Chemical Reaction and Equation
A Chemical Reaction is a change in which one or more substances or reactants reacts to form new substances with entirely different properties.
The symbolic representation of a chemical reaction is chemical equation.
Balanced Chemical Equation
A balanced chemical equation is that in which the total number of atom of each element are equal on both sides of the equation.
Types of Reaction
1. Combination Reaction
A reaction in which two or more reactants combine to form a single product is called combination reaction.
2. Decomposition Reaction
A reaction in which a single reactant breaks down to form two or more products, is known as decomposition reaction.
2.1. Thermal Decomposition
These reactions use the energy in the form of heat for decomposition of the reactants.
2.2. Electrolysis
These reactions use the electrical energy for decomposition of the reactants.
2.3. Photolysis or Photochemical Decomposition
These reactions use light energy for decomposition of the reactants.
3. Displacement Reaction
In displacement reaction, an element displaced another element from its compound.
3.1. Double Displacement Reaction
The reaction in which two different ions or group of atoms in the reactant molecules are displaced by each other, is called double displacement reaction.
4. Oxidation Reaction
Oxidation is the process of addition of oxygen or removal of hydrogen to a substance.
5. Reduction Reaction
Reduction is the process of removal of oxygen or addition of hydrogen to a substance.
6. Redox Reaction
Those reactions in which oxidation and reduction takes place simultaneously are called redox reaction.
7. Exothermic Reaction
The reaction in which heat is released alongwith the formation of the products, are called exothermic reactions.
Respiration is an exothermic reaction.
The decomposition of vegetable matter into compost is also an exothermic reaction.
8. Endothermic Reaction
The reaction which occur by the absorption of heat/energy are called endothermic reactions.
Photosynthesis is an endothermic reaction.
Corrosion
Corrosion is the phenomenon due to which metals are slowly degraded by the reaction of air, water and chemicals present in the atmosphere.
e.g. Iron articles get coated with a reddish brown powder when left for some time. This process is commonly known as Rusting of Iron. The black coating on silver is other example of corrosion.
Prevention of Corrosion
1. By applying paint or lubricants on Iron surface.
2. By the process of Galvanization (the process of applying a protective zinc coating to iron or steel, to prevent rusting).
Rancidity
Rancidity is the process of slow oxidation of oil and fat present in the food materials resulting in the change of smell and taste in food.
Prevention of Rancidity
1. Packing of food material in air-tight containers.
2. Refrigeration at low temperature.
3. Packing of food items in packets containing nitrogen gas instead of air.
4. By adding antioxidants.