# Orders for rate of reaction Help!Watch

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#1
https://imgur.com/vYThsbq

I'm stuck on how I could deduce what the order is with respect to reactant D.

I've tried using the data from the table, where it shows the values of initial conc of both D and E for a number of exp's

For order with respect to E, I got the answer to be 2nd order because provided that the conc values of D to be kept constant when comparing the exp's of 2 and 3, I see that the conc doubles but the rate quadruples hence indicating that order must be 2.

I think I got order with respect to E to be right which is 2 but I can't seem to know how to find order with respect to D. I've always thought that to find order for D then the conc value's for E has to be the same for a pair of experiments but this is not the case as I see there isn't an option for one in the given table.

I also somehow need to show my working out too?

If anyone could help me find the order with respect to D that would be great! Thanks!
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1 year ago
#2
order wrt D is first order.
you don't need to show working. 2 marks are for 2 correct answers.

find out what effect the change in [E] had on rate from 1 to 2
find the effect the change in [D] had on rate
hence deduce order
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#3
(Original post by BobbJo)
order wrt D is first order.So
you don't need to show working. 2 marks are for 2 correct answers.

find out what effect the change in [E] had on rate from 1 to 2
find the effect the change in [D] had on rate
hence deduce order
So from what I can see is when comparing for experiment 1 and 2, the change in [E] had the rate go down to 70% or the rate was reduced to a scale factor of 0.30 since '1.16 x 10^-2 / 3.92 x 10^-2 = 0.30 (2dp)'

In change in [D] what 2 expt's are we comparing with to see the effect in rate? I thought we could only look at [D] provided that [E] has no change in a set of 2 expt's? However there appears to be none in the table??
Last edited by Yatayyat; 1 year ago
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1 year ago
#4
(Original post by Yatayyat)
So from what I can see is when comparing for experiment 1 and 2, the change in [E] had the rate go down to 70% or the rate was reduced to a scale factor of 0.30 since '1.16 x 10^-2 / 3.92 x 10^-2 = 0.30 (2dp)'

In change in [D] what 2 expt's are we comparing with to see the effect in rate? I thought we could only look at [D] provided that [E] has no change in a set of 2 expt's? However there appears to be none in the table??
it is easier to compare when it is not fractional
you can look at expts where both [reactant] change as below

here is how I would approach it
we have established that rxn is 2nd order wrt E.

using 1 and 2:
from 1 to 2, ratio of rates = 3.92 / 1.16 = 3.4
ratio of [E] = 8.73 / 5.81 = 1.5
[E] increases by 1.5 x causes rate to increase by 1.5^2 = 2.25 times
so change in [D] caused rate to increase by 3.4/2.25 = 1.5 times
ratio of [D] = 8.73/5.81 = 1.5
so increasing [D] by 1.5 x caused rate to increase by 1.5 x.
hence first order

using 1 and 3:
comparing 1 to 3
rate increased by 13.5 x
[E] increased by 3 x so increase in [E] caused rate to increase by 9 x
so change in [D] caused rate to increase by 13.5 / 9 = 1.5 x
[D] increased by 1.5 x
so first order
Last edited by BobbJo; 1 year ago
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#5
(Original post by BobbJo)
it is easier to compare when it is not fractional
you can look at expts where both [reactant] change as below

here is how I would approach it
we have established that rxn is 2nd order wrt E.

using 1 and 2:
from 1 to 2, ratio of rates = 3.92 / 1.16 = 3.4
ratio of [E] = 8.73 / 5.81 = 1.5
[E] increases by 1.5 x causes rate to increase by 1.5^2 = 2.25 times
so change in [D] caused rate to increase by 3.4/2.25 = 1.5 times
ratio of [D] = 8.73/5.81 = 1.5
so increasing [D] by 1.5 x caused rate to increase by 1.5 x.
hence first order

using 1 and 3:
comparing 1 to 3
rate increased by 13.5 x
[E] increased by 3 x so increase in [E] caused rate to increase by 9 x
so change in [D] caused rate to increase by 13.5 / 9 = 1.5 x
[D] increased by 1.5 x
so first order
Yes I can see this more now. With the part where you indicate that an increase in [E] by 1.5 x causes rate to increase by 1.5^2, how is this right if multiplying rate in expt 1 by 2.25 gives 1.16 x 10^-1 * 2.25 = 2.61 x 10^-1
Shouldn't the 2.61 x 10^-1 be 3.92 x 10^-1 instead?

Also when you said the ratio of [D] is 8.73/5.81 (aren't these the values that are assigned to [E] ), shouldn't the ratio be 1.88/1.25, anyway both still give 1.5
0
1 year ago
#6
(Original post by Yatayyat)
Yes I can see this more now. With the part where you indicate that an increase in [E] by 1.5 x causes rate to increase by 1.5^2, how is this right if multiplying rate in expt 1 by 2.25 gives 1.16 x 10^-1 * 2.25 = 2.61 x 10^-1
Shouldn't the 2.61 x 10^-1 be 3.92 x 10^-1 instead?
You changed [D] too. changing [D] caused rate to change.

using 1 and 2:
from 1 to 2, rate increased by 3.92 / 1.16 = 3.4 times
[E] increased by 8.73 / 5.81 = 1.5 times
order wrt to E is 2nd order
[E] increasing by 1.5 x causes rate to increase by 1.5^2 = 2.25 times
but we also changed [D], the overall change in rate was 3.4 times,
[E] caused a change of 2.25 x
so change in [D] caused rate to increase by 3.4/2.25 = 1.5 times
(overall = 2.25 (due to change in [E]) x 1.5 (due to [D]) = 3.4 times)
[D] increased by 1.88/1.25 = 1.5x
change in [D] caused rate to increase 1.5 times
so increasing [D] by 1.5 x caused rate to increase by 1.5 x.
hence first order

Also when you said the ratio of [D] is 8.73/5.81 (aren't these the values that are assigned to [E] ), shouldn't the ratio be 1.88/1.25, anyway both still give 1.5
Yes sorry
Last edited by BobbJo; 1 year ago
0
#7
(Original post by BobbJo)
Yes sorry
Thank you I found this so helpful
0
1 year ago
#8
You... React bloody faster !
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