Reaction kinetics

Question 1

Concentration of reactants

Answer 1

• concentration increases
• reactant particles come closer together
• frequency of collisions increases
• frequency of effective collisions increases

Question 2

pressure of gas

Answer 2

• number of particles per unit volume increases
• frequency of collisions increases
• frequency of effective collisions increases

Question 3

when does rate constant increase

Answer 3

• temperature increase
• catalyst present

Question 4

Activation energy

Answer 4

The minimum amount of energy that the reactant particles must possess before their collisions can result in a reaction

Question 5

Effect of temperature on reaction rate

Answer 5

temperature increases
- average KE of reactant particles increases
- more particles have energy equal or greater than the activation energy of the reaction
- increase in frequency of effective collisions
- increase rate of reaction
- oso results in an increase in rate constant –> higher rate of reaction

Question 6

Effect of catalyst on reaction rate

Answer 6

• catalyst increases the rate of reaction by providing an alternative reaction pathway, one of lower activation energy
• more reactant particles have energy greater than or equal to the activation energy of the catalysed reaction
• increase in frequency of effective collisions
• increase in rate of reaction
• also results in an increase in rate constant k –> higher rate of reaction

Question 7

How heterogeneous catalysis works

Answer 7

1. Diffusion
   - reactant molecules diffuse towards the catalyst surface
2. Adsorption
   - reactant molecules adsorbed into active sites of the catalyst surface
   - this increases the concentration of the reactants at the catalyst surface
   - weakens the covalent bonds in molecules
3. Reaction
   - adjacent reactant molecules react to form molecules.
   - this reaction has lower activation energy than the uncatalysed reaction
4. Desorption
   - product molecule eventually breaks free from the catalyst surface
5. Diffusion
   - product molecules now diffuse away. vacant active sites are now available for adsorbing other molecules.

Question 8

Autocatalysis

Answer 8

• Initially, the reaction is slow due to the high activation energy.
• Mn2+ ions are produced
• rate of reaction increases as Mn2+ acts as autocatalyst, providing an alternate pathway with lower activation energy
• towards the end, the concentration of the reactants has fallen to a low level so the rate of reaction decreases

Question 9

Order of reaction

Answer 9

The order of reaction with respect to a given reactant is the power to which the concentration of that reactant is raised in the rate equation.

Question 10

rate constant

Answer 10

The rate constant of a reaction is the constant of proportionality in the rate equation of the reaction.

Question 11

half-life

Answer 11

The half-life of a reaction is the time taken for the concentration of a reactant to decrease to half its initial value.