SF4 ---> SF2 + F2
rate constant (k) = .011 l/molxS [SF4]2
How many minutes will it take for the concentration of SF4 to be reduced from 2.5 M to .25 M?
I said this was a 2nd order reaction and used :
(1/final)= kt + (1/initial) and solved for t.
the answer should be 5.5. I am not getting that answer. what am I doing wrong?
That is correct but if they want the answer in minutes you have to divide by 60. that equation gives you the (seconds) that it will take. when you divide by 60 it will give you the minutes.
1/.25M=.011(t)+1/2.5M
subtract (1/2.5) from both sides
3.6=.011(t)
divide both sides by .011
t=327.27s
they ask for minutes so divide this number by 60
t=327.27/60 t=5.45 or 5.5
To solve this problem, you correctly identified that it is a second-order reaction. The integrated rate law for a second-order reaction is:
1/[SF4]t = kt + 1/[SF4]0
where [SF4]t is the concentration of SF4 at time t, [SF4]0 is the initial concentration of SF4, k is the rate constant, and t is the time.
Rearranging the equation, we have:
1/[SF4]t - 1/[SF4]0 = kt
Plugging in the given values:
1/0.25 - 1/2.5 = (0.011 L/mol·s) * t
Simplifying further:
4 - 0.4 = 0.011t
3.6 = 0.011t
To solve for t, divide both sides by 0.011:
t = 3.6 / 0.011 ≈ 327.27 s
However, you mentioned that the answer should be in minutes. To convert seconds to minutes, divide the result by 60:
t ≈ 327.27 s / 60 ≈ 5.45 min
So, the concentration of SF4 will be reduced from 2.5 M to 0.25 M in approximately 5.45 minutes, which is consistent with the expected answer of 5.5 minutes.
To solve this problem, you correctly identified it as a second-order reaction. However, it seems like you made a mistake while applying the integrated rate law equation for a second-order reaction.
The integrated rate law equation for a second-order reaction is given as:
1/[A]t = kt + 1/[A]0
where [A]t represents the final concentration of the reactant, [A]0 represents the initial concentration, k is the rate constant, and t is the time.
In this case, we need to determine the time (t) it takes for the concentration of SF4 to decrease from 2.5 M to 0.25 M.
Let's substitute the known values into the equation:
1/0.25 M = (0.011 L/mol·s) × t + 1/2.5 M
Simplifying the equation, we get:
4 = (0.011 L/mol·s) × t + 0.4
Rearranging the equation to isolate t, we have:
(0.011 L/mol·s) × t = 4 - 0.4
(0.011 L/mol·s) × t = 3.6
Now divide both sides of the equation by 0.011 L/mol·s to solve for t:
t = 3.6 / 0.011 L/mol·s
Calculating this expression, we get:
t ≈ 327.27 seconds
To convert seconds to minutes, divide by 60:
t ≈ 327.27 seconds / 60 seconds/minute
t ≈ 5.46 minutes
So, the correct answer is approximately 5.46 minutes. The value of 5.5 you mentioned may be rounded up from 5.46.