Chemical Kinetics Name: Batch: Date: Rate f reactin. 4NH 3 (g) + 5O (g) à 4NO (g) + 6 H O (g) If the rate f frmatin f NO is 3.6 0 3 ml L s, calculate (i) the rate f disappearance f NH 3 (ii) rate f frmatin f H O. 3 3 [Ans.(i) 3.6 0 mll s,(ii) 5.4 0 mll s ]. Hw many times must the cncentratin f substance B in the system(fr elementary reactin) A (g) + B (g) à A (g) be increased fr the rate f frward reactin t remain unchanged when the cncentratin f substance A is lwered t ¼ th f its initial cncentratin f A =, B =. [Ans. 6 times] 3. Hw many times will the rate f the reactin A + B à A B(fr elementary reactin) change if the cncentratin f A is dubled and that f substance B is halved? Assuming elementary reactin. [Ans. Tw fld] 4. Fr the fllwing reactin A + B + C à A B + C the rate law has been determined t be Rate = k[a][b] with k =.0 0 6 ml L s Fr this reactin determine the initial rate f the reactin with [A] = 0. ml L [B] = 0. ml L [C] = 0.8 ml L. Determine the rate after 0.04 ml L f A has reacted. 9 9 [Ans.() 8 0 mll s,() 3.8 0 mll s ] 5. Shw by using rate law, hw much rate f the reactin NO + O à NO (elementary reactin) will change if the vlume f the reactin vessel is reduced t ne third f its initial value? [Ans. 7 times] 6. The decmpsitin f N O 5 in carbn tetrachlride slutin was studied N O 5 (slutin) à NO (slutin) + ½ O (g) The reactin has been fund t be first rder and the rate cnstant is fund t be 6. 0 4 s. Calculate the rate f reactin when (a) [N O 5 ] =.5 ml L and (b) [N O 5 ] = 0.5 ml L. What cncentratin f N O 5 wuld give a rate f.4 0 3 ml L s? [Ans. (a) 7.75 0 4 ml L s (b).55 0 4 ml L s : cnc = 3.8 ml L ] Order f the reactin 7. (a) Define the term Rate cnstant r specific reactin rate. (b) What is meant by rate cntrlling step in a reactin? (c) What is difference between mlecularity f reactin and rder f reactin? 8. Fr an equilibrium reactin invlving gases, the frward reactin is st rder while the reverse reactin is nd rder. The units f K fr the frward equilibrium is P (A) atm (B) atm (C) atm - (D) atm - Ans: [A] 9. Prve that the half life perid fr a reactin f nth rder in a reactin A à Prduct is inversely prprtinal t (n )th pwer f initial cncentratin. 0. Fr a gaseus reactin A + B à AB, the fllwing rate data were btained at 300K Rate f disappearance f B Cncentratin (ml lit min ) [A] [B] (i).8 0 3 0.05 0.5 (ii).08 0 0.09 0.5 (iii) 5.4 0 3 0.05 0.45 Calculate the rate cnstant fr the reactin and rate f frmatin f AB when [A] is 0.0 and [B ] is 0.04 ml lit at 300 K. [Ans. 0.8 litre ml min and.8 0 3 ml lit min ]
. The fllwing rate data were btained at 300 K fr the reactin A + B à C + D Calculate the f frmatin f [A] = 0.8 and [B] = 0.5 ml L Experiment [A] ml L [B] ml Rate f frmatin f D ml L N. L min 0. 0. 7.5 0 3 0.3 0. 9.0 0 3 0.3.04 3.6 0 4 0.4 0. 3.0 0 rate D when ml L [Ans..5 ml L min ]. Fr the frmatin f phsgene gas frm CO and chlrine: CO + Cl COCI, the fllwing mechanism is suggested CI É CI (fast) CO + CI É COCI (fast) COCI + Cl COCI + CI (slw) Suggest the rate law equatin fr it. [Ans: r = K[[CO][Cl ] 3/ ] 3. Fr the thermal decmpsitin f zne t xygen, the fllwing mechanism has been suggested K Step : O áààà àààüà O + O; Step : O 3 + O 3 K k O Shw that rate law viz., r = -k [O 3] / [O ]. 4. Fr a reversible reactin NO É NO, the rate f disappearance f 4 NO is equal t k (A) [ ] k NO (B) k [ NO ] k [ N O ] 4 (C) k [ ] NO k [ NO4] (D) ( k k )[ NO ] First rder reactin and t / 5. A first rder reactin takes 63.5 minutes fr 50% cmpletin. Hw much time will be needed fr 80% cmpletin. [Ans. 60.9 mins.] 6. Find the f time expressed in units f t / at which A/A 0 = 0.5 fr the first rder reactin Ans: [t=3t / ] 7. The half life f a first rder reactin is.4 min. In what time the reactin will cmplete 87.5%? [Ans : 67. min] 3 8. If fr a reactin A prducts, the cncentratins f A are C, ac, ac, ac.after time interval 0, t, t, 3t where a is cnstant and 0 < a <, shw that reactin first rder kinetics. 