Rates of Reaction Flashcards
Define rate of reaction
The change in concentration per unit time.
What units does rate of reaction have?
Mol¹Dm⁻³S⁻¹
What does the order of reaction indicate?
Reaction orders indicate how changing the concentration of a reactant affects the rate of reaction.
Describe how a zero order reactant would affect the rate of reaction
The concentration of the reactant has no effect on the rate of reaction.
Describe how the concentration of a first order reactant changes the rate of reaction
A first order reactant’s concentration is directly proportional to the rate of reaction.
Describe how the rate of reaction changes with the he concentration of a second order reactant
The rate of reaction is proportional to the square of the reactants concentration.
If a second order reactants concentration is tripled what whappens to the rate of reaction?
Increases by 9x
If a first order reactants concentration is doubled what happens to the rate of reaction?
The rate of reaction also doubles
What is the rate constant K?
The rate constant k is the proportionality constant, relating the concentration of reactants to the rate of reaction.
What does the overall order show and how is it calculated?
The overall order shows the overall affect of concentrations on the rate of reaction. It can be calculated by adding the reaction orders/ powers of the reactants. (m+n).
Define continuous monitoring
Continuous measurements taken over the course of a reaction.
For a concentration time graph what shape does zero order make?
Straight line with a constant negative gradient.
For a concentration time graph what shape does the first order make?
Downward curve with the gradient getting close to 0 as time increases.
How can concentration time graphs be plotted?
Using data from continuous monitoring.
How can the reaction rate be found using a concentration time graph?
Find the gradient of the concentration time graph.
Define half life
The time taken for half of the reactant to be used up.
What sort of half life do first order reactions have?
A constant half life (exponential decay)
How can the half life of a first order reactant be found on a concentration time graph?
Measure the time taken for the concentration to half.
How can a concentration time graph be shown as first order?
Each succesive half life should be the same.
What is the equation for calulating rate constant from half life?
K=ln2/t
t is half life
For a Rate-Concentration gaph what is the shape of a zero order reactant.
Straight horizontal line with no gradient.
For a Rate-Concentration gaph what is the shape of a first order reactant.
Straight line with a gradient starting at the origin.
How is the rate found from a first order reaction?
Find the gradient of the rate concentration graph.
What is the initial rate?
The instantaneous rate at the start of the reaction when t=0
How is a Rate concentration graph fromed from clock reactions (e.g. iodine clock)?
-Starting at a low concentration, the time taken for the brown/orange colour of aqeous iodine is measured.
-This is then repeated increasing the concentrations whilst still measuring the time.
-Once finished a table is made with concentrations and their times, with an additional column for 1/t.
-A graph is then modelled with 1/t (rate) against concentration using the concentration and 1/t values from the table.
Why can 1/t be used as rate, in a rate concentration graph?
1/t is proportional to rate.
Monitoring rate with a colorimeter is an exmaple of a “ “ method used to find reaction rates
Continuous monitoring
chemical clocks is an exmple of using “ “ to find reaction rates?
Initial rates
using chemical clocks to find out reaction rates is an “ “
the accuracy
approximate
Describe the process of measing reactions rates (producing a concentration time graph) by colorimetry
(e.g. Iodine)
1.A light source is set up aswell as a filter to control the wavelength of light passing through the solution, behind the filter is a colorimeter to measure the absorbance of light.
2.Place water between the filter and colorimeter and zero the colorimeter.
3.Measure the absorbance readings of a solution of varying concentrations (e.g. iodine) , producing an absorbance concentration graph.
4.Add a reactant (propanone) to a solution and then measure the absorbance at timed intervals.
5.Plot a concentration time graph using the absorbance time measurements from 4 but replacing abosrobance values with concentration values from 3.
What is the rate constant?
k
What is the rate determining step?
Slowest step of a multi step process, only includes reactants from the rate equation.
Why does increased temperature also increase the rate of reaction/rate constant.
-Increased temperature shifts the Boltzman distribution to the right, therefore more particles exceed or have the activation energy Eₐ needed to react.
-There is an increase in the amaount aof particle collsions as the particles move faster and collide more often.
In the Arrhenius equation what is the relationship between K and T
Exponential relationship between k and t
What must be done to the arrhenius equation before graphing to find Ea and A ( dont explain how to get A or Eₐ)
Ln both sides to get the equation Ln k = Eₐ/RT + Ln A
making a graph of ln K against 1/t.
How can A be found from a
ln K and 1/T graph
Find the y intercept to get ln A and then put the value of ln A to the e.
eˡⁿ ᵃ
How can Eₐ be found from a ln k against 1/t graph?
find the gradient to get -Eₐ/R
then multiple the gradient by -R, or -8.314
