Reaction Rate Flashcards
Define Reaction Rate:
Defined as the change in concentration of reactant/product over a period of time.
Reaction rate = Amount of substance used/produced over time.
Collision Theory
- Reactants must collide with each other.
2.Must collide with each other with enough energy to break the bonds within the reactants.
3.Collide with correct orientation to break the bonds and to form new bonds.
All of these must occur for a reaction to occur.
Activation energy
It is the minimum amount of energy required to get a reaction going.
If the energy is equal or above then the activation energy a reaction will occur.
When the activation energy is absorbed, a new arrangement of atoms occur.
This is called transition state, and its the state at which the reactants have the highest potential energy.
Bond breaking and forming occurs in this stage.
The size of activation energy indicates how easy it is for the reaction to occur. Hence reaction rate is also dependent on activation energy.
Changing concentration or pressure(Increasing reaction rate):
By increasing the concentration present you are increasing the number of particles present.
This allows for more collisions to occur which will also lead to more successful collisions.
For a reaction that is occurring in a gaseous phase, you can increase the pressure (same effect as increasing concentration).
Changing surface area:
Increasing the surface area increases the number of collisions. As there are more individual particles exposed, hence reaction rate increases.
Changing temperature:
As the temperature of the reactants increase the average kinetic energy of particles also increase, hence more collisions will have sufficient energy leading to more successful collisions.
Types of Catalyst:
Homogenous Catalyst: Same physical state as the reactants and products.
Heterogenous catalyst: Different physical state from the reactants and products.
What is a catalyst:
A catalyst provide a alternate reaction pathway that has a much lower activation energy. Lower the activation energy meaning more particles will have sufficient energy which means more successful collisions.
Enzymes vs Inorganic Catalyst:
Enzymes are biological catalyst made of proteins.
Enzymes are more selective catalyst, they catalyze a specific reaction.
Where as inorganic catalyst can be used to catalyze many reactions.
Enzyme work by forming an enzyme substrate complex.
Catalytic Convertors:
Catalytic converters in car exhausts are designed to remove pollutant gases such as carbon monoxide and nitrogen oxides from engine emissions, by converting them into non-toxic gases.
The gaseous reactants pass through a honeycomb structure, coated in particles of metals like platinum, palladium and rhodium; the catalysed reaction takes place on the surface of the metals.
This is an example of heterogeneous catalysis, where the reactants are in a different phase to the catalyst.
2NO(g) →N2(g)+ O2 (g)
2CO + O2(g) → 2CO2 (g)
