Topic 16 - Kinetics 2 Flashcards
What a the rate of reaction?
the change in the amount of reactants/products per unit time
What is a rate equation?
an equation that shows the relationship between the concentrations of reactants and the rate of reaction
eg. rate = k[A][B]
What is an order?
a power in the rate equation that tells us how any change in concentration of a reactant affects the rate
What is zero order in respect to a reactant?
when the concentration of the reactant has no effect on rate
eg. [X] doubles, rate stays the same
What is first order in respect to a reactant?
when the change in magnitude of the concentration of a reactant has the same impact on the rate
eg. [X] doubles, rate doubles
What is second order in respect to a reactant?
when the change in magnitude of the concentration of a reactant has the squared effect on the magnitude of the reactant concentration on the rate of reaction
eg. [X] doubles, rate quadruples (as 2²=4)
What is the overall order of a reaction?
the sum of all the orders within the rate equation
What method can be used to obtain a rate of reaction when there is a change in volume?
by inversion or with a gas syringe
-measure the volume of gas produced
What method can be used to obtain a rate of reaction when there is a change in mass?
place conical flask where the reaction is occurring on a high resolution balance and measure the change in mass
(when a gas is being produced, mass decreases but when a gas is being used as a reactant, mass increases)
What method can be used to obtain a rate of reaction when there is a change in colour?
disappearing cross experiment (when there is a change from colourless to coloured or vice versa) -measure the time taken for cross to disappear/appear
colourimetry (measure percentage transmission/absorbance at fixed time intervals and plot a graph of time against transmission/absorbance or use a calibration curve to determine concentrations)
What method can be used to obtain a rate of reaction when there is a change in the conductivity of the reaction mixture?
condumetric analysis
usually used for inorganic reactions as conductivity depends on the number and types of ions present (ie. size and charge of ions)
What method can be used to obtain a change in concentration of a particular substance at a particular time?
titration
remove aliquots at different time intervals and quench so that titrations can be done of all the different times
What is colorimetry?
a method which uses percentage transmission/absorption of light during a reaction which involves a change in colour to determine the concentration of a reagent
What shape is a graph of concentration against time when the reactant is at zero order?
straight line (going down) -constant gradient
What shape is a graph of concentration against time when the reactant is at first order?
downwards curve
- gradient gets less and less steep
- half lives are constant
What shape is a graph of concentration against time when the reactant is at second order?
downwards curve
- gradient gets less and less steep but is steeper than first order
- half lives increase
What shape is a graph of rate against concentration when the reactant is at zero order?
horizontal line
What shape is a graph of rate against concentration when the reactant is at first order?
straight line (going up) -constant gradient
What shape is a graph of rate against concentration when the reactant is at second order?
upwards curve
What are tangents drawn at t=0 equal to?
initial rate
What is the rate determining step of a reaction?
the slowest step which determines the rate of reaction
-only species in the RDS will appear in the rate equation
What order are solid catalysts always at?
zero order
∴ they never appear in the rate equation
Why is the rate determining step equivalent to the overall rate of reaction?
RDS is always the slowest so rate can only go as quick as this step
What is the Arrhenius equation?
k=Ae^(-Ea/RT)
rearranged: lnk = lnA -Ea/RT
What conditions affect the rate constant?
only temperature (higher temp = higher rate)
How is the Arrhenius equation in the format of y=mx+c?
lnk = lnA -Ea/RT is like y=mx+c when: y = lnk m = -Ea/R x = 1/T c = lnA
How can activation energy be found from a gradient of a graph of lnk against 1/T?
Ea = gradient × -R
R = -8.14
What is the overall order of a hydrolysis of a primary halogenoalkane?
second order
What is the overall order of a hydrolysis of a tertiary halogenoalkane?
first order
What is the mechanism of the hydrolysis of a primary halogenoalkane? And how does the rate equation act as evidence for this?
SN2 mechanism
-2 species in RDS/rate equation
What is the mechanism of the hydrolysis of a tertiary halogenoalkane? And how does the rate equation act as evidence for this?
SN1 mechanism
-only 1 species in RDS/rate equation
In the iodine clock reaction, why should the total volume be kept the same?
so that volume of ions is proportional to concentration
