Question

. A reaction in this experiment is started when 3.00 mL of 0.100 M t-butyl chloride is diluted to a final volume of 10.0 mL. After 150 sec, t1/10 has been reached.

a. What is the concentration of t-butyl chloride (molarity) at the start of the reaction?

b. What is the value of the rate constant (k) if the reaction is first order?

c. What is the value of the rate constant (k) if the reaction is second order?

2. The reaction in #1 is repeated, but this time 6.00 mL of 0.100 M t-butyl chloride is diluted to a final volume of 10.0 mL.

a. Using the k value from your answer to #1b, what t1/10 should be expected if the reaction is first order?

b. Using the k value from your answer to #1c, what t1/10 should be expected if the reaction is second order?

Answer 1

1(a).

conc. of t-butyl chloride initial vol. = final conc. final vol.

final conc. = 30.1/10

               =0.03 M

1(b).

K=2.303log(a/a-x)/t                   where a is initial conc. and x is amount of 'a' consumed i.e- a/10

K=2.303log(10/9)/150

K=7.02410^-4 sec^-1

1(c).

In second order:

1/a_t = Kt+ 1/a₀                       where a_t is conc. at time t that is 9a/10 and a₀ is initial conc.

10/9a = K150 + 1/a         where a=0.03M

K=0.0246 M^-1sec^-1

2(a).

In first order reaction t_1/10 does not depend on initial concentration, so 't_1/10' will remain same.

2(b).

In second order kinectics, time of reaction varies inversely with initial concentration

So,new t_1/10 will be half of initial t_1/10 (as concentration has been doubled)

i.e. t_1/10=150/2 = 75 sec