The following data were measured for the reaction BF3( g )+NH3( g )F3BNH3( g ):
ID: 892514 • Letter: T
Question
The following data were measured for the reaction BF3(g)+NH3(g)F3BNH3(g):
Experiment
[BF3](M)
[NH3](M)
Initial Rate(M/s)
1
0.250
0.250
0.2130
2
0.250
0.125
0.1065
3
0.200
0.100
0.0682
4
0.350
0.100
0.1193
5
0.175
0.100
0.0596
What is the overall order of the reaction?
What is the value of the rate constant for the reaction?
What is the rate when [BF3]= 0.170 M and [NH3]= 0.560 M ?
Experiment
[BF3](M)
[NH3](M)
Initial Rate(M/s)
1
0.250
0.250
0.2130
2
0.250
0.125
0.1065
3
0.200
0.100
0.0682
4
0.350
0.100
0.1193
5
0.175
0.100
0.0596
Explanation / Answer
Let, rate of reaction be,
rate = k[BF3]^x.[NH3]^y
where,
x and y are order with respect to BF3 and NH3 in the reaction
Comparing experiment 1 and 2, the concentration of [BF3] is same so gets cancelled out, we get
rate1/rate2 = 0.2130/0.1065 = (0.250/0.125)^y
taking log on both sides,
log(2) = ylog(2)
y = 1
So order of reaction is 1 with respect to [NH3]
Now, taking experiments 4 and 5, concentration of NH3 is same.
the initial rate of reaction doubles (from 0.0596 to 0.1193) when concentration of [BF3] doubles from 0.175 M to 0.350 M, so the order with respect to BF3 is 1.
The overall rate = 1 + 1 = 2
The rate of reaction will be thus,
rate = k[BF3][NH3]
with k being the rate constant
take experiment 1,
k = 0.2130/(0.250 x 0.250) = 3.408 M-1.s-1
rate when [BF3] = 0.170 M and [NH3] = 0.560 M
rate = 3.408 x 0.170 x 0.560 = 0.324 M.s-1
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