| Reversible and irreversible reactions |
| Reactants, written on the left hand side of a chemical equation, proceed in their reactions. The products are written on the right hand side of the chemical equation. This is indicated by the direction of the arrow in a chemical equation. This is a direct reaction. |
| For example when steam is passed over hot iron, hydrogen gas and ferroso-ferric oxide |
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| As soon as the products are formed they begin to react among themselves and actually a backward or reverse reaction starts. |
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| It is interesting to note that if carried out in open vessel, the reaction cannot go in the backward direction because, one of the products of the reaction, the hydrogen gas escapes. But if the reaction is carried out in a closed vessel, the reaction becomes reversible, because when hydrogen gas is passed over hot ferroso-ferric oxide, steam and iron are produced. |
| These two reactions may be represented by a single equation as |
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| Thus a chemical reaction that proceeds in one direction only is known as an irreversible chemical reaction. A chemical reaction in which substances react together to produce resultants and the resultants in turn react with one another to produce the original substances is known as reversible chemical reaction. |
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