Question

The following questions refer to the gas phase decomposition of ethylene chloride

C2H5Cl→ products

Experiment shows that the decomposition is first order. The following data show kinetics

information for this reaction.

Time (s)               1.0       2.0

ln [C2H5Cl] (M)    -1.625    -1.735

What is the rate constant for this decomposition if [C2H5Cl] is 0.20M?

What was the initial concentration of the ethylene chloride? K=0.12

What would the concentration be after 4.0 seconds? based on previous question

Answer 1

To calculate the rate constant use the following expression:

ln [A] - In[A]o = - k t

here, ln [C2H5Cl] (M) at t means 1 sec    = -1.625

[C2H5Cl] 0 (M)   = 0.20 M

Time, t = 1.0 s

Then;

-1.625 – In 0.20 = - k *1 s

-1.625- (1.61)= - k s

- 0.015 = -k s

k = 0.015 s-1

To calculate the initial concentration use the following expression:

ln [A] - In[A]o = - k t

here, ln [C2H5Cl] (M) at t means 1 sec    = -1.625

[C2H5Cl] 0 (M)   = ? M

Time, t = 1.0 s

K = 0.12

Then;

-1.625 – In [A]o = - 0.12 *1 s

– In [A]o = 1.505

[A]o = e^-1.505

[A]o = 0.22 M

To calculate the concentration after 4 sec use the following expression:

ln [A] - In[A]o = - k t

here, [C2H5Cl]0 (M)    = 0.22 M

[C2H5Cl] t (M)   = ? M at 4 sec

Time, t = 4.0 s

K = 0.12

Then;

In[A] – In (0.22)= - 0.12* 4

In[A]-(-1.51) = -0.48

In[A] +1.51 = -0.48

In[A] = -1.99

[A] = e^-1.99

[A] = 0.136 M