Reaction rates Flashcards
What does a Boltzmann distribution show?
A Boltzmann distribution shows how energy varies over molecules in a substance.
How does temperature affect the rate of reaction?
Increase in temperature.
Increase in kinetic energy.
Particles more faster.
There will be more successful collisions and hence more reactions take place.
How does a catalyst affect the rate of reaction?
A catalyst increases the rate of reaction by providing an alternate reaction pathway with a lower activation energy.
How does increasing concentration affect the rate of reaction?
Particles are closer; more frequent collisions; increase in rate of reaction.
What are the key principles of a Boltzmann distribution?
The curve starts at the origin because there are no molecules that have zero energy (all molecules must have some energy).
The curve does not touch the x-axis at high energies because there is no maximum energy that molecules can have.
The area under the graph represents the total number of molecules.
How does a Boltzmann distribution change is temperature is increased?
The graph shifts to the right so there is a greater proportion of molecules that have energy higher than activation energy. However, the area under the graph does not change as the total number of molecules stay the same. The graph also has a slightly lower peak.
What are the key principles of Collision Theory?
A reaction won’t take place between two particles unless:
They collide in the right direction/orientation.
They collide with at least a minimum amount of kinetic energy.
What is the definition of a catalyst?
A catalyst increases the rate of reaction by providing an alternate reaction pathway that has a lowered activation energy. The catalyst remains chemically unchanged at the end of the reaction.
How does a Boltzmann distribution change in the presence of a catalyst?
The shape of the graph remains the same. Although, the point at which the activation energy is at shifts to the left. This means there is a greater proportion of molecules with activation energy.
How does the peak of an enthalpy profile diagram change with a catalyst?
The peak of the enthalpy profile diagram is lowered due to a lowered activation energy. Remember: the distance from the reactants to the peak of the curve is the activation energy.
What is a heterogenous catalyst?
A heterogenous catalyst is a catalyst that is in a different physical state to reactants. The reaction takes place on the surface of the catalyst, so increasing surface area increases ROR.
What is a homogenous catalyst?
A homogenous catalyst is a catalyst that is in the same physical state as reactants. A homogenous catalyst works by forming intermediate species.
What are the benefits of catalysts?
Reactions happens in shorter time.
Production costs for industries are lowered.
Energy is saved.
Less carbon dioxide is released.
Fossil fuels are preserved.
What is dynamic equilibrium?
Dynamic equilibrium is when the rate of the forwards reaction is equal to the rate of the backwards reactions.
At dynamic equilibrium, concentration of reactants and products stay constant.
Dynamic equilibrium can only occur in closed systems.
What is Le Chatelier’s principle?
Le Chatelier’s principle states that if there were to be a change in concentration, pressure or temperature, the equilibrium will move to help counteract that change.
