IB Chemistry



TEMPERATURE is the only thing that changes the rate

Rate of rection depends on how quickly the concentration of the product or reactant changes with respect to time

Rate of reaction = increase in product concentration/ time taken

change in product/ change in time

UNIT of rate: concentration/ time

Species react as a result of collisions of sufficient energy and proper orientation

Concentration changes in a reaction can be followed indirectly by monitoring changes in mass, volume and colour.

Activation energy (Ea) is the minimum energy that colliding molecules need in order to have successful collisions leading to a reaction.

By decreasing Ea, a catalyst increases the rate of a chemical reaction, without itself being permanently chemically changed.

SLOW STEP= RDS because it prevents the other processes from reaching the end of the reaction and in this way determines the overall rate

If a graph of rate against time is plotted then the shape obtained will depend on the overall order of the reaction.

  • 0th order graph:- straight flat line 
  • 1st order graph:- straight line 
  • All other orders: curve 

If a curve is obtained then further mathematical treatment of the results is necessary.

as: Rate = k[A]m[B]n

if [B] is kept constant, then: log Rate = log k' + m log[A] 

And a plot of log Rate against log [A] will give a straight line of gradient m (the graph has the form y = mx + c)

keeping [A] constant and treating the results of rate when [B] varies will allow a similar determination of the order with respect to B. Once the two orders are ascertained then the rate constant k can be found.

Then to find k you put the numbers from 1 reaction into the rate expression.


- is involved in the RDS     -introduces a step


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