Kinetics Flashcards
What’s the formula for mean rate of reaction
Mean rate = volume of product/time (measured in cm3/s)
What’s the definition of activation energy
The minimum energy required for a reaction to occur
What factors affect rate of reaction (4)
- Temperature
- Concentration
- Pressure (gases only)
- Surface area
How does temperature affect rate of reaction
If the temperature is increased:
- Kinetic energy is increased
- This causes the particles to move faster
- Leading to more frequent and successful collisions
- Which increases the overall rate of reaction
If temperature is decreased, it’s the opposite (with many fewer collisions)
How does concentration affect rate of reaction
(Usually happens with aqueous solutions)
If concentration is increased:
- There’s an increase in the number of particles per given volume
- Meaning the particles are closer together
- This increases the chance of more frequent and successful collisions
- Therefore increasing overall rate of reaction
A decrease in concentration: opposite of increase
How does pressure affect rate of reaction
An increase in pressure:
- Increases the number of particles per given volume
- Meaning the particles are closer together
- This increases the chance of more frequent successful collisions
- Resulting in an overall increased rate of reaction
Decrease in pressure is the opposite
How can you increase the pressure (2)
- by increasing the number of particles per given volume
- by decreasing the volume
How does surface area affect rate of reaction
(Mainly for solids)
Increased SA:
- If you crush the solid, it increases the SA and therefore the particles have more area available for the reaction to take place
- This results in an increased rate of reaction
Rate of reaction product curve
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Rate of reaction reactants curve
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Why don’t particles move at the same rate
Particles in any gas/solution are constantly moving
They move at different rates because they contain different amounts of energy
Label a Maxwell boltsman distribution curve with an added catalyst
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Describe what happens to the MBD graph at a higher temperature
- Many more particles have activation energy or higher for the reaction to take place
- The area under the graph stays the same
- The curve shifts right and has a lower peak
*if temperature doubles, rate of reaction increases but if the concentration/pressure doubles, then the rate of reaction also doubles
What does the area under the MBD graph represent
The total number of particles in the reaction
What is the definition of rate of reaction
The change in concentration of product in a given time
Draw and label an exothermic reaction profile
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Draw and label an endothermic reaction profile with a catalyst
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What is a catalyst
Substances that increase the rate of chemical reactions without being chemically changed or used up (they’re unreactive)
How do catalysts increase rate of reaction (2)
- They decrease activation energy
- By providing an alternative pathway
Why are transition metals good catalysts
They have variable oxidation states
What are zeolites
Minerals that have an very open pore structure that ions/molecules can fit into (creates a very large surface area)
What is a heterogenous catalyst
A catalyst that’s in a different phase from the reactants (different state)
(Reaction occurs at active sites on the surface)
Why do catalysts need replacing & what is the impact of this
Catalysts can become poisoned by impurities that block the active sites and cause them to have reduced efficiency
This has a cost implication as they need to be replaced which can be expensive
Explain how heterogenous catalysts work and give an example of how one is used in a reaction
- Reactants are brought together which increases the concentration on the surface of the catalyst
- Reactants must be correctly orientated
- Reactants adsorb onto the surface of the catalyst
- The 2nd reactant binds to the first
- Bonds broken and made, the transition state starts to emerge
- The products then desorb from the surface
E.g iron catalysts the harbour process
Why do different catalysts have different activities
(Activity is linked to the strength of adsorption)
If adsorption is too strong, the products won’t desorb
If adsorption is too weak, the reactants aren’t brought together
What is a free radical
A species with an unpaired electron
How is ozone continually broken down and reformed (3 equations)
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What is homolytic fission
When the covalent bond splits evenly (an unpaired electron goes to each side of the covalent bond)
Why are chlorofluorocarbons dangerous
They continue to breakdown the ozone as the free radicals (which are very reactive), are regenerated
Reaction with a CFC and ozone (include reaction summary and steps)
- Initiation
2a. Propagation
2b. Propagation - Termination
