Determining the rate constant when given trials

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Priscilla Okaiteye
Posts: 61
Joined: Tue Nov 21, 2017 3:02 am

Determining the rate constant when given trials

Postby Priscilla Okaiteye » Tue Mar 12, 2019 4:20 am

For questions like finding the order of the reactant when you are given trials, I know the rule is to use two trials that keep the other reactants constant and have the reactant you are focusing on changing, but how come in som e questions that is not the case?

For example in 15.17 part a). The solutions manual says to use two trials that do not have the other reactants constant then it tells you to divide them instead. I am confused and just need some clarification.

Camille Marangi 2E
Posts: 60
Joined: Fri Sep 28, 2018 12:26 am

Re: Determining the rate constant when given trials

Postby Camille Marangi 2E » Tue Mar 12, 2019 11:16 am

If you could post the problem that would be a lot more helpful but usually if you have to use two trials that are not kept constant, you most likely will know the order of one of the reactants whose trials you are using. Then, because you know the order of one reactant you can see how much that specific reactant changed the rate and then whatever change remains will help you determine the order of the other changed reactant. Hope this was helpful in any way!

Ethan Baurle 1A
Posts: 33
Joined: Fri Sep 28, 2018 12:19 am

Re: Determining the rate constant when given trials

Postby Ethan Baurle 1A » Tue Mar 12, 2019 11:18 am

For this particular question, you are using ones where concentrations aren't all constant because on of the reactants is zero order and does not effect the rate law. As far as dividing things goes, that is just to show the ratio of the concentration in one reaction to that of another and then compare the rates of that. You just have to take the ratio of the reactant thats concentration is changing (everything else will cancel out) but the solution manual is showing all the concentrations to clarify that one reactant is zero order and thus it doesn't matter that its concentration is changing as well.

Lynsea_Southwick_2K
Posts: 55
Joined: Fri Sep 28, 2018 12:25 am

Re: Determining the rate constant when given trials

Postby Lynsea_Southwick_2K » Wed Mar 13, 2019 8:16 am

15.17 The following rate data were collected for the reaction 2A(g) + 2B(g) +C(g) -> 3G(g) + 4F(g):

Initial concentration (mmol.L^-1)
Experiment [A]v0 [B]v0 [C]v0 Initial rate((mmol G).L^-1.s^-1)
1 10. 100. 700. 2.0
2 20. 100. 300. 4.0
3 20. 200. 200. 16
4 10. 100. 400. 2.0
5 4.62 0.177 12.4 ?
a) what is the order for each reactant and the overall order of the reaction?
b) Write the rate law for the reaction.
c) Determine the reaction rate constant.
d) Predict the initial rate for Experiment 5.


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