The integrated rate laws for zero-, first-, and second-order reaction may be arranged such that they resemble the equation for a straight line,y=mx+b.
1.) The reactant concentration in a zero-order reaction was 6.00×10−2M after 165 s and 3.50×10−2Mafter 385 s . What is the rate constant for this reaction?
2.)What was the initial reactant concentration for the reaction described in Part A?
3.)The reactant concentration in a first-order reaction was 6.70×10−2
M after 40.0 s and 2.50×10−3Mafter 95.0 s . What is the rate constant for this reaction?
4.)The reactant concentration in a second-order reaction was 0.850
M after 255 s and 3.40×10−2M after 860 s . What is the rate constant for this reaction?
Order | Integrated Rate Law | Graph | Slope |
0 | [A]=−kt+[A]0 | [A] vs. t | −k |
1 | ln[A]=−kt+ln[A]0 | ln[A] vs. t | −k |
2 | 1[A]= kt+1[A]0 | 1[A] vs. t | k |
According to the equations on your table, we can actually calculate all that.
For a zero order reaction, the equation to use would be:
A = Ao - kt
We already know the concentrations after some time, so the expression for a linear equation to get the slope is:
k = A2 - A1 / t2 - t1
We have both concentrations to a given time so:
k = 0.035 - 0.06 / 385 - 165
k = -1.136x10-4 M/s
Now that we have the constant, we can calculate the innitial concentration:
A = Ao - kt
Ao = A + kt
Ao = 0.06 + (-1.136x10-4)*(165)
Ao = 0.04125 M
As for a first order reaction the procedure is exactly the same but using the equation for a first order:
lnA = lnAo - kt
k = lnA2 - lnA1 / t2 - t1
k = ln(0.0025) - ln(0.067) / 95-40
k = -0.0598 s-1
For the last question use the second order reaction:
k = 1/A2 - 1/A1 / t2 - t1
Solve for k, replacing the values.
Hope this helps
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