10. A second-order reaction is found to take 124 seconds for the reactant concen

Question

10. A second-order reaction is found to take 124 seconds for the reactant concentration to drop from 1.6M to 0.15M. How much longer deplete by a concentration of 0.06MP will it take for the reactant to further The concentration ofa reactant in zeroth order drops from 2.5M to 1.75M in 57 seconds. What is the final concentration after 89seconds if the starting concentration is 1.5M 1· 11. A second order reactant has a half-life of 50s. How long will it take for the reaction to be 30% complete? 12. A first ord er reaction has a rate constant of 1.3xl0' s . How long in minutes will it take for the reactant concentration to drop from .8M to .35MP

Explanation / Answer

10. standard rate equation of second order reaction

1/[A] = 1/[A0] + kt

[A] = concentration at time t and [A0] = concentration at t=0 and k =rate constant

1/0.15 = 1/1.6 + k*124

k = 0.0488 M-1 s-1

now, after depletion [A] = 0.15 - 0.06 = 0.09 M

1/0.09 = 1/1.6 + 0.0488 *t

or, t = 215 s

it will take further (215 -124) = 89 s for depletion of 0.06 M

1. for zero order reaction

[A] =[A0] - kt

now, 1.75 M = 2.50 M - k*57 s

or, k = 0.013 M s-1

[A] =1.5 M - 0.013 M s-1 * 57 s = 0.759 M (answer)

11. t1/2 = 50 s

standard rate equation of second order reaction

1/[A] = 1/[A0] + kt

or, 2/ [A0] = 1/[A0] + k*50

or, k = 1/(50*[A0] ) M-1 s-1

now, [A] = 0.3 [A0]

1/  0.3 [A0] = 1/[A0] + 1/(50*[A0] *t

or, t = 116 s (answer)

12. first order reaction

ln[A] =ln[A0] - kt

or, ln(0.8) = ln(0.35) - 1.3*10-8 *t

or, t =6.3*107 s =0.105*107 m

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