Zero Order Reaction - Practice Questions & MCQ

In such reactions rate of reaction is independent of concentration of the reactants.
        
        
On integration we get:
  
if c = 0, t = 0 then


Example: Photo Chemical reaction.

 

Zero order reaction means that the rate of the reaction is proportional to zero power of the concentration of reactants. Consider the reaction,

At t = 0, A = A_o
At t = t, A = A
Thus, on integrating both sides, we get:

Comparing the above equation with the equation of a straight line, y = mx + c, if we plot [R] against t, we get a straight line as shown in the above figure with slope = –k and intercept equal to [R]_o.

Further simplifying the above equation, we get the rate constant, k as:

• Half-life of reaction: The half-life of a reaction is the time in which the concentration of a reactant is reduced to one half of its initial concentration. It is represented as t_1/2.
  For a zero order reaction, rate constant is given as follows:
  
  
  At t = t_1/2, [A] = [A]_o/2
  Thus, the rate constant at t_1/2 becomes:
  
  
  
  Thus, it is clear that t_1/2 for a zero order reaction is directly proportional to the initial concentration of the reactants and inversely proportional to the rate constant.
   
• Life time of Reaction: It is time in which 100% of the reaction completes. It is represented as t_lf.
  Thus, at t = t_lf, A = 0
  Now, from zero order equation, we know:
  
  
  
  
  
  

This concept can be understood by the following example:

Example: 
The reaction occurs as follows:

Initial concentration of A is given as and rate of the reaction(r) is given as k[A]^o. Find the concentration of A after time 't' and also determine the half life of A.

Solution:
For zero-order reaction, the rate equation is given as follows:

According to question, we have given:

Now, integrating both sides we get:

This is the concentration of A after time 't'.

Now, for zero-order reaction, the half-life of a reaction is given as below:

This is the half-life of A for this reaction.