reaction kinetics Flashcards
What is meant by rate of reaction?
The change in concentration of reactants
or products over time.
How does concentration affect rate of reaction?
● Increasing the concentration increases the
number of molecules per unit volume.
● This leads to more frequent collisions and
hence a greater frequency of successful
collisions.
● This increases the rate of reaction.
What is activation energy?
The minimum amount of energy required
for a particular reaction to occur.
What is the Boltzmann distribution?
● The Boltzmann distribution
shows the relative energies of
molecules.
● Area under the graph = total number of molecules.
● As you can see, only a small proportion of molecules have energies greater than the
activation energy.
Using the Boltzmann distribution to explain the effect of
temperature on the rate of reaction
● Increasing the temperature increases the kinetic energies of the molecules.
● This means a greater proportion of molecules have energy greater than the activation energy.
● Hence rate of reaction increases as more molecules are able to react.
● You can also see from the diagram that the average energy of the molecules is also greater.
How does the rate constant, k vary with increasing
temperature? (A level only)
● As temperature increases there are more particles with energy
above the activation energy. As a result, there are more
frequent successful collisions so rate of reaction increases.
● An increase in temperature therefore causes an increase in k.
● For every 10℃ increase, the rate and k both approximately
double.
What is catalysis?
The increase in rate of a chemical
reaction due to the addition of a catalyst.
What is a homogeneous catalyst?
A catalyst that is in the same state as the
reactants.
What is a heterogeneous catalyst?
A catalyst that is in a different state to the
reactants.
Why do catalysts increase the rate of reaction?
they provide an alternative reaction pathway with a lower activation energy which means that more particles will have sufficient energy to overcome the energy barrier and react. They remained unchanged after the reaction
What are enzymes?
● Biological catalysts that increase the
rate of biochemical reactions.
● Proteins with a specific structure.
● Typically catalyse a specific reaction.
what is the effect of increasing surface area on a reaction
- increasing surface area increases chances of a collision as more particles are exposed
- powdered solids react quicker than larger lumps
- the greater the surface area, the faster the rate of reaction
what is the effect of increasing concentration in a reaction
more frequent collisions which leads to an increased rate of reaction. increasing the concentration for some reactants can have a greater effect than increasing others
what is an autocatalyst
a product that acts as a catalyst in its reaction
how does the rate of an autocatalysed reaction change
they are slow at first and become more rapid as the catalyst is produced
