3.2.2 Reaction Rates Flashcards
What’s the collision theory
For reactions to occur, particles must collide with each other with enough energy to break the bonds in the reactants
Why are only a small % of collisions successful
As there’s an energy barrier to breaking bonds
What do particles need to over come the barrier and react on collision
Enough energy (activation energy , Ea)
What are activation energies like for different reactions
Different
Define activation energy, Ea
Minimum amount of energy needed for a reaction to occur
What type of reaction has the most activation energy
Endothermic
What is the rate of reaction
+ equation
Change in concentration per unit time
Rate of reaction = amount of product produced/time taken
How could u work out the total number from a distribution curve
The area under the curve
What does the Maxwell-Boltzmann energy distribution curve show
The distribution of energies of particles in a gas
On Maxwell-Boltzmann energy distribution curve how many particles are at zero energy
0
On the Maxwell-Boltzmann energy distribution curve where does the curve never actually reach
Why
The x axis
As there will always be particles of very high energy
On the Maxwell-Boltzmann energy distribution curve what’s the area under the curve equal to
The total number of particles
What does the peak on a Maxwell-Boltzmann energy distribution curve indicate
The most probable energy (modal value/most common)
On Maxwell-Boltzmann energy distribution curve where’s the activation energy
What does this show you
The shaded bit to the left
Shows the amount of particles that can only react on collision
If temperature is increased what happens to the Maxwell-Boltzmann curve
Peak shifts to the right (higher energy)
Lower in height
Broader
On the M-B curve if temperature is increased, what are the particles like
So What’s the area under the curve like
Will be a general increase in number of particles at higher energies , but total number of particles is the same
Area under curve stays the same
On the M-B curve with a temperature change , what’s the rate like
There’s a large increase in rate as there’s now many more particles (double) that possess an energy greater than activation energy
What happens to the M-B curve if temperature is decreased
Curve moves left + peak is higher
What are the particles on the M-B curve like when temperature is decreased
What happens to rate
1/2 number of particles possess activation energy
So rate of reaction decreases
What does a catalyst do to activation energy
Lowers it
What does the M-B curve look like when a catalyst is used
The same - no shape change + no change in energy of particles
What happens to rate when a catalyst is added
Rate increases
As there are now more particles that have greater energy than activation energy
What 4 factors affect rate of reaction
Temperature
Catalyst
Concentration
Pressure
If temperature is increased, what happens to rate
Particle speed increases + more collisions occur
More kinetic energy
Rate of reaction is quicker -> amount of product produced is the same but it’s just produced quicker
What does a catalyst do
Speeds up rate of reaction but is chemically unchanged at the end
How does a catalyst work
Increases rate by providing an alternative reaction route of lower activation energy
What happens to rate with higher concentration
Increases as there are more particles present in a given volume so there are more collisions
What does increasing the pressure of a gaseous reaction do to rate
Increases rate as the particles are now forced closer together so collide more frequently
When may pressure not increase the rate + product yield
If a gas reaction is in equilibrium (le chatelier’s principle)
What are the 2 types of catalyst
Homogenous
Heterogenous
What are homogenous catalysts
In the Same physical state as reactants e.g all liquids
What are heterogenous catalysts like
E.g of process
In a different physical state to reactants
E.g haber process (solid catalyst, gaseous reactants)
Why are catalysts important for the economy + sustainability
90% chemical materials made with catalysts
They lower Ea which reduces temperature required for reaction, so less fuel (fossil fuels) are needed reducing costs
Less CO2 (g) released into environment
