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Chemical equations and reactions Cheat Sheet by

Chemical Reaction

Whenever a chemical change occurs we can say that
a chemical reaction has taken place
eg 1. Food gets digested in our body
2. Rusting of iron.

Balancing Equation

We balance the chemical equation so that no. of
atoms of each element involved in the reaction remain same at the reactant
and product side.
eg Fe + H2O → Fe2O3+ H2
can be written as
3 Fe(s) + 4H2O(g) → Fe2O3(s) +4H2(g)

Combin­ation Reaction

The reaction in which two or more substances
combine to form a new single substance
eg CaO(s) + H2O(l) → Ca(OH)2 (aq)
Calcium Water Calcium hydroxide oxide (slaked lime)

Displa­cement Reaction

The chemical Reaction in which an element displaces another element from its solution


Oxidation is the gain of oxygen or loss of hydrogen

Exothermic Reactions

Reaction in which heat is released along with the
formation of products
– Respir­ation is also exothermic reaction.
– Decomp­osition of vegetable matter into compost.

Decomp­ositon Reactions

The reaction in which a single substance decomposes to give two or more substa­nces.

Double Displa­cement Reaction

The reaction in which two different atoms or group of atoms are mutually exchanged

Precip­itation Reaction

Any reaction that produces a precip­itate is called a precip­itation reaction.


Reduction is the loss of oxygen or gain of hydrogen.

Chemical Equation

A chemical reaction can be expressed symbol­ically
by using chemical equation
eg: magnesium is burnt into air to form magnesium oxide can be repres­ented
Mg + O2 → MgO
– We can observe or recognise a chemical reaction by observing change
in state, colour, by evolution of gas or by change in temper­ature.
Physical state of the reactant and products are mentioned to make chemical
reaction more inform­ative. eg: we use (g) for gas, (l) for liquid, (s) for solid
and (aq) for aqueous.

Endoth­ermic Reactions

The reactions which require energy in the form of heat, light or electricty are called Endoth­ermic Reactions
2Ba(OH)2+ NH4Cl → 2BaCl2+ NH4OH

Redox Reaction

The reaction in which one reactant gets oxidised while other gets reduced


When a metal is attacked by substances around it such as moisture, acids etc.
eg. Reddish brown coating on iron.
(ii) Black coating on Silver


When fats and oils are oxidised they become rancid and their smell and taste change.
Antiox­idants are added to foods containing fats and oil.

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