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Chemistry ER > Kinetics > Flashcards

Kinetics Flashcards

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1
Q

What’s the formula for mean rate of reaction

A

Mean rate = volume of product/time (measured in cm3/s)

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2
Q

What’s the definition of activation energy

A

The minimum energy required for a reaction to occur

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3
Q

What factors affect rate of reaction (4)

A
  • Temperature
  • Concentration
  • Pressure (gases only)
  • Surface area
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4
Q

How does temperature affect rate of reaction

A

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)

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5
Q

How does concentration affect rate of reaction

A

(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

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6
Q

How does pressure affect rate of reaction

A

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

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7
Q

How can you increase the pressure (2)

A
  • by increasing the number of particles per given volume
  • by decreasing the volume
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8
Q

How does surface area affect rate of reaction

A

(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

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9
Q

Rate of reaction product curve

A

.

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10
Q

Rate of reaction reactants curve

A

.

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11
Q

Why don’t particles move at the same rate

A

Particles in any gas/solution are constantly moving
They move at different rates because they contain different amounts of energy

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12
Q

Label a Maxwell boltsman distribution curve with an added catalyst

A

.

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13
Q

Describe what happens to the MBD graph at a higher temperature

A
  • 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

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14
Q

What does the area under the MBD graph represent

A

The total number of particles in the reaction

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15
Q

What is the definition of rate of reaction

A

The change in concentration of product in a given time

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16
Q

Draw and label an exothermic reaction profile

A

.

17
Q

Draw and label an endothermic reaction profile with a catalyst

A

.

18
Q

What is a catalyst

A

Substances that increase the rate of chemical reactions without being chemically changed or used up (they’re unreactive)

19
Q

How do catalysts increase rate of reaction (2)

A
  • They decrease activation energy
  • By providing an alternative pathway
20
Q

Why are transition metals good catalysts

A

They have variable oxidation states

21
Q

What are zeolites

A

Minerals that have an very open pore structure that ions/molecules can fit into (creates a very large surface area)

22
Q

What is a heterogenous catalyst

A

A catalyst that’s in a different phase from the reactants (different state)
(Reaction occurs at active sites on the surface)

23
Q

Why do catalysts need replacing & what is the impact of this

A

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

24
Q

Explain how heterogenous catalysts work and give an example of how one is used in a reaction

A
  • 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

25
Q

Why do different catalysts have different activities

A

(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

26
Q

What is a free radical

A

A species with an unpaired electron

27
Q

How is ozone continually broken down and reformed (3 equations)

A

.

28
Q

What is homolytic fission

A

When the covalent bond splits evenly (an unpaired electron goes to each side of the covalent bond)

29
Q

Why are chlorofluorocarbons dangerous

A

They continue to breakdown the ozone as the free radicals (which are very reactive), are regenerated

30
Q

Reaction with a CFC and ozone (include reaction summary and steps)

A
  1. Initiation
    2a. Propagation
    2b. Propagation
  2. Termination

Chemistry ER (4 decks)

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