PARALLEL PATH OR CONCURRENT ELEMENTARY REACTIONS

The chemical reaction in which a substance reacts or decomposed in more than one way are called parallel or side reaction.

Some examples of parallel reactions:

PARALLEL REACTION: ILLUSTRATION TYPE (1):

Let a chemical reaction in which reactant (A) give two products (B) and (C) and both the reactions are first order reactions. Initially at t=0, pure (A) was present with concentration [A]0 and after time t concentration of (A) is [A]_t and concentration of (B) is [B]_t and concentration of (C) becomes [C]_t

[A]t -Concentration of [A] after time t:

[B]t -Concentration of [B] after time t:

[C]t -Concentration of [C] after time t:

Graphical representation of variation of conc of [A], [B], [C] with time: If K₁>>> K₂ then [B] is the main product and [C] is the side product

Ratio of concentration of (A) and (C) After time t is:

Percentage Yield of Product:

Time of completion and half life of reactant:

Question for Illustration (1):  Cu⁶⁴ (Half life=22.8 hours) decay by beta emission (38%), beta+ emission (19%) and electron capture (43%). write the decay product and calculate Half lives for each of the decay process. [IIT 2002]

Solution:

(1):

 (2)  Above are parallel reactions occurring from Cu⁶⁴   

T₁ T₂ and T₃ are the corresponding partial half lives and also K= K₁ + K₂ + K₃ (for parallel reaction) 

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