What is the rate equation and meaning of each symbol
Rate = k x [A]^a x[B]^b x[C]^c
k= rate constant
[A] = concentration of reactant A (mol dm-3) etc for B and C
a= order with respect to A. Etc for b and c (shows the number of particles involved in the rate determining step) (there is no link between balancing numbers and order numbers)
What does a 0 order reactant mean
The conc of that reaction had no effect on the rate of the reaction
What does a 1st order reactant mean
The rate of reaction is directly proportional to the concentration of the reactant
What does a second order reactant mean
The rate of the reaction increases exponentially with the conc of the reactant
What it’s important about the rate constant
It is only constant for a given reaction at a given temperature
How do you calculate the units of k
Units of rate / (units of concentration)^overall order
What is the overall order
The sum of all the individual orders
describe the zero order conc/time graph
straight line with a negative gradient
value of k’ is equal to the gradient
describe the first order conc/time graph
curve with a negative gradient
describe the second order conc/time graph
steeper curve then first with negative gradient
describe the zero order rate/conc graph
straight horizontal line
describe the first order rate/conc graph
straight diagonal line with positive gradient
describe the second order rate/conc graph
exponential curve
what is the isolation method
one of the reactants is isolated by putting the conc of all the others into vast excess so that any change in rate is due only to the conc of the reactant not in vast excess
how do you determine the order from the isolation method
use the conc/time graphs
if the order for a given reactant is first order that what is the rate of reaction directly proportional to
the concentration
what is special about a first order reaction conc/time graph
the half life is constant
how can you calculate the k’ from the first order conc/time graph
draw a tangent to the curve at a particular concentration and calculate its gradient(rate).
substitute into rate equation r=k’[A]^1.
OR k’=ln2/half life
for a second order what is the rate of reaction directly proportional to
the square of the concentration
what does the half life do in a second order conc/time graph
it is not constant, it has an increasing half life
experimental techniques that can be used for measuring the concentration of a reactant
colorimetry
measuring the volume of gas
measure a change in mass of the reaction
how does the initial rate method work
the initial rate at the start of the reaction is measured before the conc of any reactants has had the chance to change.
the conc of one of the reactants is then changed by a specific amount.
the ratio of the initial rates are then compared and the orders can be worked out
what equation do you need for the initial rate method and how do you select the experiments to use
(conc (exp a)/conc (exp b))^order= initial rate (exp a/initial rate (exp b)
find experiments where only one reactants conc changes
what do the order numbers say about the rate determining step
how many moles of each substance are in it