9. The specific reactin rate fr a first rder reactin is 0 ml litre sec. What will be the reactin rate after tw minutes assuming initial cncentratin mlar. [Ans.3 0 3 ] 0. The specific rate cnstant f the decmpsitin f N O 5 is 0.008 min -. The vlume f O cllected after 0 minutes is 6 ml. Find the vlume that wuld be cllected at the end f reactin NO frmed is disslved in CCl 4.. At 00 C, a gaseus reactin A B C + is bserved t be a st rder. On starting with A, at the end f 4 minute, the ttal pressure was fund t be 64 mm f Hg. After a lng time the ttal pressure f the system was 450 mm f Hg. Calculate (a) initial pressure f A, (b) rate cnstant f reactin, (c) half life perid f reactin.
. Fr the reactin A à B + C the fllwing data were btained t(sec) 0 900 800 [A] 50.8 9.7 7.6 Prve that reactin is f first rder. CHAPTER PRACTICE PROBLEMS CHEMISTRY [Ans:- (a) 50 mm, (b) 3.45 0 - min -, (c) 0.9 min] 3. Frm the fllwing data fr the decmpsitin f N O 5 in carbn tetrachlride slutin at 3 K, shw that the reactin is f the first rder and calculate the rate cnstant. Time (in minutes) : 0 5 0 5 Vl. f O evlved : 6.30 8.95.40 3.50 34.75 4. In the dehydratin f xalic acid by cnc. H SO 4 (COOH) à CO + CO + H O cm 3 f the slutin were withdrawn at different times and titrated against 0. N KMnO 4 slutin. The fllwing data were btained: Time (min) : 0 300 450 600 Vl. f KMnO 4 used (cm 3 ) :.0 7.0 5.0 3.4 shw that the reactin is f the first rder 5..0 ml f ethyl acetate was added t 5 ml f N/ HCl. ml f the mixture were withdrawn frm time t time during the prgress f the hydrlysis f ester and titrated against standard NaOH slutin. The amunt f NaOH required fr titratin at varius intervals is given belw: Time (in minutes): 0 0 75 9 83 Vl. f O evlved: 0.4.73 5.0 7.60 30. 43.95 The value at time was btained by cmpeting the hydrlysis n biling. shw that the reactin is f the first rder and calculate the rate cnstant. Pressure related prblemes 6. The gas phase decmpsitin f dimethyl ether fllws first rder kinetics, CH OCH g CH + H + CO g ( ) ( ) ( ) ( ) 3 3 4 g g The reactin is carried ut in a cnstant vlume cntainer at 500 C and has a half life at 4.5 minute. Initially nly dimethylether is present at a pressure f 0.40 atmsphere. What is the ttal pressure f the system after minute? Assume ideal gas behavir. [Ans:- Ttal pressure = 0.75 atm] 7. The gas phase decmpsitin (in clsed cntainer), A (g) à 4B (g) + C (g) fllws the first rder rate law. At a given temperature specific reactin rate is 7.5 0 3 S. The initial pressure f A is 0. atm. Calculate the time f decmpsitin f A s that the ttal pressure becmes 0.5 atm. [Ans:- 38sec] 8. Fr the first rder reactin, A (g) (B)g + C(g), the ttal pressure, after time t frm start f reactin with A is P and after infinite time, it is P. Then the rate cnstant f the reactin is (A) P In t P (B) P In t 3 P P ( ) P (C) In t 3P P P (D) In t P 3P Arrhenius equatin 9. The rate cnstant f a reactin is. 0 3 sec at 30 0 C and. 0 3 sec at 40 0 C. Calculate the energy f activatin f the reactin. [Ans. E a = 44.3 kj ml ] 30. The rate f a particular reactin dubles when temperature changes frm 7 0 C t 37 0 C. Calculate the energy f activatin f such a reactin. [Ans. E a = 53.6 kj ml ] 3. The activatin energy f a reactin is 94.4 kj ml and the value f rate cnstant at 33 K is.8 0 5 sec. Calculate the frequency factr,a. [Ans. A = 9.94 0 0 cllisins/sec.]
