reaction kinetics Flashcards

1
Q

Why is chemical kinetics important in pharmacy + pharmacology?

A

1) determination of shelf-life of drugs

2) determination of amount of drug in body after a particular time period

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2
Q

What is chemical kinetics?

A

study of rate of reaction

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3
Q

reaction rate

A

concentration of reactants that disappear + products that form per unit time

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4
Q

What is the unit for reaction rate?

A

mol L⁻¹s⁻¹

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5
Q

instantaneous rate

A

rate at a particular time

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6
Q

collision theory

A

rate of a reaction is proportional to the number of effective collisions

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7
Q

effective collisions

A

collision that gives product molecules

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8
Q

How does concentration influence the number of effective collisions per second?

A

as the concentration of reactants increase, the number of effective collisions increases

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9
Q

Why do only a small number of collisions lead to a net change?

A

1) molecular orientation
2) activation energy
3) temperature

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10
Q

How does molecular orientation influence the number of effective collisions per second?

A

when two reactant molecules collide they must be oriented correctly for a reaction to occur

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11
Q

activation energy

A

minimum energy required for a reaction to occur

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12
Q

How does activation energy influence the number of effective collisions per second?

A

at a given temperature, only a certain fraction of collisions possess enough energy to be effective + form products

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13
Q

How does temperature influence the number of effective collisions per second?

A

as temperature increases, the rate of a reaction increases

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14
Q

Arrhenius equation

A

k = Ae⁻ᴱₐ/ᴿᵀ

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15
Q

k =

A

1) rate constant

2) Ae⁻ᴱₐ/ᴿᵀ

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16
Q

Eₐ

A

activation energy

17
Q

R

A

universal gas constant, 8.314 J mol⁻¹ K⁻¹

18
Q

T

A

temperature, K

19
Q

A

A

pre-exponential/frequency factor

20
Q

ln k₂/k₁ =

A

-Eₐ/R (1/T₂ - 1/T₁)

21
Q

temperature coefficient, Q₁₀

A

1) measure of how the rate of reaction changes for every 10°C change in temperature
2) 2-3

22
Q

t₁₀%

A

shelf-life

23
Q

shelf-life

A

time taken for 10% of a drug to decompose at 25°C

24
Q

t₁₀% (T₂) =

A

t₁₀% (T₁) / Q₁₀Δᵀ/¹⁰

25
rate determining step
slowest step
26
How do most active pharmaceutical ingredients (APIs) decompose?
1) hydrolysis 2) oxidation 3) photochemical decomposition 4) polymerisation 5) isomerisation
27
What is hydrolysis?
reaction of a chemical with water
28
How is hydrolysis catalysed?
presence of acid/base
29
How can hydrolysis be reduced?
1) reducing storage temperature 2) processing API in solid state 3) store in dry conditions 4) controlling pH
30
What is oxidation a major cause of?
instability in dosage forms
31
How can oxidation be initiated?
presence of free radicals formed from exposure to light/heat
32
Is oxidation fast or slow?
slow
33
How can oxidation be reduced?
1) storage in amber bottles 2) storing heat-sensitives at low temperatures 3) removing trace metals from tablet pressing 4) antioxidants
34
What is photochemical decomposition?
decomposition initiated by light
35
How does photochemical decomposition proceed?
via a free-radical mechanism
36
How can photochemical decomposition be reduced?
1) keep away from light 1) coating tablet with suitable polymer 3) storage in dark/amber bottles
37
What is isomerisation?
process where an API may be converted into its different isomers
38
How can isomerisation be reduced?
controlling pH