9+ Zero Order Reaction Example: Detailed Explanations

The zero order reaction example means a type of reaction where changing the concentration of species reacting will not have an effect on the rate of reaction. Here we will have a closer approach towards the concept of zero order reaction examples

Zero order reaction examples:

1)Photochemical Reaction

H2(g) + Cl2 (g) →  2HCl ( in presence of hv)

It is a type of reaction that is being carried out between the species hydrogen along with chlorine.

It has been observed that almost all the photochemical type of reactions are zero order reaction examples. The study of this reaction is made by keeping the hydrogen (H2) and the element chlorine ( note that both are gases) over the water. So the rate is calculated as the dissociation of hydrogen chloride Occurs as the water is raised in the vessel.

2)Decomposition reaction ( nitrous oxide)

2N2O(g) → 2N2 (g) + O2  ( in presence of hot platinum and quite a high pressure)

The decomposition reaction carried out of nitrous oxide over the surface of element like platinum (hot).

So in this reaction the N2O is decomposed to nitrogen and oxygen, the reaction is carried out at a high temperature and the pressure also kept high. So the concentration of the reactant has no role in the rate of the reaction.

3) Decomposition reaction ( ammonia )

2NH3 (g) → N2 (g) + 3H2 (g) ( in presence of molybdenum or tungsten along with high pressure)

The reaction of decomposition of ammonia (NH3) in the presence of elements that of molybdenum or even tungsten can be used.

In this reaction NH3 decomposes to give nitrogen and hydrogen. When molybdenum is used in the reaction, for preparing ammonia it is called Haber’s process.

4) Dissociation reaction ( Hydrogen iodide)

2HI (g) → H2(g) + I2 (g) ( in presence of Au and high pressure)

The dissociation type of reaction like the dissociation of HI (hydrogen iodide) on the surface of element like gold (at quite a high pressure).

In this reaction dissociation of HI occurs at a temperature of around 150 degrees Celsius and concentration of HI does not affects rate of the reaction.

5) Decomposition reaction ( oxalic acid)

C2H2O4  → CO + CO2 + H2O ( in presence of sulfuric acid and heat )

The decomposition reaction of acid like oxalic acid is said to be zero order reaction example.

So in this decomposition reaction the concentration of oxalic acid the reactant will have no role to play in determining the rate of the decomposition reaction.

6)Chlorination ( alkanes )

CH4  + Cl2  → CH3Cl + HCl ( in presence of sunlight)

The reaction of chlorination like that is carried out on alkanes in the presence of (necessary) light (sunlight).

This reaction is a zero order reaction example and a free radical type of reaction.

7) Iodination reaction ( Acetone )

CH3COCH3  + I2  → ICH2COCH3 + HI 

The reaction of iodination which is carried out on the acetone.

This iodination reaction is usually used to study the kinetics. The progress of this reaction can be understood by observing the decrease of the concentration of iodine.

8)Enzymatic ( maltase, catalase and transferases )

All the enzymatic reactions are said to be of the order zero.

Some examples of such reactions have been mentioned below.

a)Reaction of maltose to glucose by maltase.

C12H22O5  →  C6H12O6  +  C6H12O6  (in presence of maltase)

b)Reaction of hydrogen peroxide to water and oxygen in the presence of catalyst catalase

2H2O2  → 2H2O + O2

c) Group transfer reaction by the enzyme transferases.

9)Alanine + Oxaloacetate  → Pyruvate + Aspartate

Third order reaction example

This kind of reaction is where the rate of the particular reaction is said to be proportional to the concentration of the molecules reacting (each one). So the determination of rate is done by varying the concentration terms (3). In other words the number of molecules required for this kind of reaction should be at least 3 (minimum).

There are 3 special cases of the third order reaction:

  • When all the concentration involved in the reaction are same or we can say they are equal.
  • When the concentration of two reacting species same meaning equal concentration and the third one is different in concentration.
  • When all the concentration involved in the reaction are all different.

Important point to be noted about third order reaction:

We determine the reaction order by taking into consideration the slowest step of the reaction.

Examples of third order reaction:

1) The reaction of nitric oxide and chlorine is said to be a third order reaction.

2Cl2 + 2NO → 2NOCl

2) The reaction of nitric oxide with the oxygen.

2NO + O2 → 2NO2

3)The reaction of ferric chloride with potassium iodide follows the third order reaction.

FeCl3 + KI → FeCl2 + KCl + I2

Pseudo first order reaction example:

What  we mean by a pseudo first order reaction is the order of a particular reaction is in reality greater than one but it appears to be 1. This can be done by bringing a change in the concentration (either by increasing the concentration or by decreasing it).

Example of pseudo first order reaction:

1) Hydrolysis reaction of ethyl acetate.

2) The inversion reaction of the sugar (cane).

Negative order reaction example:

This kind of reaction is where when the concentration of the reacting species or the product is increased the rate of the reaction is decreased.

Below is the example of such kind of reaction.

2O3  → 3O2

Here the order is negative one.

Now we will see the integrated rate law:

Consider the reaction taking place:

A → Product

Where the rate (r) = [A]0

This symbolizes that rate of the reaction will be zero.

Let the initial concentration at t = 0 be, A = 0

And the final or the remaining concentration at t = t , A = A

zero order reaction example
zero order reaction example

A= indicates the initial concentration of A

A = indicates the concentration of A at any time t (remaining)

R = indicates the rate constant

t = indicates the time in which concentration changes from A0 to A

Now let’s see the graph : concentration of A ( at any time) v/s time

A = -Kt + A

is of the type y = mx + c

So the concentration of A v/s time is a straight line graph with a negative slope for zero order reaction.

Half life reaction

The meaning of this term is the time in which a particular reaction completes 50% at t = t1/2, the remaining concentration A = A0/2

A = A0 – At

A0/2 = A0  – Kt1/2

Kt1/2 = A0/2                             

t1/2 = A0/2K


A0 = the initial concentration and K = the rate constant

This equation is valid only for A → Product.

Life time of reaction

This term means that the time in which 100% reaction completes at t= tef remaining concentration A = 0

A = A0 – At

0 = A– Ktef

tef = A0/2

Some characteristics of the zero order reaction:

We call a reaction a zero order reaction when the power of concentration is equivalent to zero.

In the reaction the concentration of reactant will decrease (linearly) with the time.

The time which is required for a particular reaction to go to completion is given by dividing the quantity initial concentration by the rate constant.


To wrap the post, we can conclude that in a zero order reaction the concentration of the reactant has no role to play in determining the rate of the reaction. And most of the enzymatic reactions follow zero order kinetics.

Sania Jakati

This is Sania Jakati from Goa. I am an aspiring chemist pursuing my post graduation in organic chemistry. I believe education is the key element that moulds you into a great human being both mentally and physically. I'm glad to be a member of scintillating branch of chemistry and will try my best to contribute whatever I can from my side and Lambdageeks is the best platform where I can share as well as gain knowledge at the same time. LinkedIn-https://www.linkedin.com/in/sania-jakati-0954101bb

Recent Posts