3.1.5 Kinetics Flashcards
What are the 5 main factors affecting rate of reaction?
- Conc.
- Pressure.
- Temp.
- SA.
- Catalyst.
Define rate of reaction.
- Change in conc of a reactant or product in a given period of time.
Define activation energy.
- Minimum amount of energy which reacting particles require for successful collision.
How does conc affect ror?
- Conc increase.
- More particles of reactant present.
- More successful collisions in given period of time.
- ∴ ror increases.
How does pressure affect ror?
- Pressure increase in gaseous reaction system.
- Particles forced closer together.
- Leads to more successful collisions in given period of time.
- ∴ ror increases.
How does temp affect ror?
- Temp increase, particles gain energy + move faster.
- More frequent successful collisions in given period of time.
- ∴ ror increases.
How does SA affect ror?
- Increasing SA increases exposed surface of reactants.
- Increase in number of successful collisions in given period of time.
- ∴ ror increases.
How do catalysts affect ror?
- Catalyst increase ror wo/ being used up.
- Provide alternative reaction pathway of lower activation energy.
- More successful collisions in given period of time.
- ∴ ror increases.
Why are catalysts important in industrial processes?
- Speed up reactions ∴ reduce costs.
What type of graph can be used to show exothermic and endothermic reactions?
- Enthalpy profile diagrams or reaction profile diagrams.
Draw an enthalpy diagram for an exothermic reaction.
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Draw an enthalpy diagram for an endothermic reaction.
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What is a Maxwell-Boltzmann distibution?
- Plot of number of gaseous molecules against energy at fixed temp.
What type of molecules is a Maxwell-Boltzmann distribution used for?
- Gaseous molecules.
What is a Maxwell-Boltzmann distribution also called?
- Molecular energy distribution graph.
- Distribution of molecular energies.
What is important about the temp in a Maxwell-Boltzmann distribution?
- Constant.
What does a Maxwell-Boltzmann distribution look like at a constant temp?
- Roughly normal distribution which is asymptotic to the horizontal axis.
What are the 5 main points from a Maxwell-Boltzmann distribution at constant temp?
- 0 molecules have 0 energy ∴ starts at origin.
- Area under graph = total no. molecules present.
- Peak is most probable energy of molecules (Emp).
- Most molecules have moderate energy in middle of graph.
- Very few molecules have high energy but asymptote as no upper limit to the energy of particles.
How is activation energy represented on a Maxwell-Boltzmann distribution?
- Ea.
What are on the x and y axis of a Maxwell-Boltzmann distribution?
- x –> Energy.
- y –> No. molecules.
Using a M-B distribution how does increasing a catalyst increase ror?
- More area above activation energy.
- ∴ more molecules w sufficient energy for successful collisions.
Does using a catalyst affect the shape of a M-B distribution?
- No bc total no. molecules + temp are same.
Does increasing temp affect the shape of a M-B distribution?
- Yes because increase in energy of reactants.
What 4 things should you note when sketching a distribution for the same sample of gas at a lower or higher temp?
- Lower –> distributions moved to left + peak is higher.
- Higher –> moved to right + lower peak.
- Graphs should only cross once.
- Curves always start at origin + are asymptotic.
Using a M-B distribution how does increasing temp affect ror?
- Higher temp, more area under graph at Ea
- ∴ more reactant molecules to undergo a successful collision.
- ∴ higher ror at higher temp.
What affect does a small increase in temp have on ror?
- Large increase in ror as significant increase in no. molecules w enough energy to undergo successful collisions.
Does increasing conc affect the shape of a M-B distribution?
- Same basic shape.
- Higher peak.
- Emp (most probable energy) in same place.
Using a M-B distribution how does increasing conc affect ror?
- Higher conc, higher no. reactant molecules.
- Overall area under increases.
- ∴ more shaded area above Ea.
- Increase in no. molecules which have energy to undergo successful collision increases.
- ∴ higher ror.
How is Ea affected by increasing conc?
- Higher conc more area of reactant molecules that have Ea.
Does incresing temp or conc have a more significant affect on ror?
- Increasing temp.
