →new substances produced as a result of chemical reaction
Chemical changes are often identified by: ★Change in state, color, or temperature. ★Evolution of
gas or formation of a precipitate.
Chemical equation→symbolic representation of chemical reaction which gives more information
about reaction
Mg(magnesium)(s) + O2(oxygen)(g) →MgO(s)
Balancing Chemical Equations
Why balance?
Equations must be balanced to satisfy the Law of Conservation of Mass (mass cannot be created or
destroyed).
This requires an equal number of atoms for each element on both sides of the equation.
A2(g) + B2(g)→2AB(g)
Types of chemical reaction :
1. Combination Reaction→Two or more substances combine to form a single product.
General Form: A+B→ AB
Example: Burning of coal. C(s)+O2(g)→ CO2(g)
2. Decomposition Reaction→A single reactant breaks down into two or more simpler products. This
usually requires energy in the form of heat, light, or electricity.
General Form: (AB→ A+B)
Three types:
Thermal decomposition- due to heat energy Example: Heating calcium carbonate(limestone).
CaCO3(s) → CaO(s) + CO2(g)
Electrolytic Decomposition- due to electrical energy Example:
Electrolysis of water to yield hydrogen and oxygen gases. 2H2O(l) → 2H2(g) +
O2(g)
Photolytic Decomposition-due to light energy. Example: Decomposition of silver chloride, which
turns grey in sunlight as it breaks down into silver metal and chlorine gas. 2AgCl(s) → 2Ag(s)
+ Cl2(g)
Chemical reactions→are the process in which new substances with new properties are formed
Reactants→substances which takes part in a chemical reaction
Product →new substances produced as a result of chemical reaction
Chemical changes are often identified by: ★Change in state, color, or temperature. ★Evolution of
gas or formation of a precipitate.
Chemical equation→symbolic representation of chemical reaction which gives more information
about reaction
Mg(magnesium)(s) + O2(oxygen)(g) →MgO(s)
Balancing Chemical Equations
Why balance?
Equations must be balanced to satisfy the Law of Conservation of Mass (mass cannot be created or
destroyed).
This requires an equal number of atoms for each element on both sides of the equation.
A2(g) + B2(g)→2AB(g)
Types of chemical reaction :
1. Combination Reaction→Two or more substances combine to form a single product.
General Form: A+B→ AB
Example: Burning of coal. C(s)+O2(g)→ CO2(g)
2. Decomposition Reaction→A single reactant breaks down into two or more simpler products. This
usually requires energy in the form of heat, light, or electricity.
General Form: (AB→ A+B)
Three types:
Thermal decomposition- due to heat energy Example: Heating calcium carbonate(limestone).
CaCO3(s) → CaO(s) + CO2(g)
Electrolytic Decomposition- due to electrical energy Example:
Electrolysis of water to yield hydrogen and oxygen gases. 2H2O(l) → 2H2(g) +
O2(g)
Photolytic Decomposition-due to light energy. Example: Decomposition of silver chloride, which
turns grey in sunlight as it breaks down into silver metal and chlorine gas. 2AgCl(s) → 2Ag(s)
+ Cl2(g)
