Kinetics Flashcards
Collision theory (2)
Reactions can only occur when collisions take place with enough activation energy
They must also collide at the correct orientations for a reaction
Define activation energy
The minimum energy at which particles need to start to reaction and break the relevant reactant bonds
what does the Maxwell Boltzman distribution show?
The distribution shows the spread of energy that molecules are gas or liquid have a particular temperature.
what is on the axes of the Maxwell Boltzmann distribution?
Number of molecules with this energy on y axis
Energy on x axis
Why does the distribution curve go through the origin?
there are no molecules with no energy
Where is the mean on the maxwell boltzmann distribution curve?
To the right of the peak, which is the Emp - most probable energy
Why do some molecules have low energy on the MB Distribution?
Some collisions cause some particles to slow down
What does the area under the MB Distribution curve represent?
The total number of particles present
What to remember about drawing the end of the MB distribution?
Never let energy distribution meet the x axis aside from the origin as there is no maximum energy for molecules
How can a reaction go to completion if few particles have energy greater than Ea?
particles gain energy through collisions
As temperature increases, what does the MB distribution shift towards?
towards having more molecules with higher energies
what happens when the temperature is increased in the MB distribution?
at higher temperatures both the Emp and mean energy shift to higher energy values, although the number of molecules with those energies decrease
more molecules have the activation energy or greater
define rate of reaction
The rate of reaction is defined as a change in concentration of a reactant or product in a unit time
how do you find the rate of reaction from a graph with concentration of reactant on the Y axis and its time on the X axis? what about initial rate?
find a gradient of the curve by drawing a tangent
at the start of the reaction
what are the effects of increasing concentration/pressure on rate?
there are more the number of particles per unit volume, so the particles collide with the greater frequency, and there will be a higher frequency of effective collisions
what are the effects of increasing concentration/pressure on the MB distribution curve?
The shape of the energy distribution curve does not change
The curves will overall be higher and the area under the curve will be greater because there are more particles
does increasing concentration/pressure have an effect on the proportion of particles with energy higher than activation energy?
No
in rates curves, what do different volumes of the same initial concentrations have in common?
The same initial rate and initial gradient, provided everything else is the same
what is the effect of increasing temperature on the MB distribution curve?
as temperature increases a significantly bigger proportion of particles have an energy greater than Ea on the graph, so the frequency of successful collisions increases
what is the effect of increasing surface area on a reaction’s rate?
successful collisions will occur more frequently between the reaction particles, and this increases rate of reaction
Define catalyst
The substance that increases its reaction right without being used up in the reaction by providing an alternate route, with a lower activation energy
how does a catalyst increase rate of reaction?
as the Ea is now lower more particles have an energy that’s greater than Ea so there will be a higher frequency of effective collisions
