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pls can someone explain why B is 2nd order? I thought it was 0?

i found that A is 1st order, so for B i looked at experiment 2 and 3, i looked at the effect A also had on the rate since both A and B were changing, i found the new rate with A was 1.8x10-5 when i did 0.90x2 because A is first order? then i divided this new rate by the rate they have given in experiment 3= 7.20x10-5 and i got 2.5x10-11, so i assumed this meant B is 0 order? is my working out wrong? pls can somoene show me how im supposed to do this

i found that A is 1st order, so for B i looked at experiment 2 and 3, i looked at the effect A also had on the rate since both A and B were changing, i found the new rate with A was 1.8x10-5 when i did 0.90x2 because A is first order? then i divided this new rate by the rate they have given in experiment 3= 7.20x10-5 and i got 2.5x10-11, so i assumed this meant B is 0 order? is my working out wrong? pls can somoene show me how im supposed to do this

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pls can someone explain why B is 2nd order? I thought it was 0?

i found that A is 1st order, so for B i looked at experiment 2 and 3, i looked at the effect A also had on the rate since both A and B were changing, i found the new rate with A was 1.8x10-5 when i did 0.90x2 because A is first order? then i divided this new rate by the rate they have given in experiment 3= 7.20x10-5 and i got 2.5x10-11, so i assumed this meant B is 0 order? is my working out wrong? pls can somoene show me how im supposed to do this

**usernamenew**)pls can someone explain why B is 2nd order? I thought it was 0?

i found that A is 1st order, so for B i looked at experiment 2 and 3, i looked at the effect A also had on the rate since both A and B were changing, i found the new rate with A was 1.8x10-5 when i did 0.90x2 because A is first order? then i divided this new rate by the rate they have given in experiment 3= 7.20x10-5 and i got 2.5x10-11, so i assumed this meant B is 0 order? is my working out wrong? pls can somoene show me how im supposed to do this

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(Original post by

post question

**BobbJo**)post question

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(Original post by

www.alevelrevisioncards.co.uk has great resources to use for exam preparation

**MathsGod100**)www.alevelrevisioncards.co.uk has great resources to use for exam preparation

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#7

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ive posted it, sorry took me a while

**usernamenew**)ive posted it, sorry took me a while

our rate equation is of the form

rate = k [A][B]

^{n}

use 1 and 3

from 1: 0.45 x 10^-4 = k x 0.15 x 0.24^n - (A)

from 3: 7.2 x 10^-4 = k x 0.6 x 0.48^n - (B)

eqn B/eqn A gives

7.2x10^-4/(0.45x10^-4)= (0.6 x 0.48^n)/(0.15 x 0.24^n)

we have eliminated k

now solve for n,

n = 2

order is 2nd order wrt B

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#8

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thank u

**usernamenew**)thank u

logic method

from 2 to 3

[A] doubled

this causes rate to double

but in fact rate in 3 is x8 the rate in 2

so change in concentration of B caused rate to x4 (quadruple)

doubling in concentration of B causes rate to x4

so order wrt B is 2nd order

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(Original post by

mathematical method above

logic method

from 2 to 3

[A] doubled

this causes rate to double

but in fact rate in 3 is x8 the rate in 2

so

doubling in concentration of B causes rate to x4

so order wrt B is 2nd order

**BobbJo**)mathematical method above

logic method

from 2 to 3

[A] doubled

this causes rate to double

but in fact rate in 3 is x8 the rate in 2

so

**change in concentration of B caused rate to x4 (quadruple)**doubling in concentration of B causes rate to x4

so order wrt B is 2nd order

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#10

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thank u! i prefer this method, once i know that 0.90x10-5 x 2cubed = 7.20x10-2, how does this mean B is x4? is it because A is x2 so u do 8/2 = 4

