OZ efgh: Kinetics; catalysis Flashcards
Name 5 methods of analysis which are used to measure rate of reaction.
- Titration (redox / acid-base)
- Colorimetry
- pH measurement
- Volume of gas evolved
- Mass change
How does quenching work?
- Sample isolated from reaction mixture
- Chemical added which stops reaction (e.g. neutralises a catalyst)
- Sample titrated to find conc. of a reactant/product
Define activation enthalpy.
The minimum energy that pairs of colliding molecules must have in order to react.
List 5 factors which affect the rate of reactions.
- Concentration / pressure
- Temperature
- Surface area
- Catalysis
- Radiation intensity
What is a catalyst?
A substance which increases the rate of a reaction, by providing an alternative pathway of lower activation enthalpy, but which remains chemically unchanged.
Explain why increasing concentration or pressure increases the rate of a reaction.
- More molecules per unit volume
- Higher probability that two molecules will collide with at least the activation enthalpy
- More successful collisions per unit time: rate increases
On the same axes, draw and label an enthalpy profile for:
- An uncatalysed exothermic reaction
- The same reaction, catalysed
State what occurs during the transition state of a reaction.
Bonds break and new ones form.
This graph shows the distribution of kinetic energies in molecules of gas at a certain temperature. What is this type of graph called?
A Boltzmann distribution.
Explain the qualitative effect of increasing temperature on the rate of a reaction. Include a Boltzmann distribution diagram in your answer.
- Peak approaches Ea and curve becomes more symmetrical
- Greater proportion of molecules have higher KE
- Higher probability that two molecules collide with at least the activation enthalpy
- More successful collisions per unit time: rate increases
Area is unchanged since the number of particles is constant
Explain the qualitative effect of catalysis on the rate of a reaction. Include a Boltzmann distribution diagram in your answer.
- Catalyst provides an alternative pathway of a lower activation enthalpy
- At a given temperature, there is a higher probability that two molecules will collide with at least Ea
- More successful collisions per unit time: rate increases
Is bond breaking exothermic or endothermic?
Endothermic
What is the effect of catalysing a reversible reaction?
- No effect on equilbrium position (i.e. concentrations) or Kc (i.e. relative rates at equilibrium)
- Increases rate at which equilibrium is attained
What is homogeneous catalysis?
Reactants + catalyst are in same physical state.
What does homogeneous catalysis generally involve?
Catalyst forms intermediate with reactants (transition state), which breaks down to give product + reformed catalyst.
