chemical-kinetics.pdf

u Formulae For CHEMICAL KINETICS By Mir Mohammed Abbas II PCMB 'A' FORMULAS- CHEMICAL KINETICS Important Terms, Definitions & Formulae...

u Formulae For CHEMICAL KINETICS By Mir Mohammed Abbas II PCMB 'A' FORMULAS- CHEMICAL KINETICS Important Terms, Definitions & Formulae XII Chemistry CHAPTER 4 - CHEMICAL KINETICS dx 1. Instantaneous rate = , where dx is small change in conc. and dt dt is the smallest interval of time. ∆x 2. Average rate = , where ∆x is change in concentration and ∆t is ∆t large interval of time. 3. A+B→C+D −d[A] Rate of disappearance of A = , where d[A] is small change in dt conc. of ‘A’ and dt is small interval of time −d[B] Rate of disappearance of B = , dt +d[C] Rate of appearance of C = dt +d[D] Rate of appearance of D = dt −d[A] −d[B] d[C] d[D] Rate = = = = dt dt dt dt Unit of rate of reaction = mol L-1s-1 4. Order of reaction: If rate law expression for a reaction is Rate = k [A]x [B]y Order of reaction = x + y Remember: Order cannot be determined with a given balanced chemical equation. It can be experimentally determined.  FORMULAS- CHEMICAL KINETICS 5. Integrated rate law for zero order reaction: R→P dx = k[R]0 dt Unit of ‘k’ is mol L-1s-1 [R o ] - [R] k = t If we plot a graph between concentration of R vs time, the graph is a straight line with slope equal to -k and intercept is equal to [Ro] 6. Half- life reaction for a for zero order reaction: [R 0 ] t½ = 2k 7. Rate law for 1st order reaction: R→P 2.303 [R ] k = log o t [R] where ‘k’ is rate constant, [Ro] is initial molar conc., [R] is final molar conc. after time ‘t’ 8. Half- Life for a first order reaction is: 0.693 t½ = k 9. Formula to calculate rate constant for first order gas phase reaction of the type A(g) → B(g) + C(g) 2.303 pi k= log t (2pi -pt ) Where: pi is initial pressure of A pt is total pressure of gaseous mixture containing A , B, C Remember: p t = pA + pB + pC 10. Arrhenius equation: k = A e-Ea/RT  k2 Ea  T2 − T1  11. log =   k1 2.303 R  T1 T2  −Ea 12. Rate = P ZAB.e RT Where: ZAB represents the collision frequency of reactants, A and B P is called the probability or steric factor.