Tiêu đề DPP - 2 Solutions.pdf ✅

Class : XIIth Subject : CHEMISTRY Date : DPP No. : 2 1 (a) The ratio of rate constant when temperature is raised 10°C, is called temperature coefficient. For most of the reaction, it has a value of 2. Hence, for the given reaction, Rate constant at 290 K=3.2 × 10―3 ∴ Rate constant at 300 K=2 × 3.2 × 10―3 = 6.4 × 10―3 2 (a) dc dt represent the change in concentration of reactant with time. As, in a reaction, concentration of reactant always decrease with time hence, rate of reaction is represented as ―dc dt . 3 (c) k = 2.303 t log A0 At = 2.303 2 × 104 log 800 50 = 1.386 × 104 s ―1 4 (a) For, N2 +3H2 = 2NH3 Rate of reaction = ― d[N2 ] dt = ― 1 3 d[H2 ] dt = 1 2 d[NH3] dt Where, ― d[N2] dt is rate consumption of N2( ― ve sign) ― d[H2] dt is rate of consumption of H2( ― ve sign) +d[NH3] dt is rate of formation of NH3(+ve sign) Individual rates become equal when each of these is divided by their respective stoichiometric coefficient. 5 (c) Given, R1 = k[A] 2 [B] According to equation R2 = k[3A] 2 [B] = k × 9[A] 2 2[B] Topic :- Chemical Kinetics Solutions
= 18 × k[A] 2 [B] = 18R1 7 (c) For the reaction, A+B →C Rate = k[A] x 0.[B] y 0 Rate2 Rate3 = k(0.024) x (0.070) y k(0.024) x (0.035) y = 0.80 0.10 (2) y = 8 y = 3 Rate3 Rate1 = k(0.024) x (0.035) y k(0.012) x (0.035) y = 0.10 0.10 (2) x = 1 x = 0 Rate = k[B] 3 , where, k=rate constant 8 (c) For second order reaction, dx dt (rate) ∝ [A] 2 ∵ Rate Of reaction increases four times when concentration of reaction is increased two times. ∴ It is second order reaction. 9 (b) N2 + 3H2⇌2NH3 d[H2 ] dt = ―0.3 × 10―4ms ―1 rate = ― 1 3 d[H2 ] dt = + 1 2 d[NH3 ] dt = d[NH3 ] dt = ― 2 3 d[H2 ] dt = ― 2 3 × ( ― 0.3 × 10―4 ) = 0.2 × 10―4 10 (d) According to collision theory, 1. The reaction rate depends on collision frequency and effective collisions. For a molecule to have effective collision it should fulfill two conditions; proper orientation and sufficient energy. 2. The collision rate i.e., the number of collisions taking place in unit volume is also termed as collision frequency (Z) and is given by z = πn 2σ 2uav 2
3. Greater the temperature, greater will be the collision rate. 11 (d) N2(g) +3H2(g)⇌2NH3(g) +22 kcal. ∵ The activation energy for the forward reaction = 50 kcal ∴ The activation energy for the backward reaction=50+22=72 kcal. 12 (d) Only those collisions are effective collisions which are energetic enough and cross over the threshold energy level. 13 (b) k = 0.693 t1/2 = 0.693 480 s ―1 k = 1.44 × 10―3 s ―1 14 (b) It is a characteristic of zero order reaction. 15 (a) Follow review of order of reaction. 16 (a) Average life is defined as, “reciprocal of decay constant.” If decay constant for a reaction is λ then, Average life=1 λ 17 (d) [variation in the concentration Vs time plot for a zero order reaction] 18 (a) Energy of activation does not depend on the stoichiometry of change. It is characteristic value for a chemical reaction. 19 (d) Use ;r = K[A]m[B] n 20 (a) Slow reaction rate indicates higher free energy of activation [R0 ] k= - slope Conc. of R Time
ANSWER-KEY Q. 1 2 3 4 5 6 7 8 9 10 A. A A C A C B C C B D Q. 11 12 13 14 15 16 17 18 19 20 A. D D B B A A D A D A