What is half life of reaction and how it can calculated? , Chemistry

Assignment Help:

 

Half life of reaction refers to as the time during which the concentration of the reactants is reduced to half of the initial concentration or it is the time essential for the completion of half of the reaction. It is denoted by 11/2.

Half life of zero order reaction: as already discussed, the integrated equation for zero order reaction is;
                                               
[R] = [R]0 – kt
                                    
Now at t1/2, [R] = ([R]0)/2
                                                             
  ([R]0)/2 = [R]0 – kt
                          
Or, kt1/2 = [R]0 – ([R]0)/2 = ([R]0)/2
                                          
Or, t1/2 = ([R]0)/2k


From the above expression it is clear that the half life of a zero order reaction is directly proportional to initial concentration.
                                                   
i.e. t1/2 [A]0
                                  
At t3/4, the concentration [R] = ¼ [R]0
                                    
t3/4 = 1/k R0-  1/4[R]0) = 3/4 [R0)/k 
                                         
Hence, t3/4 = 3/2 t1/2 = 1.5t1/2

Half life of first order reaction: for first order reaction, we know that
                                    
k = 2.303/t log ([A]_0)/([A]) or t = (2.303)/k log ([A]_0)/([A])
                                        
When t = t1/2 then [A] = ½ [A]0,
                                     
Therefore, t1/2 = (2.303)/k ½ ([A]_0)/([A]) = (2.303)/k  log 2
                                        
t1/2 = 0.693/k           [? log 2 = 0.3010]

It is quite clear from the above expression that the half life or half change time for first order reaction does not depend upon initial concentration of the reactants. Likewise, the time required to decrease the concentration of the reactant to any fraction of the initial concentration for the first order reaction is also independent of the initial concentration.


Related Discussions:- What is half life of reaction and how it can calculated?

Freons, Which is a better coolant, Freon 11 or Freon 12? why?

Which is a better coolant, Freon 11 or Freon 12? why?

Gibbs free energy and spontaneity, Q. Describe Gibbs Free Energy and Sponta...

Q. Describe Gibbs Free Energy and Spontaneity? Ans. This is the end of the quest to find spontaneity.  Free Energy, or Gibbs Free Energy is a quantity which balances the r

Surface tension, surface tension assingnment with diagram

surface tension assingnment with diagram

Assignment, Redox systems in bioinorganic chemistry

Redox systems in bioinorganic chemistry

Biosorption of dyes, biosorption of methylene blue dye using acid treated m...

biosorption of methylene blue dye using acid treated mango leaf powder

General and physical characteristic of proteins, General and physical chara...

General and physical characteristic of proteins (a) Most of them apart from chromoproteins are colourless, tasteless, and odourless. Several are amorphous but few are crystalli

Element have electronegativity, Two element have electronegativity of 1.2 a...

Two element have electronegativity of 1.2 and 3.0. Bond formed between them would be: (1) Ionic (2) Polar covalent ( 3) Co-ordinate (4) Metallic A ns: Ionic

Organic chemistry, how will you prepare iodoform in labarotary?

how will you prepare iodoform in labarotary?

Transfer of electrons from lower to higher energy levels, The electrons  wo...

The electrons  would go to lower energy levels first and then to higher energy levels according to which of the following: (1) Aufbau principle (2) Pauli's exclusion princip

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd