Question

QUESTION 3 [10 MARKS] a) Isobutane is used as a feedstock in the petrochemical industry, for example in the synthesis of isooctane. When 3.0 g of isobutene is heated to 400 C, it will change into butene. Table 2 shows the data that obtained in one experiment. After 25 minutes the mass of unreacted isobutene is remaining is found to be 0.375 g. Table 2: Experiment data Time Concentration of butene (min) (mol/L) 1.5 x103 10 1.24 x103 20 1.00 x103 30 0.83 x103 1) Plot the data to determine the reaction order (7 Marks) ii) From the graph obtained, calculate the rate of constant. (3 Marks)

Answer 1

time(min Zero order conc (M) conc (M) y -22.5x1480 R2 0.991 1500 0 1600 10 1240 1400 20 1000 1200 30 830 1000 800 600 400 200 10 15 20 25 30 35 O O

time(min FIRST ORDER y-0.008x+3.178 R2 0.999 log conc log conc 0 3.18 3.2 10 3.09 3.15 20 30 2.92 3.1 3.05 3 2.95 2.9 0 5 10 15 20 25 30 35 n

y 2E-05x+0.000 R2 0.993 time(min 1/conc SECOND ORDER 1/conc (/M) |(/M) 0.00067 0 0.0014 0.00081 10 0.0012 20 0.001 0.001 0.0012 30 0.0008 0.0006 0.0004 0.0002 0 10 15 20 35 30 25

From the above kinetic graph the one with perfect straight line is first order graph whose R² value is 0.999 and equation is

y = -0.008x+3.178

ln [A] = -kt+ ln [A]o

Y - axis = ln [A] and X-axis = time (mins)

Hence slope = m = - rate constant = -k = -0.008

Rate constant, k = 0.008 /sec