In a study of the decomposition of ammonia on a tungsten surface at 1100 °C the

Question

In a study of the decomposition of ammonia on a tungsten surface at 1100 °C the following data were obtained: [NH3]. M 1.33x10-2 6.65x10-3 443 3.33x10-3 663 1.67x10-3 seconds Hint: It is not necessary to graph these data The observed half life for this reaction when the starting concentration is 1.33x10- M is concentration is 6.65x10 Mis s and when the starting The average rate of disappearance of NH3 from t = 0 s to t = 443 s is M s The average rate of disappearance of NH3 from t = 443 s to 663 s is M s-1 Based on these data, the rate constant for this order reaction is

Explanation / Answer

Q1

half life --> time required to achieve 50%

time --> (443-0) = 443 seconds

Q2.

avg. rate from 0 to 443

dC/dt = (6.65*10^-3 - 1.33*10^-2) /(443-0) = -0.0000150 M/s

Q3

avg. rate from 443 to 663

dC/dt = (3.33*10^-3 - 6.65*10^-3) /(663-443) = --0.0000150 M/s

Q4

based on this data... we can see that rate will NOT change, therefore, this must be zero order

Rate = k

then

k = 0.0000150 M/s

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