Kinetics. Flashcards
What is meant by collision theory.
A theory used to describe chemical reactions using rate and energy of collisions.
What two requirements must reacting particles meet in order for them to react.
They must collide with enough energy to break bonds and also between parts of the molecule that are going to react together.
Therefore have the activation energy and also correct orientation orientation.
Where is the Emp and mean energy found on a Maxwell Boltzmann distribution. Define both of these terms.
Emp this is the most probable energy (not the same as mean energy) and is found at the curves peak.
Then slightly to the right in a way that divides the area under the graph into half is the mean energy.
What happens to species that are at the top of an enthalpy diagram.
They are called a transition state or activation complex and there are bonds being made and broken , this creates extra enemy and makes such species unstable.
What should be on the x and y axis of a Maxwell boltzman distribution.
On Y : fraction of particles with energy E
On x : Energy E
What type of energies do most particles have on a Maxwell boltzman distribution. Comment also on the shape of the curve.
Most particles have intermediate energies around the peak of the curve.but the distribution is not symmetrical (normal).
Explain why the energy distribution on a Maxwell-Boltzman curve goes through the origin and has no upper limit.
This is as no particles have no energy and very few particles have high energy on the curves right hand side , there is no maximum energy (E) the particles can have and so the curve has no upper limit.
How can a reaction go to completion if few particles have energy greater than EA?
Particles can gain energy through collisions.
Why do a few particles have low energies on the MB energy distribution curve.
A few have low energies because collisions cause some particles to slow down
How many particles have energy greater than EA.
Only a few particles have energy greater than the EA
What does the area under the curve of a MB energy distribution represent.
The area under the curve represents the total number of particles present
What happens to the key values on a MBD when the temperature is increased. State also how the number of molecules that have such new values changes.
As the temperature increases the distribution shifts towards having more molecules with higher energies as you would expect. SO….
At higher temps both the Emp and mean energy shift to higher energy values, although the number of molecules with those energies decrease. There is a wider spread of energies.
Why should the total area under the curve should remain constant.
The total area under the curve should remain constant
because the total number of particles is constant.
Comment on the range of energies at higher temperatures compared to that of lower temperatures.
At higher temperatures the molecules have a wider
range of energies than at lower temperatures.
Explain the need of energy to start a reaction and also define activation energy in your answer.
Reactions can only occur when collisions take place between particles having sufficient energy. The energy is usually NEEDED TO BREAK THE RELEVANT BONDS in one or either of the reactant molecules.
This minimum energy is called the activation energy. The activation energy, EA, is defined as the minimum energy which particles need to collide and have a successful collision.
Define the rate of reaction.
The rate of reaction is defined as the change in concentration of a substance in unit time , Its usual unit is mol dm-3s-1 .
When measuring reaction rates if a graphical method was to be used how cloud reaction rate be calculated. A reaction where the change in concentration isn known.
When a graph of concentration of reactant is plotted vs time, the gradient of the curve is the rate of reaction.Reaction rates can be calculated from graphs of concentration of reactants or products, by drawing a tangent to the curve (at different times) and calculating the gradient of the tangent.