**usernamenew**)thank u! i prefer this method, once i know that 0.90x10-5 x 2cubed = 7.20x10-2, how does this mean B is x4? is it because A is x2 so u do 8/2 = 4

rate changes only due to change in concentration

both concentration of A and B changed

we know from 2 to 3 rate x8

from 2 to 3, [A] doubled. order wrt A is first order. so doubling [A] doubled rate

overall change in rate is x8

since we know change in [A] caused rate to double, other changes in rate must be due to [B]

so change in concentration of B caused rate to x4

change in [A] -> x2

change in [B] -> x4

overall -> x8

hence doubling [B] quadruples rate

so order wrt B is 2nd order

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(Original post by

yes

rate changes only due to change in concentration

both concentration of A and B changed

we know from 2 to 3 rate x8

from 2 to 3, [A] doubled. order wrt A is first order. so doubling [A] doubled rate

overall change in rate is x8

since we know change in [A] caused rate to double, other changes in rate must be due to [B]

so change in concentration of B caused rate to x4

change in [A] -> x2

change in [B] -> x4

overall -> x8

hence doubling [B] quadruples rate

so order wrt B is 2nd order

**BobbJo**)yes

rate changes only due to change in concentration

both concentration of A and B changed

we know from 2 to 3 rate x8

from 2 to 3, [A] doubled. order wrt A is first order. so doubling [A] doubled rate

overall change in rate is x8

since we know change in [A] caused rate to double, other changes in rate must be due to [B]

so change in concentration of B caused rate to x4

change in [A] -> x2

change in [B] -> x4

overall -> x8

hence doubling [B] quadruples rate

so order wrt B is 2nd order

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**BobbJo**)

yes

rate changes only due to change in concentration

both concentration of A and B changed

we know from 2 to 3 rate x8

from 2 to 3, [A] doubled. order wrt A is first order. so doubling [A] doubled rate

overall change in rate is x8

since we know change in [A] caused rate to double, other changes in rate must be due to [B]

so change in concentration of B caused rate to x4

change in [A] -> x2

change in [B] -> x4

overall -> x8

hence doubling [B] quadruples rate

so order wrt B is 2nd order

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#13

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can i use this same method for finding order of F in another question? once i found E is 2nd order, from exp 1 to 2, u x9 for rate, and to work out F using exp 2 and 3, E is also changing there, u x2 from exp2 to 3 so the effect on the rate in exp 2 would be 3.78x10-3 x4? and to work effect of F its 3.78x10-3 x2= 7.56x10-3. how does this mean F is 1st order? do i do 9/4= 2.25

**usernamenew**)can i use this same method for finding order of F in another question? once i found E is 2nd order, from exp 1 to 2, u x9 for rate, and to work out F using exp 2 and 3, E is also changing there, u x2 from exp2 to 3 so the effect on the rate in exp 2 would be 3.78x10-3 x4? and to work effect of F its 3.78x10-3 x2= 7.56x10-3. how does this mean F is 1st order? do i do 9/4= 2.25

from 2 to 3,

conc of E doubled, rate should x4

in fact, rate x 2

other changes in rate is due to change in conc of F

so change in conc of F caused rate to halve

[E] x 2 -> rate x 4 (2nd order)

[F] x 1/2 -> rate x 1/2

overall -> rate x 2

so halving [F] caused rate to 1/2

hence first order wrt F

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(Original post by

Yes method always works

from 2 to 3,

conc of E doubled, rate should x4

in fact, rate x 2

other changes in rate is due to change in conc of F

so change in conc of F caused rate to halve

[E] x 2 -> rate x 4 (2nd order)

[F] x 1/2 -> rate x 1/2

overall -> rate x 2

so halving [F] caused rate to 1/2

hence first order wrt F

**BobbJo**)Yes method always works

from 2 to 3,

conc of E doubled, rate should x4

in fact, rate x 2

other changes in rate is due to change in conc of F

so change in conc of F caused rate to halve

[E] x 2 -> rate x 4 (2nd order)

[F] x 1/2 -> rate x 1/2

overall -> rate x 2

so halving [F] caused rate to 1/2

hence first order wrt F

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