Collision theory Term 1

Question 1

Examples of rapid reactions

Answer 1

acid base, ionic (precipitation)

Question 2

Examples of slow reactions

Answer 2

breaking and forming of covalent bonds (large molecules)

Question 3

7 ways to measure reaction rate

Answer 3

-mass lost by regency
-mass gained by product
-volume of gas
-pressure of gas
-colour intensity
-solution concentration
-pH

Question 4

What is the collision theory?

Answer 4

For a successful collision to occur reactant particles must collide with:
-sufficient energy
-correct orientation

Question 5

Define theory of orientation

Answer 5

Particles only collide with suff. energy if done with correct orientation for bond break/form of new chemical bond.

Question 6

How does orientation occur? Can it be modified?

Answer 6

Result of random movement
-not easily modified
-less reactive site=less collisions

Question 7

Define theory of sufficient energy

Answer 7

Reactant particles require certain amount of kin. energy for collision to be successful and generate products

Question 8

Why do particles have differing kinetic energies? How is this shown?

Answer 8

Due to movement at differing velocities
-illustrated by kinetic energy distribution diagram

Question 9

What is a Maxwell-Boltzmann/Ek distribution diagram?

Answer 9

Shows range of Ek energies possessed by particles in substance at a specific temperature

Question 10

What can be seen on Ek diagrams?

Answer 10

-zero particles with no kinetic energy
-many particles with moderate kinetic energy
-few particles with high level kinetic energy

Question 11

Define activation energy? How will a reaction occur due to this?

Answer 11

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

Question 12

Define transition state

Answer 12

The highly energised/unstable arrangement of reactant particles where bond break/form occurs

Question 13

What occurs in reverse reactions?

Answer 13

Activation energy plus enthalpy change=new Ea

Question 14

What is the difference between energy profile and kinetic energy distribution diagrams?

Answer 14

EP=reaction journey of individual atoms
EkDD=Overall picture of particles potentially in reaction

Question 15

What influences reactions rate

Answer 15

concentration, temperature, pressure, the presence of a catalyst and surface area of reactants

Question 16

3 things increasing collision frequency?

Answer 16

SA, concentration, gas pressure

Question 17

Define surface area. Effect on reaction rate.

Answer 17

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

Question 18

Define concentration. Effect on reaction rate.

Answer 18

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

Question 19

Define pressure. Effect on reaction rate.

Answer 19

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

Question 20

Define partial pressure. What is total pressure then?

Answer 20

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

Question 21

2 things increasing sufficient energy.

Answer 21

Temperature and presence of a catalyst

Question 22

Define temperature in relation to speed. Effect on r+r.

Answer 22

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

Question 23

Define catalyst. How does presence effect r+r.

Answer 23

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

Question 24

What occurs to a reaction over time? In terms of speed and conc

Answer 24

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

Question 25

Define enthalpy

Answer 25

Measure of the heat content of a substance at constant pressure

Question 26

Define temperature in relation to activation energy. Effect on r+r.

Answer 26

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

Question 27

Definition for partial pressure

Answer 27

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

Question 28

What causes change in concentration?

Answer 28

increase or decrease in partial pressure changes conc