Topic 9 - Kinetics I Flashcards
What is the Collision Theory
a reaction won’t take place unless
1. two particles are correctly orientated
2. two particles collide with a certain minimum amount of kinetic energy
What is activation energy
the minimum amount of energy particles need to react
What are the axes of a Maxwell-Boltzmann Distribution curve
y = n.o of molecules
x = energy
What does a Maxwell-Boltzmann Distribution curve look like
- starts at (0,0) because no molecules have zero energy
- peak = most probable energy
- mean energy = to the right of peak
- shaded area on right = molecules that have at least activation energy
What affect does increasing temp have on Maxwell-Boltzmann Distribution curve
more particles on average have at least activation energy
- entire curve shifts right
- area stays same as total n.o molecules is same
Why does increasing temp speed up rate of reaction
particles moving faster = more likely to collide more often
What affect does using a catalyst have on Maxwell-Boltzmann Distribution curve
activation energy is lower
more particles have at least Ea.
How does increasing concentration speed up rate of reaction
more particles in a given volume = collide more frequently = more chance
How does increasing pressure speed up rate of reaction
gases only = more particles in given volume = higher frequency of successful collisions
How does a catalyst speed up the rate of reaction
provides an alternative reaction pathway with a lower activation energy
What is reaction rate
change in amount of reactant or product per unit time
What is a heterogeneous catalyst
in a different phase from reactants
How does heterogeneous catalysis work
- reactants diffuse onto the surface of catalyst
- adsorption takes place = bonds for between catalyst & reactants, strong enough to break covalent bonds in reactants, weak enough to eventually break
- reaction takes places on surface of catalyst
- desorption takes place = bonds with catalyst have weakened/broken, product diffuses away from catalyst
What does the reaction profile with a homogeneous catalyst look like ?
height of curve with activation energy is lower (one peak)
What is homogeneous catalyst
in same phase as reactants
How does homogeneous catalysis work
reactants combine with aqueous catalyst to make an intermediate species, which then reacts to form products and reform catalyst
What does the reaction profile look like for homogeneous catalysis
- one high peal becomes 2 smaller ones
- intermediate where dips between 2 small peaks
