(Preeti  Aghalayam,  Oct  2011)  

IIT-M 10.5 K LoopPublic ! 2 Collaborators ! 201 viewsCreated on Sep 12 ! By Ram ! Updated Sep 12

Created by My Tracks on Android.Total Distance: 10.90 km (6.8 mi)Total Time: 1:05:37Moving Time: 1:05:25Average Speed: 9.97 km/h (6.2 mi/h)Average Moving Speed: 10.00 km/h (6.2 mi/h)Max Speed: 18.00 km/h (11.2 mi/h)Min Elevation: -95 m (-312 ft)Max Elevation: -67 m (-220 ft)Elevation Gain: 233 m (764 ft)Max Grade: 4 %Min Grade: -1 %Recorded: Mon Sep 12 17:30:03 GMT+05:30 2011Activity type: -

2011-09-12 17:30 (Start)

2011-09-12 17:302011-09-12 17:30 (End)

http://www.chennairunners.com/      Nov  6th  @  6  am    10km  &  half  marathon  race  

!! ! !!!!!!!!!!

Perpendicular  adsorption  

Parallel  adsorption  

Homonuclear  molecule  

Strong  Binding  

Weak  Binding  

A+B  

AB  

AB*  

A*+B*  

DAB  

ΔHads,  molecular  

Potential    Energy  

Distance  from  Surface  

ΔHads,  atomic  

A+B  

AB  

AB*  

A*+B*  

DAB  

ΔHads,  molecular  =  QAB  

Potential    Energy  

Distance  from  Surface  

ΔHads,  atomic  =  QA+QB  

A+B  

AB  

AB*  

A*+B*  

DAB  

ΔHads,  molecular  =  QAB  

Distance  from  Surface  

ΔHads,  atomic  =  QA+QB  

The  intersection  between  the  atom  adsorption  &  the  molecular  adsorption  PE  curves  can  tell  us  about  the  activation  energy  for  dissociative  adsorption  of  AB  

Case  1   Case  2  

UBI-‐QEP  assumptions  allow  the  calculation  of  activation  energy  for  the  simple  dissociation  reaction  :      as      If  the  dissociation  occurs  from  the  adsorbed  phase:      

AB+ 2*! A*+B*Eact =

12DAB !QAB !QA !QB +

QAQBQA +QB

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Thus,  with  reliable  input  values  for  the  atomic  and  molecular  heats  of  chemisorption,  the  activation  energy  for  the  reaction  is  easily  calculated  

AB*+*! A*+B*

Eact =12DAB +QAB !QA !QB +

QAQBQA +QB

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¡  The  assumptions  are  easily  extended  to  a  disproportionation  reaction  of  the  form:    

       (where  DBC>DAB),  to                here,              

A*+BC*! AB*+C *

Eact =12!Hrxn +

QABQCQAB +QC

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!Hrxn = DBC "DAB +QA +QBC "QAB "QCActivation  energies  for  all  classes  of  Langmuir-‐Hinshelwood  surface  reaction  steps  (on  metal  catalysts)  are  evaluable  using  these  two  formulae  

¡  The  activation  energies  for  the  reverse  reactions  are  calculated  as:    

¡  In  any  reaction  mechanism,  maintaining  thermodynamic  consistency  is  very  important  

¡  The  heats  of  adsorptions  of  all  involved  surface  species  are  the  only  independent  reaction  heats  in  a  given  reaction  mechanism  

Eb = Ef !"Hrxn

¡  With  these  formulae,  UBI-‐QEP  allows  us  to  develop  reaction  mechanisms  for  various  systems  catalysed  by  metals  

¡  In  research  articles,  you  will  see  authors  use  experimental  values  where  available,  and  consistent  UBI-‐QEP  values  to  Qill  in  the  gaps.  

¡  Some  of  the  neat  extensions  of  this  work  are  §  Application  to  metal  alloys  §  Dealing  with  coverage  dependent  reaction  energetics  

AB+ 2*! A*+B* Eact =12DAB !QAB !QA !QB +

QAQBQA +QB

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AB*+*! A*+B* Eact =12DAB +QAB !QA !QB +

QAQBQA +QB

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A*+BC*! AB*+C * Eact =12!Hrxn +

QABQCQAB +QC

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Formulae  for  activation  energy  calculations  

Lets  construct  a  reaction  mechanism  for  ammonia  synthesis  (Today,  we  will  write  down  a  few  main  reactions,  and  Qind  reaction  heats)