[Lilly]

Hi,

I have read a lot on 'rate constant' for chemistry rates of reaction but i still don't understand what it is . My chemistry A2 book does not explain it very well. In the book it explains 'calculations of the rate of decay of for-example cyclopropane, made at regular intervals (graph).'

and gives this table:

it says the third line in the table is constant and expressed as:
rate of reaction = k x [cyclopropane]
The proportionality constant is k, is called the rate constant.
Could you explain what is 'rate constant' in simple terms by relating to the data above and how it is linked to the 'order of reactions'?
Thank you
Sorry about the large images.

[Astrokel]

For simplicity, rate constant is a proportionality constant and is very important in study of kinetics. Order of reaction is determined through comparison of change in concentration with change in reaction rate and how is it linked to rate constant, is by the rate equation you have written.

[cliverlong]

Hello

I suggest you read this for a starter

http://www.chemguide.co.uk/physical/basicrates/orders.html#top

There is a subtle step in the information you have been given that hasn't been emphasised but is crucial to the analysis

If you are taking a graphical analysis, first you plot concentration against time (see your graph) and measure the gradient (see the table) to give you rate. Rate is always taken to be a positive value even if gradient is negative.

Second you plot rate against concentration - that is the third row in the table you have scanned. Only in the case the gradient of this second curve (which you haven't been given but the value is 6.7 x 10-4) is constant can you say that order is 1 for that reactant.

Rates take some time to understand but the example you are given isn't explained in a detailed enough way for this to make sense.

Clive