Homework Help: chemistry

Posted by Evets on Tuesday, January 29, 2008 at 4:32pm.

1)
The activation energy of a certain reaction is 35.3 kJ/mol. At 20 degrees C, the rate constant is 0.0130 s^-1. At what temperature would this reaction go twice as fast?
Answer in units of degrees Celsius.

i think the answer is around 34, but i keep in getting it screwed up.

2)
Consider the following multistep reaction:

C + D <> CD (fast)
CD + D > CD2 (slow)
CD2 + D > CD3 (fast)
C + 3D > CD3 (overall)

determine the rate law for the overall reaction

Answer should be in k[A][B]^2 format

I know the overall reaction has much to do with the slow reaction, but i dont get how to incorporate that into its proper format based on its order

3)

The reactant concentration in a zero-order reaction was 0.100 M after 125 s and 1.50×10−2 M after 385 s. What is the rate constant for this reaction?
What was the initial reactant concentration for the reaction?

I found the rate constant to be 3.27 x 10^-4 M/s, but im having trouble finding initial reactant concentration...

an equation that mite help..
[A]= - kt + [A]0

[A]0 is the initial reactant rate i beleieve.. i thinks...

chemistry - DrBob222, Tuesday, January 29, 2008 at 4:44pm
1)
The activation energy of a certain reaction is 35.3 kJ/mol. At 20 degrees C, the rate constant is 0.0130 s^-1. At what temperature would this reaction go twice as fast?
Answer in units of degrees Celsius.

i think the answer is around 34, but i keep in getting it screwed up.

How are you solving it? Post your work and I'll try to find the error. You should be using the Arrhenius equation.
Also, make sure activation energy is J/mol. Also make sure you are using temperature in Kelvin.
chemistry - DrBob222, Tuesday, January 29, 2008 at 5:06pm
3)

The reactant concentration in a zero-order reaction was 0.100 M after 125 s and 1.50×10−2 M after 385 s. What is the rate constant for this reaction?
What was the initial reactant concentration for the reaction?

I found the rate constant to be 3.27 x 10^-4 M/s, but im having trouble finding initial reactant concentration...

an equation that mite help..
[A]= - kt + [A]0

[A]0 is the initial reactant rate i beleieve.. i thinks...

Can't you simply take the initial equation you had, which is,
[A] = [A]_o - kt (that's how you found k is it not?), then
substitute A = 0.1 and substitute your value of k, and 125 for t, then solve for [A]_o? You could also use 1.5 x 10^-2 for (A) and 385 for t and your value of k and get the same value although I didn't try it. Check my thinking. I found about 0.14 M or so using the first suggetion above.

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