Kinetics Flashcards
(18 cards)
Activation energy?
the minimum energy that colliding particles must have in order to react
What is the definition of rate of reaction?
the amount of substance formed per unit of time
What is the collision theory?
particles must COLLIDE before a reaction can take place but not all collisions lead to a reaction
Explain why most collisions do not lead to a reaction?
Not all the particles have greater or equal amount of energy to the activation energy
What is the effect of changes in pressure on collision frequency?
if pressure increases, less time is taken to reach equilibrium
-occurs at a faster rate
- particles are closer together
- more particles have energy that is greater or equal to activation energy
- increased frequency of successful collisions
- rate of reaction increases
if pressure decreases, more time is taken to reach equilibrium
-occurs at a slower rate
- particles are not closer together
- less particles have energy that is greater or equal to activation energy
- less frequent successful collisions
- rate of reaction decreases
What is the effect of changes in concentration on collision frequency?
- more frequent successful collisions
- more particles have energy that is greater or equal to activation energy
- rate of reaction increases
if concentration decreases, there are less particles within a given volume
- particles are not closer together
- less frequent successful collisions
- less particles have energy that is greater or equal to activation energy
- rate of reaction decreases
What is a Maxwell-Boltzmann distribution curve?
a curve which shows how energies of particles are distributed within a sample
Why does the curve start at zero?
as all gas particles have energy so if there are no gas particles, there is no energy
what does the area under the Maxwell- Boltzmann curve represent?
area under curve = total number of gas particles
What does the peak of the curve represent?
-EMP
- most probable energy that most of the particles have
• the mean energy of the molecules is greater than the most probable energy of the molecules
How does the Maxwell- Boltzmann curve look like if there is a higher temperature?
- lower peak
- curve shifts to the right of graph
How does the Maxwell- Boltzmann curve look like if there is a lower temperature?
- higher peak
- curve shifts to the left of graph
With use of the Maxwell-Boltzmann distribution, explain why a small temperature increase can lead to a large increase in rate?
There is a larger area under the curve therefore more particles have energy that is greater or equal to the activation energy.
Therefore, the frequency of successful collisions increases hence rate of reaction increases
What is a catalyst?
-substance that speeds up rate of reaction but is chemically unchanged
- provides an alternative route that lowers activation energy
With use of a Maxwell-Boltzmann distribution, explain how a catalyst increases the rate of a reaction involving a gas.
catalyst speed up the rate of reaction by providing an alternative route with lower activation energy.
- more particles have energy that is greater or equal to activation energy
- rate of reaction increases
Sample of gas molecules
At a given time their average kinetic energy is constant
Explain in general terms how a catalyst increases the rate of reaction
provides a different route
With lower activation energy
Explain qualitatively why doubling the temperature has a much greater effect on the rate of the reaction than doubling the concentration of E.
• Reaction occurs when molecules have E>Ea
• Doubling T by 10 °C causes many more molecules to have this E
• Whereas doubling [E] only doubles the number with this E
