3.5 Kinetics 2 Flashcards
What is meant by ‘rate of reaction’?
The change in conc of reactants or products over time
What is a rate equation?
for a reaction between A and B
rate = k[A]^m[B]^n
where m and n are integers representing the orders wrt each reactant, k is the rate constant
What is a rate constant?
The constant of proportionality linking the rate of reaction and the concentrations of the reactants raised to the power of the orders in the rate eqn
How do you calculate the units of a rate constant?
make k the subject sub units into eqn and cancel the common units
what is meant by the term ‘order of reaction’?
the order wrt a reactant is the power to which the concentration of the reactant is raised in the rate eqn
overall order of a reaction = the sum of all the individual orders of the reactants
what do the different orders of reaction mean?
0 order: if rate [A]^0 then the rate of reaction is unaffected by changing [A]
1st order: if rate [A]^1 then rate of reaction increases as the same rate as [A] increases
2nd order: if rate [A]^2 then rate will increase by the square factor of the factor [A] increases by
Activation energy
the minimum energy required for a particular reaction to occur
what are some of the different experimental techniques that allow you to obtain rate data?
titration
measuring the volume of gas released from a reaction over time
measuring the changes in mass of a reactant over time
measuring the time taken for a colour change
colorimetry
what are two different method types that can be used to investigate reaction rates?
Initial rate method: experiments are carried out where different initial concentrations of one reagent are used
continuous monitoring method: the concentration/ volume is continuously monitored so that a conc or vol time graph can be produced from data
how do you calculate the rate from a first order conc-time graph?
draw a tangent at the time you want to calculate the rate of reaction for
gradient of this tangent will equal rate of reaction
how do you calculate k from a first order rate-conc graph?
calc gradient of the line of best fit
gradient will equal the rate constant, k
how do you calculate the gradient of a line/ tangent?
gradient = change in y/ change in x
what is the rate determining step?
the slowest step of the reaction, only the species that take part in the rate determining step affect the rate
what is the relationship between the rate-determining step and the orders wrt the reactants?
the species present in the rate eqn are those that take part in the rate determining step
for any reactant in the rate eqn the order related to it tells you how many molecules of it are involved in the rate determining step
How does iodine react with propanone in acid?
CH3COCH3(aq) + I2(aq) -> CH3COCH2I(aq) + HI(aq)
solution turns from yellow to colourless, order wrt iodine is 0 and order wrt propanone and acid is first
rate = k[CH3COCH3][H+]
