For the reaction 4A(g) + 3B(g) ---> 2C(g), the following data were obtained at constant temperature. Determine the value of k for the reaction.

Question

For the reaction, 4 A(g) + 3 B(g) => 2 C(g), the following data were obtained at constant temperature. 

Experiment	Initial A conc., mol/L	Initial B conc., mol/L	Initial Rate, M/min
1	0.200	0.150	5.00
2	0.400	0.150	20.0
3	0.200	0.300	20.0
4	0.400	0.300	80.0

Determine the value of k for the reaction. Give that answer to 3 significant figures in 1.23E4 format.

Answer 1

Compare exp. 1 and 2. [A] doubles and [B] remains constant. Rate increases 4-fold. This tells you that it is second order with respect to A.

Compare exp. 1 and 3. [A] remains constant and [B] doubles. Rate increases by 4-fold. This tells you this it is second order with respect to B

Write the rate equation: rate = k[A]²[B]²

plug in any rate and solve for k. I'll use rate from exp. 1:

5.00 M/min = k(0.200)²(0.150)² = 0.0009k

k = 5.00/0.0009 = 5556 = 5.56x10³ M^-3/min