What is change?
Well in chemistry, change can be explained on physical grounds. Changes are very random or uncertain phenomena, it can be better or worse depending on your view. Every day we see different objects changing around us like melting of ice, cooking of food etc. In some cases, you get back the original substance and in some, you won’t get it back. Some changes are slow while some are fast, some are natural and some are man-made. You will find that many changes are taking place around us for e.g. growing of plants in your balcony, sometimes there is a change in colour and sometimes you will find drying of leaves.
Any changes which can be reversed or are a temporary conversion are known as reversible changes. The reactions which are reversible are called reversible reactions. In this reaction, one substance is modified into another form but a new compound is not formed. Processes such as melting, boiling, evaporation, freezing, condensation, dissolution are reversible changes. Few examples are melting of wax, freezing of ice, boiling water which evaporates as steam and condenses back to water.
Reactions are an interaction of two or more compounds called reactants to produce a product(s). In a reversible reaction, reactants and products formed are connected by a two-way arrow (⇌). This means reactants can be obtained back from the products.
Consider the reaction below,
A +B ⇌ C + D
Here, A and B are two reactants which react to give C and D. The two-headed arrow indicates that reaction is reversible and the reactants, A and B can be obtained from C and D.
In contrast to reversible changes, irreversible changes are permanent changes. Reactants react to form an entirely new compound and cannot be reversed. Heating, burning, mixing, powdering are few processes which cause irreversible changes. A common observable example is the cooking of raw egg which can’t be converted back to its original form. Ash obtained by the combustion of paper or any other substances is another example.
When a reaction is taking place in a unidirectional way such reactions are called irreversible reactions. In such reactions in a period of time reactants react completely to form a product. Here reaction is denoted by a one-way arrow (→).
A → B +C
Here, A is the reactant which is completely converted into products B and C which do not react to form A.
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