3. A hydrgenatin reactin is carried ut at 500 K. If the same reactin is carried ut in the presence f catalyst at the same rate, the temperature required is 400 K. Calculate the activatin energy f the reactin if the catalyst lwers the activatin energy by 0 KJ/ml. [Ans: 00KJ/ml] 33. If activatin energy f a reactin is 80.9 k J per ml. Calculate the fractin f mlecules at 400 0 C which have enugh energy t frm prducts. [Ans: ] k k 34. Fr a reactin, if the effective rate cnstant k is given by k = k 3 k 4 fr the rate cnstants fr the different steps f the reactin. /. Calculate the k,k,k and k 3 4 stand A A [Ans: Ea = Ea E a + E 3 a E 3 a ;A = ] 4 A3 A4 35. The gaseus phase reactin f pinene beying rder kinetics has specific rate cnstant as. 0-5 min - and 3.07 0-5 min - at 457.6 K and 50. K respectively. Calculate (a) energy f activatin and (b) specific reactin rate at 480 K. [Ans:- (a).96 Kcal ml -, (b).56 0-5 min - ] 36. Fr the reactin, SnO (s) + H (g) H O (g) + Sn (s). At 500 K, where the steam hydrgen mixture has 5% H by vlume and at 700 K it was 0% H by vlume. Calculate the activatin energy f the backward reactin, if the activatin energy fr the frward reactin is 39.9 kj ml 37. Tw secnd rder reactins given belw having identical frequency factrs:- (I) A Pr duct (II) B Pr duct If activatin energy f first reactin is 0.46 KJ/ml mre than that f B. At 00 C, the reactin (I) is 30% cmpleted after 60 minutes when initial cncentratin f A is 0. ml/l Hw lng will it take fr reactin (II) t reach 70% cmpletin at the same temperature if initial cncentratin f B is 0.05 ml/lit [Ans:-. min] Multi cncepts 38. True / False : (I) half life in independent f initial cncentratin nly fr zer rder reactin (II) Changing the pressure, changes the rate cnstant (III) Elementary reactins with mlecularity greater than 3, generally d nt ccur (IV) If the partial rders differ frm the cefficients in the balanced reactin, the reactin must be cmplex (V) Fr a reactin with E a > 0, the greater the activatin energy, the mre rapidly the rate cnstant increases with temperature. (VI) The pressure f a hmgeneus catalyst cannt change the equilibrium cmpsitin f a system [Ans:- F,F,T,T,F.F] Cmplex Reactins 39. A reactin fllws parallel path f st rder reactins giving B and C as 5A λ B C λ If initial cncentratin f A is 0.5M. Calculate the cncentratin f C after 5 hurs f reactin. 5 6 λ =.5 0 sec and λ = 5 0 sec [Ans:- 7.56 0-3 M] 40. 84 P 8 (t / = 3.05 mins) decays t 8 Pb 4 (t / =.68 min) by α - emissin, while Pb 4 is a β -emitter, In an experiment starting with g atm f pure P 8 hw much time wuld be required fr the number f nuclei f 8Pb 4 t reach maximum. k = In3 min- k = In3 min - A B A C
4. In the parallel reactins: and, the time when the cncentratins f A, B and C becmes equal is (A) 0.5 s (B) 30 s (C) 45 s (D) 60 s 4. In the given first rder sequential reactins: A k B k C k 3 D, what is the rati f number f atms f A t the number f atms f B after lng time interval starting with pure A? In In k = and k = 00 30 (A) 0.67 (B) 0 (C) 0 (D) 40 [Ans: D]