Ethyl iodide (c2h5i) decomposes at a certain temperature in the gas phase as follows: c2h5i(g) → c2h4(g) + hi(g) from the following data determine the order of the reaction and the rate constant. time (min) [c2h5i] (m) 0.0 2.00 15.0 1.82 30.0 1.64 48.0 1.42 75.0 1.10

Zero order

Explanation:

Looking at the data we can note a linear dependence between concentration and time.  

Time   Conc.

0          2

15         1.82

30        1.64

48        1.42

75        1.10

In the first 15 min it was consumed 2-1.82=0.18. So the rate is

From 15 to 30 min (it has passed 15 min) is consumed 1.82-1.64=0.18, so as in the previous calculation the rate is .

From 30 to 48  (it has passed 18 min)the rate is  

From 48 to 75  (it has passed 27 min) the rate is  

So these results suggest that despite of the ever minor concentration of the reactant the rate is ever the same. Hence the reaction rate could be expressed as that is, the reaction is the zero order respect to C2H5I since it is not depending on concentration of C2H5I.