Kinetics 1 Flashcards
Collision theory
For 2 reactant particles to react:
Particles must collide at the right orientation
Collisions must have sufficient energy ‘Ea’
Activation energy
For a reaction to start an energy threshold needs to be met
Energy profile diagram
A diagram which shows the enthalpy over progress of reaction
As well as an arrow representing the activation energy
Bonds broken over an energy profile diagram
Bonds begin to stretch as energy increases
At the top (at activation energy) the bonds are broken because they overcame energy barrier to react
What is the rate of reaction
The rate at which reactants are converted to products
Or products are formed from reactants
What can rate of reaction be measured by?
The rate at which reactants are used up
The rate at which products are formed from
How to calculate rate of reaction?
Change in concentration of product formed/reactant used up
——————————————
Change in time
Unit of rate of reaction
g s⁻¹
mol s⁻¹
Factors affecting the rate?
Temperature
Surface area
Catalysts
Concentration of reactants
Pressure of gas reactants
A maxwell-Boltzmann distribution
Plotting a graph to show the distribution of energy across the number of particles involved in a reaction
What does a Maxwell-Boltzmann distribution look like?
Number of molecules = y axis
Ek of molecules = x axis
Distorted bell curve shifted to the left which starts at 0 but never reaches 0 on other end
Eaon the right end
Why do Maxwell-Boltzmann distributions always start at 0,0?
Because no particles will have 0 energy, so shows absence of particles
Where on a Maxwell-Boltzmann graph show the number of particles which react?
The area under the bit of the graph passing the activation energy showing they have collided with successful energy (over the Ea)
Does the Maxwell-Boltzmann graph ever hit 0 on the other side?
No, only runs parallel to x axis because all particles must have some level of energy
What does the area under a Maxwell-Boltzmann graph show?
The total number of particles
How does increasing concentration affect rate of reaction?
More particles are in a given volume thus are more are able to react
So more collisions occur
So more successful collisions which overcome Ea occur
=increases rate of reaction
How can we measure the affect of surface area on rate of reaction?
Using marble chips of different sizes by measuring volume of CO2 gas collected when reacted with HCl
Effect of concentration on maxwell-Boltzmann distribution?
Increases along the y axis but no move in the curve along x axis
Because there is a higher number of particles in a given volume thus more particles collide with sufficient energy
How does increasing temperature affect the rate of reaction?
Particles have more kinetic energy so collide more
Therefore greater proportion of molecules collide with sufficient energy to surpass Ea
Effect of temperature on a maxwell-Boltzmann distribution?
Graph is moved to the right showing that higher number of particles have more energy and also more particles surpass Ea
But because there is still same no. Of particles, the area must be the same so offset this by the peak being lower at higher temps
What is the effect of pressure on rate of reaction?
There are more gaseous molecules per unit volume by increasing pressure
So this increases frequency of collisions between reactant molecules
Thus more collisions overcome the activation energy and can react
Effect of pressure on maxwell-Boltzmann distribution
