Kinetics Flashcards
What are two definitions for rate of reaction?
- a measure of how fast the reactants are changing into products
- the amount of a reactant used up over time or the amount of product formed over time
How can u measure the rate of reaction if the reaction produces a gas?
- volume of gas at equal time intervals
- loss of mass as gas forms
Collision theory states that for two particles to react:
- they must collide with each other
- they must collide with the activation energy (the minimum energy for a reaction to happen)
- they must collide in correct orientation
Why is the reaction fastest at the start?
- lots of HCl acid particles available for marble chips to collide with
- higher frequency of successful collisions so rate is fastest
What is collision theory?
States for two particles to react:
- they must collide with each other
- they must collide with the activation energy
- they must collide in correct orientation
Why does the reaction slow down?
- hydrochloric acid particles have reacted with marble chips
- less available for collisions
- lower frequency of successful collisions so rate is slower
Why does the reaction end?
- all hcl particles are used up
- none available to collide with chips
- no successful collision
- reaction overt
What are the 4 conditions that effect rate of reaction?
- Surface area
- Concentration
- Temperature
- Adding a catalyst
Why does increasing the surface area of a solid increase the rate of reaction?
- larger area of solid particles are exposed
- increase in frequency of collisions
Why does increasing the concentration of a solution increase the rate of reaction?
- increasing the concentration of a solution means there is an increase of particles in a given volume
- increase in successful collisions
(Same as pressure)
What has the biggest impact on rate?
- increasing the temp
Why does increasing temperature have the greatest effect on rate?
- not only increases frequency of collisions
- energy with which the particles collide
How does increasing yhe temperature increase the rate of a reaction?
- increasing the temp increases the kinetic energy of they particles so they move faster
- many more particles have energy higher than or equal to the activation energy so a higher proportion of collisions are successful
- increase in frequency of successful collisions
What is a catalyst?
- a substacne that increases rate of reaction without being used up
How do catalysts work?
- by providing an alternative reaction pathway with a lower activation energy
- this means many more particles have energy higher than that of the activation energy so higher proportion of collisions are successful
- increase in frequency of successful collisions
What is maxwell-Boltzmann distribution?
- graphical representation of the energy distribution between particles within a system
Describe the axis of the Maxwell-Boltzmann distribution
- energy against number of particles
What does the curve starting at the origin show?
- no particles have 0 energy
Why do some particles have very low energies?
- particles collide with each other which slows them down
What is the peak of the curve?
- most probable energy
What does the point right of the peak of the curve show?
- mean energy of the particles
What is activation energy
- maximum energy required for reaction to happen, only particles with E>Ea react
Why does the curve descend asymptotically to zero?
- Very few particles have high energies
- theoretical maximum is infinity but probability is >0
What is the area under the curve?
- total number of particles
What will happen to the MBD if you increase the temperature
- Most probable energy - increase (shift right)
- The avg energy - increase (shift right)
- the number of particles with E>Ea - shift right
- Area under the curve - same
- height of the peak - flatter
What will happen to MBD if you decrease the temperature
- most probable energy will decrease (shift left)
- the average energy will decrease (shift left)
- the number of particles with E>Ea will decrease
- area under the curve will be the same
- the height of the peak will be taller
What does increase concentration/pressure do to the MBD?
- The most probably energy - more particles same energy
- the average energy - more particles, same energy
- the number of particles with E>Ea - more
- area under the curve - more
- the height of the peak - more
Why is increase the concentration the same as increasing pressure
- Increasing the concentration is achieved by increasing the pressure which in turn is achieved by decreasing the volume of the container
What will happen to the MBD when decreasing the concentration?
- most probably energy - same fewer particles
- the average - same fewer particles
- the number of particles with E>Ea - fewer
- area under the curve - less
- height of the peak - lower
What will happen to MBD when a catalyst is added?
- the most probably energy - same
- the average energy - same
- the value of the activation energy - lower
- the number of a particles with E>Ea higher
- area under the curve - same
- height of the peak - same
