Quick Chemical kinetics question

[Link]

The rate constant for a certain reaction has the units concentration/time. What is the order of the raction?

A. 0
B. 1
C.2
D.3

My reasoning:

K = [A]^m x ^n

Since the concentration/time is to the power of one, both m and n must be one i think which give an overall order of one?... since if they were zero there would be no reaction?

 

[Sirus]

There is a formula for this.

$$k=\frac{\left(\frac{L}{mol}\right)^{\mbox{order}-1}{\mbox{units of time}}$$

EDIT: for some reason the latex is not working.

k=[(L/mol)^{order - 1}]/(units of time)

 

[Link]

Do you mean that in order to have the unit as concentration/time, it should be:

K = C^(2-1)/t

which gives the answer C?

 

[Sirus]

Use the formula. If K must be in units of concentration over time, what must the order be in the formula?

 

[Sirus]

Here's the fixed latex:

$$k=\frac{\left(\frac{L}{mol}\right)^{\mbox{order}-1}}{\mbox{units of time}}$$

 

[Link]

So its C i suppose


Thank you for the help!

 

[Sirus]

How did you get C? That's incorrect.

 

[Link]

if the unit is concentration/time it should be:

(Concentration^1) = K
-------------------
time


So i think it's :

[Concentration]^[2] - 1
------------------------ =
time

(Concentration^1)
------------------- = K
time


the order should be: [2]

Thats how i reasoned.

 

[Sirus]

Review the formula. What are the units for concentration? What are the units in the formula?

 

[Gokul43201]

The rate constant for a certain reaction has the units concentration/time. What is the order of the raction?

A. 0
B. 1
C.2
D.3

My reasoning:

K = [A]^m x ^n

Since the concentration/time is to the power of one, both m and n must be one i think which give an overall order of one?... since if they were zero there would be no reaction?

From your reasoning above where would you get the dimensions of time from ? The error is in that your equation is for the rate, not the rate constant.

You solve this problem, you can either remember the formula provided by Sirus, or simply work it out from first principles. The order n, of the reaction determines the rate law :

$$rate = -\frac {dX}{dt} = kX^n$$ where X is a concentration.

So $$-k = X^{-n} \frac {dX}{dt}$$

So the dimensions of k will be $$\frac {[X^{1-n}]}{[T]}$$

In this particular case, the fact that k has the same units as the rate, makes it all the more easy and negates the need to go beyond the first step.

 

[GCT]

Just focus on the equation rate=kX^n, the units for the rate will always be in terms of concentration/T. The right side of the equation, besides k, will be in terms of concentration, concentration squared, etc...depending on the order number (you should be able to see this). Thus if we have k in terms of concentration/time (M/s), and rate=concentration/time (M/s), dividing the rate by k will give you 1, meaning zero order.