A-level Chemistry Rate Practical Question

Hi, how would you use information from a concentration time graph drawn with data from a continuous monitoring reaction, to find the order with respect to the reactant and the rate constant? Thanks.

Reply 1

_Simo_

Hey there!

If you have all the initial concentration of all the reactants, you can use the initial rate method and find the initial rate of the reaction on the graph (t=0). Do you know how?

If you have only the graphs of time against concentration the order of the reaction wrt a reactant can be extrapolated from the shape of the graph hence the proportionality of time and concentration.
direct proportionality= zeroth order
exponential with t1/2 constant = first order
exponential with t1/2 non constant = second order

if the graphs are of concentration against rate or in logarithmic scale the graph is a bit different.

Regarding the K of the reaction rate, once you have found the order of the reaction wrt each reactant and the reaction rate equation is a matter of rearranging the equation and find the constant using the data collected (initial rate and initial concentrations of the reactant of the rate determining step)

Let me know how you get on and if you need any more help with anything.

cheers :cool:

Original post by Har6547

Hi, how would you use information from a concentration time graph drawn with data from a continuous monitoring reaction, to find the order with respect to the reactant and the rate constant? Thanks.

Reply 2

Illumilottie

Original post by Har6547

Hi, how would you use information from a concentration time graph drawn with data from a continuous monitoring reaction, to find the order with respect to the reactant and the rate constant? Thanks.

To find the order with respect to the reactant have a look at the shape of the graph
It if it’s a straight line with a negative gradient it’s 0 order
If it’s a curved line with a negative gradient and a constant half life it’s 1st order
If it’s a steep curved line with a negative gradient it’s 2nd order

To find the rate constant K you should draw a tangent at a point on the graph and calculate the rate of the reaction from the gradient
At this point apply the formula K = rate / concentration of the reactant at the point in which you have taken the tangent.

Or if your reaction is first order you can do ln2 / half life

I’m not a pro at chemistry but I think this is correct. Hope it helps