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Topic: Rate Laws and order of reaction  (Read 283 times)

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Offline Jackmcnulty

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Rate Laws and order of reaction
« on: November 11, 2021, 04:04:13 PM »
Consider: A + 2B  :rarrow: C + 2D

It is asking me what the order of reaction with respect to B and A are. I understand the rate law that states

Rate = k[A]mBn

However I do not understand where the values for m and n are coming from.

We were also given tabulated data about [A]0, and B0 and Initial Δ[C]/Δt.

Is there something about this tabulated data that should tell me? Where B is not in brackets, the formatting messed it up and it is in fact the molarity of the reactant B.

Offline Orcio_Dojek

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Re: Rate Laws and order of reaction
« Reply #1 on: November 11, 2021, 04:18:29 PM »
Quote
Rate = k[A]mBn

However I do not understand where the values for m and n are coming from.
Values "m" and "n" need to be calculated. If you have the data about concentration of A and B I suggest to draw a graph - concentration of A, B, C and D versus time of the reaction.

Offline Borek

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Re: Rate Laws and order of reaction
« Reply #2 on: November 11, 2021, 05:41:31 PM »
However I do not understand where the values for m and n are coming from.

Technically they reflect stoichiometry of the reaction as it happens - which sometimes, in the case of very simple reactions, is eactly what the reaction equation says, but in most cases they reflect so called elementary reactions - which are simpler steps towards the full, complete process, described by the balanced equation.

From the data you have you shoudl be probably able to determine m and n. It is often not trivial to do so, see Rate equation page in wikipedia.
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Offline mjc123

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Re: Rate Laws and order of reaction
« Reply #3 on: November 11, 2021, 05:43:25 PM »
B in brackets is the format code for bold type. For concentration of B, you can just include a space, e.g. [B ].

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