Physical and Chemical Changes – Physical and Chemical Changes
* Change is all around us and happening constantly. Some changes are Physical and some are chemical.
* Some changes affect only the physical properties of the substance that is undergoing change. Physical include things like shape, size, colour and state of matter. Physical changes are generally reversible.
* No new substances are formed when a physical change takes place.
* Some changes are the result of chemical reaction. These lead to the creation of new substances and generally cannot be reversed.
* Chemical changes are sometimes accompanied by things like heat, sound, smell, formation of a gas, etc.
Chemical Reactions and Equations – Types of Chemical Reactions
The Important types of chemicals reactions are:
* Combination: A combination reaction has multiple reactants, but only one product.
* Decomposition: A decomposition reaction always has one reactant and many products.
* Decomposition can occur as a result of the action of heat, electricity or light energy.
* Single displacement: In a single displacement reaction, one of the reactants is always an element.
* Acid- base or neutralization: In an acid- base reaction, one of the product is always water.
* Double displacement: Where the two reactants are compounds, the reaction involves double displacement.
* Combustion: A combustion reaction cannot occur without oxygen.
* Oxidation: An oxidation reaction involves the addition of oxygen or the removal of hydrogen from a substance.
* Reduction: A reduction reaction involves the addition of hydrogen or the removal of oxygen from a substance.
* Oxidation and reduction reactions together are known as redox reactions.
* Decomposition reactions are the opposite of combination reactions.
Based on whether energy is released or absorbed, a reaction can be of two types:
* Endothermic: Chemical reactions in which energy is absorbed.
* Exothermic: Chemical reactions in which energy is released.