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Chemical kinetics

Chemical kinetics : a branch of chemistry which deal about the rate of reaction. Rate of reaction: The change in concentration of reactant or product in a given interval of time is called rate of reaction. Rate of reaction = change in conc. of reactant

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Chemical kinetics

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  1. Chemical kinetics: a branch of chemistry which deal about the rate of reaction. • Rate of reaction: The change in concentration of reactant or product in a given interval of time is called rate of reaction. • Rate of reaction=change in conc. of reactant • Time interval Chemical kinetics

  2. A+B C+D Rate=-[d A]\dt = -[dB]\dt =[dC]\dt =[dD]/dt

  3. Factor affecting the rate of reaction . • Concentration of reactants: The rate of reaction is directly proportional to the conc. Of reactant. The effect of conc. of reactant is also given by law of mass action. 2 Nature of reactants: The nature of reactant is determined by its inner composition thus for ionic reaction. The ratio is very high while if the reactant not strong chemical bond the rate of reaction less

  4. Temperature: the rate of chemical reaction increase with increase in temperature generally rate of reaction increase twich as the temperature is increased by 10k such effect of temperature is called temperature coefficient. • Catalyst: A catalysts is a substance which do not participate in a reaction but alter the rate of reaction. • Law of Mass action: according to this law the rate of chemical reaction is directly preoperational to the product of the molar conc. Of the reactants with each term raised to the power equal to its coefficient • aA +bB Product • rate [A

  5. Characteristic of rate constant • For a particular reaction the rate constant is independent of conc. • The rate constant only depends upon temperature. • The value of K is different for different reaction. • Greater the value of K greater will be the rate of reaction • A + B C + D K1 C + D A + b K2 K2=1\K1

  6. If two chemical reaction are added than the rate constant are multiply • If two reaction is subtracted then the rate constant are divided. • If a chemical reaction is multiplied by n than rate constant than K2 =K1n • Molecularity: Number of molecules which participate in the elementary state in any chemical reaction is called molecularity. On the basis of moleculatity reaction are three type.

  7. Unimolecular reaction: • O3 O2+[O] • N2O5 N2O4 +O2\2 • Bimolecular reaction: • 1HI H2+ I2 • NO+ O3 No2+ O2 • Trimolecular reaction: • 2NO +O 2NO2 • 2SS2+O2 2So3 • In case of complex reactions The molecularity of slowest step is considered 1

  8. Order of reaction: The sum of all exponent of concentration of reaction which appear in differential rate equation is know as order of reaction it is denoted by n. • Order of reaction is an experimental value its fractional value are possible .it zero value is also possible it provided information about machanism of reaction . • aA+bB+cC=product

  9. Zero order reaction : in this reactions the rate of reaction does not depend upon conc. Of reaction . 2NH3 N2 +3H2 rate = K[NH3]0 • First order reaction: • All radioactive changes • Dissociation of ammonium nitrate • NH4NO3 N2O +2H2O rate = k[NH4NO3]1 • Decomposition of hydrogen peroxide • H2O2 H2O +O

  10. Rate = k H2O2] • Second order reaction: • Desociation of hydrogen iodide 2HI H2 + I2 Rate =k[HI]2 • Desociation of nitrogen peroxide 2NO2 2NO+ O2 RATE = K[NO2] • Third order reaction • Reaction between nitric oxide and oxygen 2NO +O2 N2O4 RATE =K[NO]2[O2]1

  11. Soudo unimolecular reaction or Soudo first order reaction Such reaction in which the molar concentration of a reactant remain partially unchanged and the small change in conc. Does not effect the rate of reaction are called soudo unimolecular reactions. Thus , a reaction which is first order reaction but it look like second order reaction known as soudo unimolecular reaction. Example:- hydrolysis of ester CH3COOC2H5 +H2O CH3COOH +C2H5OH Rate = K[CH3COOC2H5] =

  12. Hydrolysis of Sucrose:- C12H22O11 +H2O C6H12O6 +C6H12O6 Rate = k[C12H22O11] • Units of rate constant for different order of reaction rate = k[concentration] Unit of k= moles/liter.sec • For first order reaction rate =k[conc.]1 Unit of k =1\sec • For second order reaction rate = k[conc.]2 Unit of k = liter\moles.second

  13. For third order reaction Rate = k[conc.]3 Unit of k =liter2\moles2.sec * Rate constant for the first order reaction A product rate =k[A]1 • consider initial conc. Of reaction be ‘a’ after ‘t’ time ‘x’ amount of product is formed • Thus the conc. Of reactant after ‘t’ time equal to (a-x) .thus k = 1\t*log a\a-x

  14. k =2.303 log10 a t a-x • Half life period:- The time in which half of the reaction is called half life period. It is denoted by ‘t1\2‘ For the half order reaction k =2.303 log10 a t a-x if t =t1\2 a-x = a\2

  15. k =2.303 log10 a log102=0.3010 k =2.303*0.3010\t1\2 k =0.693\t1\2 t1\2 =0.693\k • Expression for rate constant of first order reaction A product Rate =-[dA]\dt rate = k[a] -[dA]\dt = k.[a] t1\2 a\2

  16. -[dA]\dt = k.dt on integrating the above equation -log A =kt +c [integration constant] At t=0 , A = A0 -loge A0 = c -loge A =kt -loge A0 loge A0 -loge A =kt loge A0\A =kt k =1\t logeA0\A k = 2.303\t .log10 A0\A

  17. Effect of temperature on rate constant OR • Arrhenius equation Arrhenius gave a relation between rate constant and temperature which is known as Arrhenius equation. According to this equation k = A.e–Eq/RT where , k = rate constant A = frequency factor EA = Activation energy R = Universal gas constant

  18. T =Temperature in Kelvin on taking log both the side loge K = loge A.e –Eq/RT loge K = loge A + loge e –Ea/RT loge K = loge A -Ea/RT loge e loge e = 1 loge K =loge A - Ea/RT 2.303 log10 K = 2.303 log10 A - Ea/RT log1 K = log10 A - Ea/2.303 RT for a reaction , the rate constant at t1 temperature, while at t2 temperature it will be K2 (T2 > T1) than,

  19. log10 K1 = log10 A -Ea/2.303 RT1 ------------(1) log10 K2 = log10 A - Ea/2.303RT2 -----------(2) on subtracting (1) from (2) log10 K1 - log10 K2 =Ea/2.303 RT2 -Ea/2.303 RT1 log10 K1/K2 = Ea/2.303R [1/T2 - 1/T1] *Theracehold Energy : The minimum amount of energy which is required by molecules of reactant for the fruitful collision is called teracehold energy. *Energy barrio : The amount of energy at which molecules of reactant collides and converted into product is called energy barrier

  20. Activation energy : The amount of energy which is required by the molecules of reactant to cross the energy Barrier is called activation energy. Activation energy = Theracehold energy - Energy of reactant

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