Collision theory Term 1 Flashcards
Examples of rapid reactions
acid base, ionic (precipitation)
Examples of slow reactions
breaking and forming of covalent bonds (large molecules)
7 ways to measure reaction rate
-mass lost by regency
-mass gained by product
-volume of gas
-pressure of gas
-colour intensity
-solution concentration
-pH
What is the collision theory?
For a successful collision to occur reactant particles must collide with:
-sufficient energy
-correct orientation
Define theory of orientation
Particles only collide with suff. energy if done with correct orientation for bond break/form of new chemical bond.
How does orientation occur? Can it be modified?
Result of random movement
-not easily modified
-less reactive site=less collisions
Define theory of sufficient energy
Reactant particles require certain amount of kin. energy for collision to be successful and generate products
Why do particles have differing kinetic energies? How is this shown?
Due to movement at differing velocities
-illustrated by kinetic energy distribution diagram
What is a Maxwell-Boltzmann/Ek distribution diagram?
Shows range of Ek energies possessed by particles in substance at a specific temperature
What can be seen on Ek diagrams?
-zero particles with no kinetic energy
-many particles with moderate kinetic energy
-few particles with high level kinetic energy
Define activation energy? How will a reaction occur due to this?
The minimum amount of energy required to break existing chemical bonds to allow for successful collisions
-potential reaction will occur if energy is greater or equal to Ea
Define transition state
The highly energised/unstable arrangement of reactant particles where bond break/form occurs
What occurs in reverse reactions?
Activation energy plus enthalpy change=new Ea
What is the difference between energy profile and kinetic energy distribution diagrams?
EP=reaction journey of individual atoms
EkDD=Overall picture of particles potentially in reaction
What influences reactions rate
concentration, temperature, pressure, the presence of a catalyst and surface area of reactants
3 things increasing collision frequency?
SA, concentration, gas pressure
Define surface area. Effect on reaction rate.
Area of the chemical substances used in a chemical reaction
-particles on surface are available to collide w/other reactants (number of part. depends on SA)
-surface area is a consequence of particle size (subdivision)
-allows for more reactant particles to collide
-frequency of collision increase=high number of successful collision per unit time
-hence, increased r+r
Define concentration. Effect on reaction rate.
Number of particles per unit volume.
-high conc of solute dissolved in solution=increase frequency of collisions due to increase particle vol.
-due to increase collisions=increase in % of successful collisions
-result in greater number of successful collisions per unit time
-thus, increase r+r
Define pressure. Effect on reaction rate.
Force per unit area that gas particles exert when they collide w/wall of their container.
-increase gas pressure occurs due to increase number of gas particles in given vol. at constant temp. or increase vol and same particle number
-produces increase frequency of collisions per unit time
-increases %success. collisions =increased successful collisions per unit time
-increases r+r
Define partial pressure. What is total pressure then?
Pressure exerted by 1 component of a gas mixture
-total pressure of mixture is equal to the sum of individual partial pressures of each component
2 things increasing sufficient energy.
Temperature and presence of a catalyst
Define temperature in relation to speed. Effect on r+r.
Measure of average kinetic energy of all atoms or molecules of a substance
-increase in temperature corresponds w/increase kinetic energy of particles
-increase temp=increase average Ek
-therefore increases frequency of collisions due to increased speed
- greater % of successful collisions
-therefore, successful collision increase per unit time
-thus, increase r+r
Define catalyst. How does presence effect r+r.
Substance providing alternative reaction pathway w/lower activation energy.
-increases % of particles that have greater or equal energy to activation energy
-greater proportion of collision are successful per unit time
-reaction rate increases
What occurs to a reaction over time? In terms of speed and conc
They do not proceed at a steady rate. They decrease in speed overtime.
-as reaction progresses conc of reaction decreases
-this reduces frequency of collisions between particles and so the reaction slows down
Define enthalpy
Measure of the heat content of a substance at constant pressure
Define temperature in relation to activation energy. Effect on r+r.
Measure of average kinetic energy of all atoms or molecules of a substance
-increase in temperature corresponds w/increase kinetic energy of particles
-increase temp=increase average Ek
-this means greater % of particles with energy greater than activation energy which overcomes the activation energy barrier
-therefore increases proportion of particles with sufficient energy to collide =successful collisions increase per unit time
-thus, increase r+r
Definition for partial pressure
total pressure of a mixture of gases is equal to the sum of the partial pressures of it’s components
i.e. the sum of pressure that each component would exert if it were present alone and occupied the same volume as the mixture of gases
What causes change in concentration?
increase or decrease in partial pressure changes conc
