In a study of the decomposition of ammonia on a platinum surface at 856 °C NH3 1

Question

In a study of the decomposition of ammonia on a platinum surface at 856 °C

NH3 1/2 N2 + 3/2 H2

the following data were obtained:

[NH3], M 2.45E-3 1.23E-3 6.15E-4 3.08E-4
seconds 0 998 1.50E3 1.75E3

Hint: It is not necessary to graph these data.

(1)
The observed half life for this reaction when the starting concentration is 2.45E-3 M is
s and when the starting concentration is 1.23E-3 M is s.

(2)
The average rate of disappearance of NH3 from t = 0 s to t = 998 s is M s-1.

(3)
The average rate of disappearance of NH3 from t = 998 s to t = 1.50E3 s is M s-1.

(4)
Based on these data, the rate constant for this order reaction is M s-1.

Explanation / Answer

NH3 --> 1/2 N2 + 3/2 H2

The data is
seconds 0 : 2.45 X 10^-3

998 :1.23X 10^-3

1.50X 10^3 : 6.15X 10^-4

1.75X 10^3 : 3.08X 10^-4

1) question is not clear

2) The average rate of disappearance of NH3 from t = 0 s to t = 998 s is M s-1.

RAte = change in conce / time = 2.45 X 10^-3 -1.23X 10^-3 / 0-998 = -12.2 X 10^-7M s-1.

3) RAte = change in conce / time = 1.23X 10^-3 - 6.15X 10^-4 /-998 - 1500 =0.615 X 10^-3 / 502 = 12.2 X 10^-7

4) rate = K [conc ] = 12.2 X 10^-7 = K X [1500]

K = 12.2 X 10^-7 / 1500 = 81.3 X 10^-9

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