1.5 Kinetics Flashcards
What is activation energy, Ea?
The minimum energy which particles need to collide to start a reaction.
Draw and label a Maxwell Boltzmann distributions.
How can a reaction go to completion if few particles have energy greater than Ea?
Particles can gain energy through collisions
What happens to a Maxwell-Boltzmann distribution curve if temperature is increased?
As the temperature increases the distribution shifts towards having more molecules with higher energies.
What happens to the most probable energy and mean energy as temperature increases?
At higher temps the Emp and mean energy shift to higher energy values, although the number of molecules with those energies decrease
What happens to the total area under the curve as temperature increases?
The total area under the curve should remain constant because the total number of particles is constant.
What happens to the range of energies on a Maxwell Boltzmann distributions curve when temp is increased?
At higher temperatures, the molecules have a wider range of energies than at lower temperatures.
Define rate of reaction
The change in conc of a substance in unit time. Usual unit = moldm-3s-1
Whats the effect on rate if you increase concentration or pressure?
At higher conc (or pressure) there are more particles per unit volume and so the particles collide with great frequency and therefore there will be a higher frequency of effective collisions. Therefore increased rate.
What does collision theory state?
For a reaction to occur successfully, these collisions must have greater than or equal to the activation energy of the reaction and the particle orientation must be correct.
What happens if the concentration is doubled?
Double the number of particles per unit volume and double the frequency of effective collisions
What happens to the Maxwell Boltzmann distributions curves shape if conc is increased?
The shape of the energy distribution curves do not change so the Emp and mean energy do not change. However, the curve will be higher, and the area under the curve will be greater because there are more particles.
Whats the effect on rate if the temperature is increased??
The energy of particles increases. Therefore the particles collide more frequently and more often with energy greater than the activation energy. Therefore the frequency of successful collisions increases, and in turn rate.
What does the Maxwell Boltzmann distributions curve show when temp in increased?
A significantly bigger proportion of particles have energy greater than the activation energy.
In an investigation of the rate of reaction between hydrochloric acid and pure magnesium, a student obtained the following curve.
The reaction of magnesium with dilute hydrochloric acid is exothermic.
Use your understanding of collision theory to explain why the student did not obtain a straight line.
As concentration increases the amount of heat given out increases
More successful collisions
ncreases the rate of a reaction
Draw a Maxwell Boltzmann distribution that shows the effect of a catalyst.
