reaction kinetics

Question 1

Definition of catalyst

Answer 1

Substance that increases the rate of reaction by providing an alternative reaction pathway with lower activation energy

Question 2

Activation energy definition

Answer 2

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

Question 3

Why does the reaction rate increase when temp increases by use of maxwell-boltzmann distribution curve

Answer 3

When temp increases, the average KE of the reactant particles increase more reactant particles have energy greater than or equal to the activation energy of rxn, shown by larger shaded area at a higher temp
Increase in effective collision frequency, increase rate in reaction

Higher temp also results in larger rate constant k hence increased rate of reaction

Question 4

How to make use of Maxwell- Boltzmann distribution curve to explain now a catalyst increases rate of reaction

Answer 4

Catalyst increases the rate of reaction by providing an alternative reaction pathway with lower activation energy
More reactant molecules have energy greater than or equal to the activation energy for catalysed rxn, shown by larger shaded area for catalysed rxn in diagram
Increase in effective collision frequency, increased rate of reaction
Alternative reaction pathway results in large rate constant K increased rate of reaction

Question 5

Describe use of catalysts in a reaction between ions

Answer 5

Uncatalysed reaction: direct reaction between reactant anions,
Electronic repulsion bein the reactant anions results in high activation energy and slow reaction
Catalysed reaction: each step involves a reaction between oppositely charged tons when have a natural tendency to attract each other, lowering activation energy and increases reaction rate

Question 6

J describe mode of action of heterogenous catalyst

Answer 6

1. Reactant molecules diffuse to catalyst surface and are adsorbed to active sites of catalyst
2. Adsorption weakens the covalent bonds within the reactant molecules, lowering activation energy
3. Concentration of reactant molecules at catalyst surface increases
4. Reactant molecules can come in close contact with proper orientation
5. Product molecules desorb and diffuse away from the catalyst surface

Question 7

Describe autocatalyst at points of graph

Answer 7

1. Tangent is gentle; Initially, reaction is slow since if has a high activation energy
2. Tangent is steep: As the ions are produced, they increase rate of reaction by acting as an autocatalyst, providing an alternative pathway with lower activation energy
3. Tangent is gentle; Towards the end of reaction the concentration of the reactants has fallen to a low level and sotterate of the reaction decreases even though there is adequate supply of catalyst

Question 8

Describe enzyme-catalysed reaction

Answer 8

1. Rate of reaction increasing: at low substrate concentration, not all of active sites are occupied, rate is proportional to substrate concentration, reaction is first order with respect to the substrate
2. Rate of reaction plateaus: at high [substrate], the active sites of enzyme are saturated with substrate, increase in [substrate] has no effect on reaction rate, reaction is zero order with respect to substrate