Arkansas State University Department of Chemistry and Physics

Answers

Kinetics

1 Write the rate expression in terms of D[reactant]/Dt  and  D[product]/Dt:

rate  = - D[N₂]/Dt    =   - D[H₂]/3Dt   =  D[NH₃]/2Dt

2 Determine
a) the order of each reactant: 1st order in A; zero order in B
b) the order of the reaction: overall reaction is 1st ordered
c) write the rate law: rate = k[A]
d) calculate the rate constant, k: k = 1.75 x 10^-2/s

3a. The decomposition of A₂B₃ is second order with a k = 6.5 x 10^-5 M^-1s ^-1 at 25^oC.  If the initial concentration is 0.50 M, the concentration after 3 min is: 0.497 M

b. The half-life for the reaction in question 3a is: 3.08 x 10⁴ s

4. The decomposition of AB is first order with a k = 2.3 x 10^-7 s^-1 at 45^oC.  If the initial concentration is 0.25 M,  the concentration after 2.3 min is: 0.25 M

b. The half-life for the reaction in question 4a is: 3.01 x 10⁶ s

5a. The concentration of reactant after 2.5 minutes if the inital concentration was 0.100 M and k = 6.93 x 10^-3 s^-1 for a first order reaction is: 0.0354 M

b. The half-life is: 100 s

6. For the first order reaction:

  SO₂Cl₂      ----->     SO₂   + Cl₂

 How long will it take to reach 0.31 x 10^-3 M if the inital concentration was 1.25 x 10^-3 M and k = 0.17/hr? 8.2 hrs

7. For the second order reaction   A -----> B (k = 1.5 x 10^-2/Ms),

 a) if the initial concentration of A is 0.10M, the concentration of A after 4 min is: 0.074 M

 b) the half-life is: 667 s