Use Coupon: CART20 and get 20% off on all online Study Material

Total Price: R

There are no items in this cart.
Continue Shopping
Get instant 20% OFF on Online Material.
coupon code: MOB20 | View Course list

Get extra R 520 off


can we have any reaction having activation energy zero

7 years ago


Answers : (1)


We can have  reaction with zero activation energy,at least theoretically it can even be negative......!!!!

It might help to distinguish clearly between:
a) net energy gain of the reaction, which, yes, can be either positive or negative,
b) activation energy, which is a little road-bump, or wall, or barrier, in between the
before-reaction situation and the after-reaction situation.

     So a negative reaction energy would be like a deep trench between a floor and a
small step.  (The step could be up or down.)  A trench might stop walking people,
but it does not usually stop atoms.  They would more likely roll down into the
trench,gain momentum, and roll right back out with just as much energy as they had before.  
i.e. no barrier, same effect as zero activation energy.
    A barrier which sticks up, like a wall sticks out of the ground, would stop
randomly rolling balls if they were not rolling fast.  Even if the other side of
the wall is lower.
Likewise, a positive activation energy stops atoms from reacting if they are cold. 
Even if reacting would gain energy.

You must ask yourself, why does it take a match to start a fire?
Why does air not just burn all paper on contact?
That is what activation energy is about.

But here is anothe catch.....!!!!!!

The expression for the activation energy, Ea,: d[ln (k)]/dT = Ea/RT^2 is
an argument by analogy to the analogous thermodynamic expression for the
enthalpy of reaction and the temperature dependence of  the equilibrium
constant. It does not apply to reactions that decrease in rate as the
temperature increases. It does not apply to a lot of chemical reactions.
Reaction rates can increase, decrease, remain constant, increase then
decrease, decrease then increase, or even be essentially discontinuous with
an increase in temperature. The concept of an activation energy should not
be taken too literally. Reaction kinetics are much more complicated.

In some cases rates of reaction decrease with increasing temperature. When following an approximately exponential relationship so the rate constant can still be fit to an Arrhenius expression, this results in a negative value of Ea. Reactions exhibiting these negative activation energies are typically barrierless reactions, in which the reaction proceeding relies on the capture of the molecules in a potential well. Increasing the temperature leads to a reduced probability of the colliding molecules capturing one another (with more glancing collisions not leading to reaction as the higher momentum carries the colliding particles out of the potential well), expressed as a reaction cross section that decreases with increasing temperature. Such a situation no longer leads itself to direct interpretations as the height of a potential barrier.

Having gone through all of the above arguments i believe that Ea could be either zero or positive but for ideal case of Arrhenious Equation only.For all practicality it is always positive.

I hope above will help you in your query.Any further clarifications if required by you will be most certainly entertained here.

7 years ago

Post Your Answer

Other Related Questions on Physical Chemistry

What is metallic corrosion......................................?
Natural tendency of conversion of a metal into its mineral compound on interaction with environment is known as corrosion.
SAI SARDAR 3 months ago
@ ram Corrosion is a natural process, which converts a refined metal to a more stable form, such as its oxide, hydroxide, or sulfide. It is the gradual destruction of materials,by chemical...
Umakant biswal 3 months ago
I have a many books for physics H C Verma class12,ABC physics class12,ncert physics class12,and rudiments physics mcq and i am also taken a tution of physics then i am confused how i study...
@ manish What u need to understand is that , every book explains the same concept , every author have diffrent approach to explain the same concept . so, by that i can say first of all...
Umakant biswal 3 months ago
look brother dont get scared by seeing all thoose books.just leave all the rubbish biooks except hc verma ad ncert .never leave them.all your friends will be dong that and this books.just...
sunny 3 months ago
What is the radius of Li 2+ ion in 2nd orbit and please give me the formula
@ piyush u haVE to use the below formula r (n ) = n ^ 2*0.529* 10^ -10 / zm z = atomic number = 3 n = 2 (as given 2 nd orbit ) just put the value in the formula and calculate it . r (n ) =...
Umakant biswal one month ago
The formula of finding the radius of atom = 0.529 * n^2/Z So, here the ‘n’ is 2 & ‘Z’ is 3 Then, Radius=0.529 * 4/3 =0.705
Lakshit one month ago
Except F2 all the halogens forms the oxides. Cl has largest number of synthesis of oxides. Examples: Cl2O, ClO2, Cl2O6, Cl2O7 Br2O, BrO3, BrO2C. I2O5 , I2O7. the synthesis reaction would...
Vikas TU 3 days ago
Urea is stronger base than ordinary amide?according to lewis theory
Urea has two nitrogen having two lone pair of electrons. Acetamide had only one nitrogen and only one li=one pair of electrons. Urea is a stronger base because it has lower pKb than...
dolly bhatia 2 days ago
amide are weak base due to the resonance of the amide group . in acetamide , the lone pair nitrogen are not avaliable for bonding , with h ^+ . however in urea , the lone pair of second nh2 ...
Umakant biswal 2 days ago
The reason is: As the lone pair in Urea is freely available and thus not participates in any Resonance. But in any ordinary amide the lone pair is conjugated with the resoace and hence...
Vikas TU 2 days ago
Assuming pure 2s and 2p orbitals of Carbon are used in forming CH4 molecule, which if the following is false? (a) 3 C-H bonds will be at right angles (b) 1 C-H bond will be weaker than other...
CH4 has tetrahederal structure orientation with sp3 hybridization. hece 4 C-H bonds would be at equal angles with each C-H bond. and that would be 109.5 degree and that is practically...
Vikas TU 2 months ago
View all Questions »

  • Complete JEE Main/Advanced Course and Test Series
  • OFFERED PRICE: R 15,000
  • View Details
Get extra R 3,000 off

Get extra R 520 off

More Questions On Physical Chemistry

Ask Experts

Have any Question? Ask Experts

Post Question

Answer ‘n’ Earn
Attractive Gift
To Win!!!
Click Here for details