1.9 Rate Equations Flashcards
What is the order?
It tells you how much the concentration of a reactant affects the rate
What is the individual order?
The power to which a concentration is raised in the rate equation
What is the overall order?
The sum of the individual orders in the rate equation
What is the rate equation?
rate = k[A][B]
With powers on the concentrations depending on the order
K=rate constant
What happens if a reactant is zero order?
It doesn’t appear in the rate equation
How do we work out an individual order?
Continuous monitoring
Initial rate method
What is continuous monitoring?
Graph - concentration v time
Then draw tangents of your curve and workout the gradients of each for the rate of reaction (Y/X)
Graph - rate of reaction v concentration
Draw lines from line of best fit to check (at least two)
How do you know what order it is?
First - the rate is proportional to the concentration
Second - the rate is proportional to the square of the concentration
Zero - the rate doesn’t depend on the concentration = no effect (defo the one in excess)
How to use the initial rate method? P1
From a data table you look at 2 experiments
Find one where the other reactant concentrations (B) are the same and (A) is different
Look at the difference of A’s between the experiments then look at the difference in the initial rate and work out the difference
Determine the order depending on if they both multiply by the same, the square or no effect
How to use the initial rate method? P2
Create a rate equation with the orders determined from the table
Then substitute and rearrange the rate equation to work out k (the rate constant)
What are the units for initial rate?
Mol dm^-3 s^-1
What is the rate determining step?
The slowest step in a chemical reaction
How do you work out the rate determining step?
You look at the rate equation and it is the step that has the same proportions of reactants
rate = k[A]^2[B]
RDS = (eg) B + 2A -> C
Be careful as some may be in disguise from previous steps
What do you workout in the Arrhenius equation?
Plot 1/T against ln k (log K)
(Might have to work out k from rearranging the rate equation with values?)
Workout gradient from plotted line y/x
Large (minus) number
Multiply this number by 8.31
Then divide by 1000 to put it in KJ mol-1
What should you remember when plotting 1/T in the arrhenius equation?
If you do the axis to x10^-3 make sure you multiply the number you use in the gradient calculation by x10^-3
