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# Kinetics General Q watch

1. Hi

I just wanted to know that in order to calculate the initial rate, we need the orders of each species as well as the initial concentrations of each of the species. But do we not need the value of k? In the above Q, I don't need to use k to work out initial rate, why not?
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2. (Original post by ps1265A)

Hi

I just wanted to know that in order to calculate the initial rate, we need the orders of each species as well as the initial concentrations of each of the species. But do we not need the value of k? In the above Q, I don't need to use k to work out initial rate, why not?
You know they're both first order.

So if the concentration of NaOH has tripled, and A has doubled compared to experiment 1, then the rate will be 6x faster.
3. (Original post by L'Evil Fish)
You know they're both first order.

So if the concentration of NaOH has tripled, and A has doubled compared to experiment 1, then the rate will be 6x faster.
But I'm trying to say, say if we have a general statement: As concentration of A and B doubles, rate quadruples.

This tells us that they're both order 1. However, this takes into no consideration of K. Do we just ignore K here? I thought K also has an effect on rate?
4. (Original post by ps1265A)
But I'm trying to say, say if we have a general statement: As concentration of A and B doubles, rate quadruples.

This tells us that they're both order 1. However, this takes into no consideration of K. Do we just ignore K here? I thought K also has an effect on rate?
That isn't true, one could be second order and the other 0 order. But their overall rate is Order 2.

K is already taken into account it's a constant and you're just looking at proportions. K won't change between experiments 1, 2, 3 and 4 if conditions are kept constant so you don't need to calculate it.
5. (Original post by L'Evil Fish)
That isn't true, one could be second order and the other 0 order. But their overall rate is Order 2.

K is already taken into account it's a constant and you're just looking at proportions. K won't change between experiments 1, 2, 3 and 4 if conditions are kept constant so you don't need to calculate it.
OK thanks!

In the above example, I just figured out I needed to work out k (1/3) to work out initial rate for Expt 4

And also does concentration affect the order of the reaction? (Taking into account that one of the species is in excess)
6. (Original post by ps1265A)
OK thanks!

In the above example, I just figured out I needed to work out k (1/3) to work out initial rate for Expt 4

And also does concentration affect the order of the reaction? (Taking into account that one of the species is in excess)
You can calculate k from it, but it isn't needed.

It won't affect the order, but it'll affect the amount produced.
7. (Original post by L'Evil Fish)
You can calculate k from it, but it isn't needed.

It won't affect the order, but it'll affect the amount produced.
Both species are order 1, if we times them together, we don't get the answer?

But say if we increase the concentration of NaOH all the way to 2.00; it may become 0 order as it doesn't affect the rate anymore. Only [A] is the limiting factor.

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