Unit – I – 02

Types of Chemical Reactions (Contd.)

Depending upon the direction of the reaction:

  • Reversible Reaction:
    A chemical reaction, in which the products formed react with each other to give back the original reactants, is called a reversible reaction. conventionally the reaction proceeding from left to right is called as a forward reaction while that proceeding from right to left is called as a forward reaction.
  • Explanation:
    A   +  B   →   C   +   D    (Forward Reactions)
    C   +  D   →  A   +    B    (Backward Reaction)
    Here A & B are reactants, reacting with each other to form the products C & D. As the reaction proceeds the amounts of C & D will go on increasing and those of A and B will go on decreasing. But under the same conditions, C and D will react with each other to form A and B. Thus it is a reversible reaction. Both the reactions can be combined as
  • Types of Chemical Reactions (Contd.)
  • Characteristics of Reversible Reactions:
    1. A reversible reaction is a reaction which can proceed in both the directions, forward and backward.
    2. A reversible process is one whose direction can be reversed by an infinitesimal change in the conditions.
    3. It is a hypothetical (imaginary) reaction.
    4. It is a non-spontaneous process. It is to be arranged artificially.
    5. This process is infinitesimally slow.
    6. There is an equilibrium at every stage of the process.
    7. The direction of the process can be reversed at any stage by an infinitesimal change in one of the state functions.
    8. The driving and opposing forces differ by infinitesimally small amount.
    9. Maximum work can be obtained.
  • Irreversible Reaction:
    A chemical reaction in which the products formed do not react with each other to produce the original reactants is called an irreversible reaction.
  • Explanation:
    A   +   B   →   C   +   D
    In above example, A & B are reactants, reacting with each other to form C and D products. But under the same conditions products C and D will not react with each other to form original products. Hence only forward reaction is possible. Hence it is an irreversible reaction.
  • Examples:
    C(s)    +   O2(g)   →   CO2(g)
    H2(g) +   O2(g)   →   2H2O(l)
  • Characteristics of Irreversible Reaction:
    1. An irreversible reaction is a reaction which can proceed only in one direction. I.e. forward direction only.
    2. The irreversible process is one whose direction cannot be reversed by changing the conditions slightly.
    3. It is a natural and real process.
    4. It is a spontaneous process. it takes place naturally.
    5. This process is comparatively fast.
    6. Equilibrium is reached at the end of the process.
    7. The direction of the process cannot be reversed by small changes in state functions.
    8. The driving forces are quite larger than opposing forces.
    9. Maximum work cannot be obtained.

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