What is the the rate constant for this first order reaction is __________ s-1?

Question

The reaction A (aq) B (aq) is first order in [A]. A solution is prepared with [A] = 1.22 M. The following data are obtained as the reaction proceeds:
_____________________________
Time (s) | 0 | 6 | 12 | 18 |
[A] (M) |1.22 | 0.61 | 0.31 | 0.15 |
|
The rate constant for this reaction is __________ s-1.

The given answers are: 0.23, 1.0, 0.17, 0.12 or -0.12.

Answer 1

Use any two sets of data and plug it into the equation:

ln ([A]o/[A]t) = kt

Using the first two, we get:

ln (1.22/0.61) = 6k
0.693 = 6k
k = 0.116 s^-1

Using any other combination of times and concentrations will give you the same answer.

Answer 2

It is the gradient of the line of M against t.

According to MS Excel this value is a curve =O. You sure it is not second order?

The gradient comes out as M = 1.226e-0.11t