10. Kinetics Flashcards
(18 cards)
What is chemical kinetics?
The study of rates of reaction.
Define “rate of reaction”.
A measure of the change in the concentration of a reactant or product with respect to time.
What is a catalyst?
A substance that increases the rate of a chemical reaction without itself being used up. It provides a reaction pathway that has lower activation energy.
Define “homogenous catalyst”.
A catalyst in the same state as the reactants and products, providing a pathway of lower activation energy by forming an intermediate.
Define “heterogenous catalyst”.
A catalyst in a different state to the reactants and products, working via chemisorption to provide a pathway of lower activation energy.
Define “activation energy”.
The minimum energy required by reactants for a reaction to occur.
Define “chemisorption”.
The process of adsorbing reactant molecules onto the surface of the catalyst, weakening bonds, and desorbing product molecules.
What factors affect the rate of reaction?
Temperature
Pressure
Concentration
Presence of a catalyst
How does temperature affect reaction rate?
Increasing temperature increases the energy of reacting particles, which leads to an increase in the number of collisions, causing an increase in the number of successful collisions in a given period of time, increasing reaction rate.
How does pressure affect reaction rate?
Increasing pressure pushes reacting particles closer together, which increases the number of collisions, causing an increase in the number of successful collisions in a given period of time, increasing the reaction rate.
How does concentration affect reaction rate?
Increasing concentration of the reactants increases the number of reacting particles, leading to an increased number of collisions, causing an increase in the number of successful collisions in a given period of time, increasing the rate of reaction.
How does the presence of a catalyst affect the rate of reaction?
A catalyst provides an alternative reaction pathway of lower activation energy, increasing the number of successful collisions, increasing the reaction rate.
How is the activation energy determined from an enthalpy-profile diagram?
The distance between the energy of the reactants to the highest point in the reaction pathway arc.
What is the difference between an enthalpy-profile diagram and a Maxwell-Bultzmann distribution?
An enthalpy-profile diagram shows how overall energy changes throughout a reaction.
A Maxwell-Boltxmann distribution shows the distribution of individual molecular energies.
Describe a Maxwell-Boltzmann distribution.
The number of gaseous molecules is plotted against the energy they possess, in a curve. No particles have no energy, so the curve begins at the origin. The highest point is the most likely energy of the particles. There is no upper limit to the amount of energy a particle can possess, so although the line gets lower, it does not touch the axis. The area under the graph is the total number of particles present.
How is activation energy shown on a Maxwell-Boltzmann distribution?
The symbol “Ea”, plotted on the x-axis, where every particle with this amount of energy or more is shaded to show that they are reacting, and everything below has too low of an energy.
How is catalysed activation energy shown on a Maxwell-Boltzmann distribution?
The symbol “Ea(cat)”, comparatively further left along the x-axis, showing that more particles have sufficient energy to react.
How does temperature affect the Maxwell-Boltzmann distribution?
Increasing temperature increases the energy of the gaseous reactant molecules, changing the shape of the curve.
A lower temperature has a higher, narrower peak further left.
A higher temperature has a lower, broader peak further right.
The same area is calculated overall.
