Use the References to access important values if needed for this question the fo

Question

Use the References to access important values if needed for this question the following data for the decomposition of nitrosyl bromide at 10 °C NOBr(g)--NO(g) + ½ Br2(g) NOBr], M seconds 0.242 0.121 6.05x102 17.9 3.03x102 41.7 5.96 (1) What is the half-life for the reaction starting at t-0 s? What is the half-life for the reaction starting at t 5.96 s? Does the half-life increase, decrease or remain constant as the reaction proceeds? (2) Is the reaction zero, first, or second order? (3) Based on these data, what is the rate constant for the reaction? M1s1

Explanation / Answer

1)starting at T = 0sec , a = 0.242 M

   half-concentration = 0.242/2 = 0.121 M, t = 5.96 sec

   half -life(T1/2) = 5.96 sec

starting at T = 5.96 sec , a = 0.121 M

half-concentration = 0.121/2 = 0.0605 M, t = 17.9 sec

   half -life = 17.9-5.96 = 11.94 sec

half life increases, as the reaction proceeds.

2)

t1/2 x (1/a^(n-1))

(t1/2)1/(t1/2)2 = (a2/a1)^(n-1)

(5.96/11.94) = (0.121/0.242)^(n-1)

n = 2

   n = order of reaction,

so that, it is a second order reaction.

second order kinetics.

K2 = x/t*(a-x)*a

k2 = ? M-1.s-1

a = initial concentration = 0.242 M

a-x = concentration after time,t = 0.121 M

t = time = 5.96 sec

3) K2 = (0.121/(5.96*(0.242-0.121)*0.242))

   = 0.693 M-1.S-1

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