F. Kinetics Flashcards
What is collision theory
Reactions can only occur when collisions take place between particles with sufficient energy (activation energy)
Name all the factors that affect the rate of reaction
- temperature
- concentration of a solution
- pressure of a gas reaction
- surface area of solid reactants
- using a catalyst
What is activation energy
The minimum energy that a particle needs in order to react or the enthalpy change between the reactants and the transition state
What is the transition state
The species that exists at the top of the curve of an enthalpy diagram
What does the Maxwell-Boltzmann distribution show
The distribution of energy amongst the particles. It shows:
- no particles have zero energy
- most particles have intermediate energies
- a few have very high energies (there is no upper limit)
Why does the Maxwell-Boltzmann distribution go through the origin
All particles have energy/ no particles have no energy
Why does the Maxwell-Boltzmann distribution never touch the x-axis after it goes through the origin
There is always a probability that a particle has any energy even a very high one
Describe the effect of temperature on a Maxwell-Boltzmann curve
- curve shifts to the right
- number of particles with very high energy increases
- total area under the curve remains the same
- number of particles with Ea increases
What are catalysts
A catalyst is a substance that increases the rate of a chemical reaction without being changed in chemical composition or amount
How do catalysts work
They provide a different reaction pathway with a lower activation energy
Describe the effect of a catalyst on a Maxwell-Boltzmann curve
It moves the position of the Ea down the x-axis on the graph
Describe a catalytic converter
a honeycomb, made of a ceramic material, coated with platinum and rhodium metals (the catalysts). honeycomb to increase surface area.
Describe 2 catalytic converters reactions
carbon monoxide +nitrogen oxides——> nitrogen and carbon dioxide
hydrocarbons + nitrogen oxides——> nitrogen +carbon dioxide + water
Describe the steps of the reaction that take place on the catalytic converter
- adsorption - gases form weak bonds with metals atoms of the catalyst. The gases react on the surface.
- desorption- the products break away from the metal atoms.
What is the rate of a reaction
The change in concentration per unit time
What is the rate expression for A + B —-> C
rate= [A]^m[B]^n
m and n are the orders of the reaction
What is the overall order for the reaction for a reaction with the rate equation rate= [A]^m[B]^n
m + n
What is the unit for the rate constant for a 0 order reaction
rate = k
moldm^-3 s^-1
What is the unit for the rate constant for a 1 order reaction
rate = [A]
s^-1
What is the unit for the rate constant for a 2 order reaction
rate = k[B][C]
mol^-1 dm^3 s^-1
What is the unit for the rate constant for a 3 order reaction
rate = [D][E]^2
mol^-2 dm^6 s^-1
What does a graph of rate v [A] look like is As order is 0
Horizontal line as the concentration of A doesn’t effect the rate
What does a graph of rate v [A] look like is As order is 1
Directly proportional line as rate=[A]^1
What does a graph of rate v [A] look like is As order is 2
Exponential line as rate=[A]^2
What is the initial rate method
- a series of experiments each with different starting concentrations
- concentration vs time graph plotted
- tangent is drawn at t=0
- by drawing initial rate the conc. of all substances in the reaction mixture are known
What does the effect of an increase of temperature have on k
Increases
What does e^(-Ea/RT) show
The fraction of molecules with energy greater than the activation energy
- Ea is activation energy in Jmol-1
- R is gas constant
- T is temperature in K
What is the Arrhenius equation
k=Ae^(-Ea/RT)
k-rate constant
A-pre-exponential factor
e^(-Ea/RT)-The fraction of molecules with energy greater than the activation energy
What is the rate determining step
The slowest step in the reaction mechanism. It governs the rate of the overall reaction
A+B+C ---> Y + Z 1. A + B ---> (fast) D 2. D ---> (slow) E 3. E + C ---> Y + Z (fast) What is the rate equation for this reaction
rate=[A][B][D]
2 is rate determining step but the rate of step 1 might effect the overall rate
What is the iodine clock used to measure
The rate of reaction between hydrogen peroxide and potassium iodide
How is the iodine clock measured
Adding a known number of sodium thiosulfate and starch which gives an end point when solution goes dark blue/black
