Classification of Chemical Reaction

We know that what is Chemical reaction and what happened when a chemical reaction occurs. Now we understand about the Classification of reaction on different basis. 

Classification of Chemical Reaction -
(1)Based On The Physical State of The Substance Present
(A)Homogeneous reaction
A homogeneous reaction is defined as a reaction in which all reactants and products are in a single phase except solid phase. (either in a gas or liquid phase)  
For example- synthesis of ammonia in which all reactants ( N₂ and H₂ ) and products ( NH₃) are in gas phase.  
(B)Nonhomogeneous reaction
A non-homogeneous or heterogeneous reaction is defined as a reaction in which products and reactants are in different phases.(like if one reactant is in gas phase than the other reactant is in liquid phase and the product is in solid phase) 
For example - 
        Mg + 2HCl ➝  Mg-Cl₂ + H₂

(2)Based On The Forward And Backward Path
(A)Reversible reaction
A reversible reaction define as a reaction in which reactants are converted into products and products are converted into reactant simultaneously. That means, a reversible reaction proceeds in both the direction (forward and backward path). For example-
                CaO + CO₂ ⇋ CaCO₃
                  N₂ + 3H₂ ⇋ 2NH₃
(B)Irreversible reaction
A reaction is called as an irreversible reaction if only reactants are converted into products (conversion of product into reactant is not possible). That means, an irreversible reaction proceeds in one direction only.
( forward path only or no backward path) 
For example -    
                      C + O₂ ➞ CO₂
        Ag-NO₃ + Na-Cl ➞ Ag-Cl + NaNO₃

(3)Based On Step Involved
(A)Elementary reactions
An elementary reaction is define as a reaction in which the products are formed by the original reactants in a single elementary step. It has a single transition state (no intermediates formed). In this type of reaction, the observed rates law and the experimental rates law,both are identical. 
"Reaction in which the rate equation corresponds to a stoichiometric equation are called elementary reactions."
For example- 
   C₂H₅OH + CH₃-COOH ➝ CH₃COO-C₂H₅ + H₂O  
            2NO + O₂ ➝ 2NO₂
(B)Nonelementry reaction 
A reaction in which the products are formed from the reactants through a series of elementary steps, is called as non-elementry reaction. In this type of reaction, the observed rate and the experimental rates are not identical. It involves intermediate formation with a transition states.(one intermediates is formed between two transition states ) For example-
         2HBr + O₂ ➝ H₂O₂ + Br₂
The above reaction is proceed in three different elementary step-
         Step 1- H-Br + O2 ➝ HO₂Br
         Step 2- HO₂Br + H-Br ➝ 2HOBr
         Step 3- 2HOBr ➝ H₂O₂ + Br₂
▶"A comparation of the stoichiometric equation with the experimental expression can suggest whether the reaction is elementary or not. That means if both are identical then the reaction is elementary otherwise non-elementary".
Generally, a chemical reaction rarely proceed in a single step.

(4)Based On Catalyst Present
(A)Catalytic reaction /Catalysis
A reaction in which a catalyst is used to alter the rate of chemical reaction, is known as a catalytic reaction. A catalyst is a substance which is added to the reaction to increase the rate of reaction without getting consumed during the reaction and this phenomenon is known as a catalysis.  According to the phase of the reactant, product and catalyst, these reactions are further categorize into two types of reaction and these are- homogeneous catalytic reaction (all are in a single phase or in same phase) and heterogeneous catalytic reaction (all reactants in different phases). 
For example -
        2SO₂ + O₂  + NO(as catalyst) ➝ 2SO₃
(B)Non-catalytic reaction
A chemical reaction which is completed and forming new product without using any influencing material (catalyst) is called as non-catalytic reaction.  It can also be divided into two type based on phases present like homogeneous and non-homogeneous reaction. 
For example-
                 CaCO₃  ➝   CaO + CO₂
                 H₂ + Br₂  ➝   2HBr

