A6 kinetics 2 Flashcards
Define Rate of Reaction
Change in quantities of reactants or products over time
What does it mean if the reaction is 0th order with respect to a reactant
Changing the concentration will have no effect on rate
What does it mean if the reaction is 1st order with respect to a reactant
Concentration is proportional to rate
What does it mean if the reaction is 2nd order with respect to a reactant
Concentration is proportional to rate (^2)
When given a table to determine the reaction order with respect to a reactant, what must always be included in the explanation of each reactant
From experiment X to Y
How the concentration of each reactant changes
How the rate changes
The reaction will be 0th/1st/2nd order with respect to the reactant
What will always be included in the rate equation
Rate = k [reagents that are 1st or 2nd order]
How are 0th order reactants included in rate equations
They are not
How are 1st order reactants included in rate equations
To the power of 1 (by itself)
How are 2nd order reactants included in rate equations
Squared
Define Overall Order
Overall effect of the concentrations of all reactants on the rate of reaction
How to determine the overall order of a reaction
The sum of the orders of the reactants
How can the rate constant, K, be determined from a rate equation
Re-arrange so that K = rate / [reactants]
What will the unit for rate always be
dm -3 mol s-1
What will the unit for K always contain
s-1
How should answers in kinetics always be written
dm then mol then s
What does the red line represent on this concentration-time graph
A reactant that is first order
What does the blue line represent on this concentration-time graph
A reactant that is 0th order
Describe the line on a concentration-time graph, that is 1st order
Line where consecutive half-lives are constant
Describe the line on a concentration-time graph, that is 0th order
Straight line, with a constant negative gradient
Define half-lives
time taken for half of a reactant to be used up
t1/2
On a concentration-time graph, what does it mean if a reactant has constant consecutive half-lives
The reaction is 1st order with respect to the reactant
When can the value of K be determined from a concentration-time graph
When the reaction is first order with respect to the reactant
What is the formula for K when calculating with a 1st order concentration-time graph
What is an alternative to using the following formula to determine K on a 1st order concentration time graph
Drawing a tangent to the line at t=0s, and determining the gradient
What does the blue line represent on this rate-concentration graph
A 0th order reactant
What does the red line represent on this rate-concentration graph
A 1st order reactant
What does the green line represent on this rate-concentration graph
A 2nd order reactant
Describe a 1st order reactant on a rate-concentration graph
Line that goes through the origin, with a constant positive gradient
Describe a 0th order reactant on a rate-concentration graph
A horizontal line, with a gradient of 0
Describe a 2nd order reactant on a rate-concentration graph
A curve that has a gradient that gets more positive, as concentration increases
When investigating initial rate, what should be ensured when the reaction is 0th order to a reactant
A large excess of it is used, to ensure that the concentration is constant throughout
What must be ensured when investigating initial rate with reactants that are 0th order
A large excess of it is used, to ensure that the concentration is constant throughout
Why is a large excess of a 0th order reactant used when determining initial rate experimentally
To ensure that the concentration is constant throughout
When is colorimetry used experimentally in initial rates reactions
When one of the reactants is coloured (E.g iodine solution is orange)
What is the trend with absorbancy (measured with a colorimeter) when a reactant is coloured
Absorbancy decreases as concentration decreases
Define rate-determining step
The slowest step of the reaction
Of all the reactants in an equation, what reactants will the rate equation include
Only those from the rate-determining step
How to tell that a mechanism is consistent with the rate equation
When all the mechanism steps (before and including the rate determining step) together give the reactants and products in the same stoichiometric ratio as in the rate equation
When all the mechanism steps (before and including the rate determining step) together give the reactants and products in the same stoichiometric ratio as in the rate equation
The mechanism is consistent with the rate equation
Why would a two-step mechanism be unlikely to occur in one step
Stoichiometry in the rate equation doesn’t match stoichiometry in overall equation
Successful collisions are unlikely with more than two particles
For Arrhenius graph, how is the Ea determined
Draw a Maxwell-Boltzmann graph, and show and explain how an increased temperature would affect this
Increasing temperature means that there is a greater area under the curve above the activation energy
A greater number of molecules have energy greater than the activation energy
Equation for determining activation energy from an Arrhenius graph
Units for gradient on Arrhenius graph
K
What does the y-intercept of an Arrhenius graph represent
ln A
How to determine A from an Arrhenius graph
e (to the power of intercept number)
Equation for ln K of Arrhenius graph
How to determine ln K from an Arrhenius graph
Units for horizontal line of Arrhenius graph
K (-1)
rate equation
rate = k (square brackets) ^ order ()^
if ()^ 0 –> if it is to the power of zero remove from equation
rate and order Link
n ^x = change in rate
n = change in conc
what does half life do
determines 1 order
- constant change
rate constant from half life
k = ln 2 / t 1/2
graph
calculate Ea
plot graph ln k aginst 1/T
gradient = -EA/ R
find A from Ln k against 1/T graph
find y intercept
A= e ^ y intercept
Ln A = y intercept
initial rate
t= o
draw tangent at t=0
on conc - time graph
calculating rate from conc time graph
constant half life at value
means first order
initial conc t=o
rate equation
tangent at 1st half life
e.g. 1 –> draw tangent at 0.5
Arrehenius equation labeled
log Arrhenius equation
what is the initial rate of reaction for a conc time graph
gradient of tangent drawn on the line
techniques used to investigate rate of reaction
measure change in vol of gas
measure change in mass
colorimetry
does pressure or conc effect boltzmsn
no - not changing the energy of particles
k from conc time graph
tangent drawn
gradient of tangent - rate of reaction
rate = gradient
k = rate / conc
sub in vaules
rate constant from rate conc graph
determine orders (shapes)
rate = k ()
gradient = rate constant
gradient = change in rate/ chang in conc
The catalyst is solid while the reactants are gases
so the catalsyst is a different state from the reactants therefore heterogenous
The use of catalysts in industrial processes can be beneficial to the environment. state one reason for this
1- catalyst Lower the energy demand for a reaction
2- less combustion of fossil fuels and therefore lower carbon dioxide emissions
3- Allows different reactions to take place with greater atom economy/ less waste
4- allows less toxic chemical to be used
Suggest how the conc of bromine could have been monitored
measure reduction of colour of bromine
suggest a different experimental method that would allow the rate of this reaction to be followed over time
measure vol of co2 produced
why would use of excess HCOOH ensure that the order with respect to HCOOH is effectively zero
conc of HCOOH would be constant
