A2 Kinetics

A guide to all the kinetics stuff with the exception of the rate determing step. Enjoy.

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Rate, kinetics and orders
What you SHOULD be able to do by the end of the section:
Define the terms: Rate of reaction, Rate constant (k), order of a reaction and the overall
order of a reaction.
Work out the order of a reaction bases on initial rate data.
Calculate K and its units from initial rate data.
Predict a change in K based on a change in conditions.
Important definitions:
Order: A number used to describe how a reaction rate is affected by the concentrations of a
certain product in a reaction.
Overall Order: The total of all the orders of all products added together. Example if A+B C
and A had an order of 3 and B had an order of 5 then the overall order would be 8 (5+3).
Rate of reaction: A term used to describe the change of the concentration of products
made over a set period of time.
Rate Constant: A number in a rate equation often known as K that is only changed when
temperature or pressure increases.
How to determine a reaction order
When it comes to determining order, you'll mainly have to worry about deducing your order based
on previous data, there are 2 ways of data presentation, you have to worry about:
1. Tabular (data is in a table)
2. Graphically (data is in a graph).
We'll firstly start with a tabular question as they like to be nice a frequent (bless them).
Let's say that we added chemical A and chemical C together to make chemical B. Our teacher then
decided to make use deduce the order of A and C in the experiments. So what do we do?
Experiment Concentration of A Concentration of C Initial Rate
1 1 x 10-3 1 x 10-3 1 x 10-3
2 1 x 10-3 0.5 x 10-3 0.25 x 10-3
3 4 x 10-3 2 x 10-3 16 x 10-3
Well at first glance this table might be horrible, icky and full of numbers however it is possible to
deduce the order of both A and C and thus deduce an overall order.

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Page 2

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Let's tackle C first. If we look at the table again, we notice that the experiment 1 and 2 both have the
same concentration of A. So we'll concentrate on solely those 2 experiments for the time being
(otherwise we'll get confused), to make it clearer we'll highlight them in pink.
Experiment Concentration of A Concentration of C Initial Rate
1 1 x 10-3 1 x 10-3 1 x 10-3
2 1 x 10-3 0.5 x 10-3 0.…read more

Page 3

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However this requires some rearranging:
K= rate/ [A]1 x [C]2
So in experiment one's case:
K= 1 x 10-3 / [1 x 10-3] x [1 x 10-3]2
K= [1 x 10-3]2 (because of cancelling).…read more