Difference between these reactions types
(1) Difference between Homogeneous and non-homogeneous /Heterogeneous reactions
  • Homogeneous reactions are those reactions in which all the reactants and products are in same phase while Non-homogeneous reactions are those reactions in which reactants and products are in different phase.
  • Homogeneous reactions have more  uniformity than heterogeneous reactions.
  • Homogeneous reactions are simple while heterogeneous reactions are complex in nature.
  • Since, there is only one phase in homogeneous reactions therefore homogeneous reactions depends only on the nature of interaction between reactants whereas heterogeneous reactions depends on both the phase of matter and the interaction between reactants.
  • N₂(g) +3H₂(g) ➝ 2NH₃(g)  ➤ Homogeneous Mg(s) + HCl(l) ➝ Mg-Cl₂(aq) + H₂(g)  ➤Heterogeneous
(2)Difference between reversible and irreversible reactions
  • Reversible reactions are those reactions in which reactants can be converted into products and products back to reactants whereas irreversible reactions are those reactions in which reactants can be converted into products but products can't be convert back into reactants.
  • Reversible reactions can achieve equilibrium but irreversible reactions can not.
  • Reversible reactions proceed in both the directions whereas irreversible reactions proceed only in forward direction.
  • Reversible reactions operate in both directions while irreversible reactions operate in only one direction. 
  • Reversible reactions are relatively slow while irreversible reactions occur at a faster rate.
  • In reversible reactions, the reactants can't be completely converted into products while in irreversible reactions, the reactants can be completely converted into products.

(3)Difference between elementary and non-elementary reactions
  • Elementary reactions occur in a single steps while non-elementary reactions occur in more than one steps or multiple steps.
  • Elementary reactions have only one transition state while non-elementary reactions have more than one transition states.
  • Intermediate can not be detected in elementary reactions while non-elementary reactions have one or more than one intermediates.
  • Therefore elementary reactions are simple while non-elementary reactions are complex in nature.
  • In elementary reactions, reaction's order equals to the stoichiometric coefficients whereas in non-elementary reactions, reactions order may or may not be equal to the stoichiometric coefficients.
(4)Difference between catalytic and non-catalytic reactions
A reaction in which a catalyst is used to increase the rate of chemical reaction is called catalytic reaction whereas a chemical reaction in which a catalyst doesn't involve in the progress of reaction is called non-catalytic reactions.


Hope you have found this article helpful!!
Do you have suggestions? Please write in comment box!!!
Feel free to comment if you have any queries!!

Comments

Post a Comment

Most Viewed Posts

Zeroth Law Of Thermodynamic: The Thermal Equilibrium Law

Image
In thermodynamics, we will see two types of walls. One is the Diathermic wall and the other is the adiabatic wall. Let us now go through them one by one.  • So the first is the Diathermic wall- " A Diathermic wall is a wall that allows the easy exchange of heat between two bodies (or between two systems or between system and surrounding) but does not allow the exchange of mass between them ". This means that it is a good conductor of heat. It is sometimes called as metallic wall because it is made of metal. • While the other is the adiabatic wall- " An Adiabatic wall is that wall which neither allows exchange of heat nor mass between two systems (or between system and surrounding) ". Since there is no exchange of heat and mass between the system and its surroundings, the system remains insulated from its surroundings. ➛ That's why whenever we separate the two systems by an adiabatic wall, then there is no concept of equilibrium between them. But whenever we sep...
Read more

Characteristics Of Entropy

Image
Entropy is an intrinsic property of a substance and is not affected by the external position of a system or its motion relative to other systems. It is a measure of the randomness of the system. Thus, the higher the randomness of the system, the higher the entropy of the system and the lower the randomness of the system, the lower the entropy of that system. Entropy   " Entropy is defined as a measure of the system's thermal energy that is incapable of doing work ". It is a state function.  For Example Heat is a form of energy that is incapable of doing work. Therefore, the more heat added to the system (or tranfer from the system), the higher (or the lower) will be its entropy.  The formula for change in entropy is given by the equation;                      ➩ ∆S = ∆Q/T For a reversible process, the change in entropy is given as; The Total Change In Entropy Entropy change is zero at equilibrium condition or whenev...
Read more

Reversed Carnot Cycle

Image
We have already discussed the concept of “ Carnot Cycle ”   & “ Its Efficiency ” and we have also seen the concept of “ Carnot Theorem And Its Explanation ” in our previous post. As we have already discussed that the Carnot Cycle is a reversible cycle and every process in the Carnot cycle is a reversible process. Therefore, every process of the Carnot cycle can be reversed. And the cycle can be operated in the opposite direction as well. In this article, we're interested in learning more about the reversed Carnot cycle, also known as the reversed Carnot heat engine cycle. Reversed Carnot Heat Engine It is important to note that if a reversible process is reversed, all related energy types—such as heat energy or work energy—will have the same magnitude but the direction of their interaction with matter will be changed. Let us first look at the Reverse Carnot Heat Engine  cycle here; The reversed Carnot heat engine cycle is depicted in the following figure. According to the...
Read more