Question

For the first order thermal decomposition reaction, the following data were obtained:

Time / sec               Totalpressure / atm

0                              0.30

300                          0.50

Calculate the rate constant

(Given: log 2 = 0.301, log3 = 0.4771, log 4 = 0.6021)

Answer 1

Given :

P_i = 0.30 atm

P_t = 0.50 atm

C₂H₅Cl_(g)→C2H_4(g)+HCl_(g)

  P_i    0    0    (At t = 0 sec)

P_i-x   x    x     (At t = 300 sec)

So,

P_i - x + x + x = P_t

0.3+x = 0.5

x = 0.2

Then, P_i - x = 0.3 - 0.2 = 0.1 atm

For first order reaction,

`k=2.303/tlog(P_i/(P_i-x))`

`=2.303/tlog(0.3/0.1)`

`=(2.303xxlog3)/300=(2.303xx0.4771)/300`

 k = 0.0037 s^-1