define activation enthalpy
the minimum energy that molecules must have in order to successfully collide and react
what does the boltzmann distribution curve represent
it shows how the kinetic energy of gas molecules are spread over a temperature
why does the Boltzmann distribution curve only apply to gases
because gases move randomly so each molecule will have a different KE value unlike liquids or solids which are in fixed positions
which gas molecules can react
those with kinetic energy greater than or equal to the activation energy
what four factors affect the Boltzmann distribution curve
-presence of a catalyst
-concentration of reactants
-temperature
-pressure
how does a catalyst affect the Boltzmann distribution curve
it increases the fraction of molecules with enough energy to react via lowering the activation enthalpy. This increases the number of successful collisions because more molecules have the minimum energy needed to react
how does increasing the conc. of reactants affect it
molecules are closer together on average which increases the rate of collisions, making them more likely to successfully collide
how does increasing the pressure affect it
molecules are closer together on average which increases the rate of collisions, making them more likely to successfully collide
how does temperature affect it
as temperature rises, a greater number of colliding molecules have kinetic energy greater than or equal to the activation energy. More molecules are moving faster, increasing the number of successful collisions because more molecules have the minimum energy needed to react
how can the affect of temperature be seen visually on the curve
the distribution curve shifts towards the right and broadens
define collision theory
A theory that states that chemical reactions can only occur when reacting particles collide with:
-energy equal to or greater than the activation energy
-The correct orientation
define homeogenous catalysis
The process of increasing the reaction rate using a catalyst which is in the same state as the reactants
what five factors affect the rate of reaction
-concentration of reactants
-temperature
-intensity of radiation(more dissociation)
-particle size of a solid, a powder reacts faster than a lump of solid=more SA
-presence of a catalyst
how do homogenous catalysts lower the activation enthalpy of a reaction
via the formation of one intermediate
why can homogenous catalysts form intermediates but heterogenous catalysts cant
because homogenous catalysts are in the same phase as the reactants, they can mix which makes it easy for the catalyst to temporarily bond with the reactant and form an intermediate
1) how is an intermediate formed
the catalyst reacts with a reactant to form an intermediate
2) how is the product formed(and the catalyst released)
the intermediate reacts with a reactant to form a product and release the catalyst
3) how does the formation of intermediates lower the overall activation enthalpy
each step has smaller enthalpy demands because all bonds dont need to break at once
draw the enthalpy profile diagram of homogenous catalysis
give five examples of experiments where the ROR can be calculated
-producing a volume of gas
-temperature change(endo or exo)
-calorimetry(amt of ppt formed)
-change in ph(acid-base)
-change in concentration of a solution(titrations)
whats the formula for calculating ROR from a graph
change in y over change in x
what axis is the dependent variable usually on
the x axis
what axis is the independent variable usually on
the y axis
