Kinetics Flashcards
what is the collision theory
The collision theory states that for a chemical reaction to take place the particles need to collide with each other in the correct orientation and with enough energy in order to react
what happens to the bonds in reactions
they are made or broken
if molecules collide at high speeds, then (bonds)
the bonds can be broken and made
what constitutes to an unsuccessful collision
An ineffective collision is when particles collide in the wrong orientation or when they don’t have enough energy and bounce off each other without causing a chemical reaction
what is orientation
reactant molecules must collide with “favorable” orientation such that there is direct contact between the molecules to induce the breaking or forming of a bond in space
ie the same charge cannot be together as it will repel.
what diagram is used to show the progress of a reaction
a reaction profile
what is activation energy
the minimum energy with which particles need to collide to cause a reaction
what is the symbol for activation energy
Ea
Reaction profile for endo and exo
In exothermic reactions the reactants are higher in energy than the products
In endothermic reactions the reactants are lower in energy than the products
what is the purpose of catalysts
A catalyst is a substance that increases the rate of reaction without taking part in the chemical reaction by providing the particles an alternative mechanism with a lower activation energy
what is the Maxwell-Boltzmann energy distrubution
A Maxwell-Boltzmann distribution curve is a graph that shows the distribution of energies at a certain temperature
what does the M-B graph show
The graph shows that only a small proportion of molecules in the sample have enough energy for an effective collision and for a chemical reaction to take place
what is the effect of temp on the M-B graph
When the temperature of a reaction mixture is increased, the particles gain more kinetic energy
This causes the particles to move around faster resulting in more frequent collisions
Furthermore, the proportion of successful collisions increases, meaning a higher proportion of the particles possess the minimum amount of energy (activation energy) to cause a chemical reaction
With higher temperatures, the Boltzmann distribution curve flattens and the peak shifts to the right
how does temp increase rate
Therefore, an increase in temperature causes an increased rate of reaction due to:
There being more effective collisions as the particles have more kinetic energy, making them move around faster
A greater proportion of the molecules having kinetic energy greater than the activation energy
how do reactions with low Ea carry out
they are faster as less temp is needed so the particles have a lower energy that they need to get to to react
these molecules have above threshold energy
