Question

Question # 3: Algorithmic Questions.   

A. A particular first-order reaction has a rate constant of 1.35 ×102 s-1 at 25.0 °C. What is the magnitude of k at 75.0 °C if Ea = 85.6 kJ/mole?

B. The rate constant for a second-order reaction is 0.13 M-1s-1. If the initial concentration of reactant is 0.26 mole/L, how much it will take for the concentration to decrease to 0.13 mole/L?

Answer 1

A. Using Arrhenius equation,

ln(k2/k1) = Ea/R[1/T1 - 1/T2]

with,

k1 = 1.35 x 10^2 s-1

k2 = ?

T1 = 25 + 273 = 298 K

T2 = 75 + 273 = 348 K

Ea = 85.6 kJ/mole

R = gas constant

we get,

ln(k2/1.35 x 10^2) = 85600/8.314[1/298 - 1/348]

rate constant at 75 oC k2 = 1.93 x 10^4 s-1

B. For a second order reaction,

1/[A] = 1/[Ao] + kt

with,

[A] = 0.13 mole/L

[Ao] = 0.26 mole/L

k = 0.13 M-1.s-1

t = ?

we get,

1/0.13 = 1/0.26 + 0.13 x t

So time taken to reach a concentration of 0.13 mole/L would be t = 29.58 s