collision theory
particles must collide with enough energy and be in the correct orientation for them to react
factors affecting the rate of reaction
temperature
concentration
SA:V
pressure
catalyst
How do you know if a substance acts as a catalyst in a reaction?
A- + H+ — T+ + C
T+ + B- — D + H+
overall: A + B — C + D
H+ is reformed so it acts as a catalyst
activation energy
minimum amount of energy needed for reactants to react
what is catalysis?
Types:
a reaction that uses a catalyst to start it
homogenous catalyst
heterogenous catalyst
homogenous catalysts
same phase as reactants
usually in solution
heterogenous catalysts
- where it is used
- issues
different phase from reactants
usually solid catalyst and gaseous reactants
occurs on surface of catalysts
E.Gs: haber process, contact process
issues: poisoning (catalysts can get ruined) or active sites can get blocked by sulfur
Maxwell - Boltzmann distribution curves:
- what state are particles in?
- energy of particles
shows distribution of particles at a set temperature
refers to gas particles only
no particles have 0 energy (all have some KE); only particles with energy >= Ea will react so very few react
Maxwell - Boltzmann distribution curves:
- where to find mean energy, probable energy (Emp)
- how to find number of particles
- x and y axes
probable: peak of curve
mean: slightly to the right of probable energy
area under curve: no. of particles
x: energy
y: number of particles with energy (only touches axes at origin)
which factor can change the distribution of the Maxwell - Boltzmann curve?
temperature
As temperature increases, what happens to the Maxwell - Boltzmann distribution curve?
shifts to the right and peak is lower
more particles have energy greater than Ea
if lower temp, graph shifts to left and peak is taller
As concentration increases, what happens to the Maxwell - Boltzmann distribution curve?
graph has a higher peak with the same x value (moves up)
more particles with energy greater than Ea
What happens to the Maxwell - Boltzmann distribution curve when a catalyst is used?
graph stays the same but the Ea line shifts to the left because more particles have an energy greater than Ea
As pressure increases, what happens to the Maxwell - Boltzmann distribution curve?
everything stays the same as there are the same number of molecules and particles have the same KE
How increasing the temperature changes the rate of reaction:
increasing the temperature means that many more particles have an energy greater than or equal to the activation energy so more reacting particles can overcome the energy barrier and form products
Are more frequent, successful collisions
RP 3 disappearing cross:
- If a bigger conical flask was used, how does this affect the time taken for the cross to disappear?
increases it
RP 3 disappearing cross:
- How does rinsing the flask with acid decrease the accuracy of the experiment?
Means there is acid on the walls of the flask which has not been accounted for during measuring, so you get a faster - than expected reaction
how increasing the concentration affects the rate of reaction:
many more molecules in a given area so there are more frequent, successful collisions
