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# Intro to reaction enggineering

it contains basics of chemical reaction engineering

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### Intro to reaction enggineering

1. 1. Introduction to Reaction Engineering
2. 2. CHEMICAL KINETICS  The branch of physical chemistry which deals with the rate of chemical reactions and the mechanism through which they occur is called chemical kinematics.
3. 3. CLASSIFICATION OF CHEMICAL REACTION  (1) Homogeneous and Heterogeneous reaction  (2) Catalytic and Non-Catalytic reaction  (3) Based on Molecularity of Reaction  (4) Exothermic and Endothermic reaction  (5) Based on order of reaction  (6) Reversible and Irreversible reaction
4. 4. Rate of chemical reaction  Rate of reaction can be define based on unit volume of reacting fluid in case of homogeneous system based on unit mass of solid in case of fluid-solid system and so on.  select one reaction component for consideration and define the rate in terms of this component i.  If the rate of change in number of moles of this component due to reaction is dNildt, then the rate of reaction in its various forms can be determioned
5. 5. Order of a reaction  The sum of the powers of concentration terms in rate equation is known as order of reaction. (or)  Order of given with respect to all participating reactants in which case it is called order of reaction. Consider a reaction mA + nB product Rate eq (R)=k[A]m[B]n Order = m + n
6. 6. Zero Order Reaction  When the reaction rate is independent of concentration of the reacting substance, it depends on the zero power of the reactant and therefore is zero order reaction.  The unit of K is concentration time-1 with typical units of mole L-1 s-1.  Half-life is given by equation; t1/2 = C0/2k
7. 7.  The unit of K is concentration time-1 with typical units of mole L-1 s-1.  Half-life is given by equation; t1/2 = C0/2k
8. 8. First order Reaction  First order reaction consists of one reactant. A product R = k[A]1  Rate constant for first order reaction: k = 2.303 * log(a/a-x) t where, a=initial conc. of A in mol/lit a-x=change in initial conc. of A in mol/lit in time interval ’t’
9. 9. Half Life Time (t1/2)  Time taken for initial conc. of reactant to become half of its volume k= 0.693/t1/2 t1/2=0.693/k  Units of rate constant for first order reaction: sec-1
10. 10. Examples of first order reaction  Thermal decomposition of N2O5 N2O5 N2O3+O2  Hydrolysis of hydrogen peroxide H2O2 H2O +1/2O2  Decomposition of Calcium carbide CaCO3 CaO + CO2
11. 11. Second Order Of Reaction  Second order reaction consists of two reactants. 2A Products A+B Products Rate = k[A]2 ; n=2 Rate = k[A][B] ; n=1+1=2
12. 12. Half Life Time  Half life time for second order reaction: t1/2 = 1/a n-1 =1/a as n=2  Units: k = mol -1 lit sec -1 (or) = conc-1. sec -1
13. 13. Examples Of Second Order Reaction  Thermal decomposition of Nitrous oxide 2N2O 2N2 +O2  Decomposition of NO2 2NO 2NO +O 2  Decomposition of Hydrogen Iodide 2HI H 2 + I2
14. 14. Third Order Reaction  Third order reaction includes three reactants 3A Products r = k [A] 3 A+B+C Products r = k [A] [B] [C] 2A+B Products r = k [A]2 [B]
15. 15. Molecularity of the reaction  The number of ions or atoms or molecules involve in the rate determining step or rate limiting step is called molecularity .  The molecularity will be only whole number and never be zero or fraction.  Molecularity can be determined by reaction mechanism but it cannot be determined experimentally.
16. 16.  In no chemical reaction reactants are directly converted into products in single step, initial reactants are converted to final products occurred by different internal steps . These steps are called elementary step reactions .  The sequential representation of elementary reaction step in overall chemical reaction is called reaction mechanism.
17. 17. Example: A B Reaction Mechanism: A 2x 2x 2y 2y B (slow)  Among all three steps there is a elementary step with least reaction . This step is called rate determining step or rate-limiting step.
18. 18.  Molecularity cannot exceed ‘3’ . If one molecule is involved in elementary reaction then the reaction is uni- molecular in nature. CH2 CH2 2C2H4 CH2 CH2  In bimolecular reaction the two reactant molecules(same or different) participate to cause a chemical change. 2HI H2 + I2
19. 19.  In tri-molecular there will be collision of three molecules. 2NO + O2 2NO2
20. 20. Molecularity  It is defined as number of molecules or atoms or ions participating in rate determining step.  It is a theoretical quantity, which can be determined through reaction mechanism.  It is always whole number or integer. It can never be fraction or zero. Order of reaction  Order is defined as sum of powers of concentration terms in a rate equation.  Order of reaction can be determined experimentally.  Order of reaction is zero , fraction , integer & whole number.