Chemical reactions and equations
Whenever a chemical change occurs, we can say that a chemical reaction has taken place. Any of the following observations helps us to
determine whether a chemical reaction has taken place - change in state, change in colour, evolution of a gas or change in temperature. The
substances that undergo chemical change in the reaction are the reactants. The new substance is formed during the reaction as a product. A
chemical equation represents a chemical reaction. The gaseous, liquid, aqueous and solid states of reactants and products are represented by
the notations (g), (l), (aq) and (s), respectively. Sometimes, the reaction conditions such as temperature, pressure, catalyst, etc., for the reaction
are indicated above and / or below the arrow in the equation. When two or more substances (elements or compounds) combine to form a
single product, the reactions are called Combination dreactions. The reactions in which a single reactant breaks down to give simpler products
are called Decomposition Reaction. Reactions in which one elements displace or remove another element are called Displacement reactions.
Such reactions in which there is an exchange of ions between the reactants are called Double Displacement reactions. In some reactions, one
reactant gets oxidised while the other gets reduced, such reactions are called oxidation reduction reactions or redox reactions. Reactions in
which, heat is released along with the formation of products are called exothermic chemical reactions. Reactions in which energy is absorved
are known as endothermic reactions. In some reactions, a substance gains oxygen or loses hydrogen, it is oxidised. If a substance loses oxygen
or gains hydrogen during a reaction, it is reduced. When a metal is attacked by substances around it such as moisture, acids, etc., it is said to
corrode and this process is called corrosion. When fats and oils are oxidised, they become rancid and their smell and taste change. To keep
foods containing fats and oil fresh, substances which prevent oxidation (antioxidants) are added to it.
Whenever a chemical change occurs, we can say that a chemical reaction has taken place. Any of the following observations helps us to
determine whether a chemical reaction has taken place - change in state, change in colour, evolution of a gas or change in temperature. The
substances that undergo chemical change in the reaction are the reactants. The new substance is formed during the reaction as a product. A
chemical equation represents a chemical reaction. The gaseous, liquid, aqueous and solid states of reactants and products are represented by
the notations (g), (l), (aq) and (s), respectively. Sometimes, the reaction conditions such as temperature, pressure, catalyst, etc., for the reaction
are indicated above and / or below the arrow in the equation. When two or more substances (elements or compounds) combine to form a
single product, the reactions are called Combination dreactions. The reactions in which a single reactant breaks down to give simpler products
are called Decomposition Reaction. Reactions in which one elements displace or remove another element are called Displacement reactions.
Such reactions in which there is an exchange of ions between the reactants are called Double Displacement reactions. In some reactions, one
reactant gets oxidised while the other gets reduced, such reactions are called oxidation reduction reactions or redox reactions. Reactions in
which, heat is released along with the formation of products are called exothermic chemical reactions. Reactions in which energy is absorved
are known as endothermic reactions. In some reactions, a substance gains oxygen or loses hydrogen, it is oxidised. If a substance loses oxygen
or gains hydrogen during a reaction, it is reduced. When a metal is attacked by substances around it such as moisture, acids, etc., it is said to
corrode and this process is called corrosion. When fats and oils are oxidised, they become rancid and their smell and taste change. To keep
foods containing fats and oil fresh, substances which prevent oxidation (antioxidants) are added to it.
