reaction kinetics

Question 1

Why is chemical kinetics important in pharmacy + pharmacology?

Answer 1

1) determination of shelf-life of drugs

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

Question 2

What is chemical kinetics?

Answer 2

study of rate of reaction

Question 3

reaction rate

Answer 3

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

Question 4

What is the unit for reaction rate?

Answer 4

mol L⁻¹s⁻¹

Question 5

instantaneous rate

Answer 5

rate at a particular time

Question 6

collision theory

Answer 6

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

Question 7

effective collisions

Answer 7

collision that gives product molecules

Question 8

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

Answer 8

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

Question 9

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

Answer 9

1) molecular orientation
2) activation energy
3) temperature

Question 10

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

Answer 10

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

Question 11

activation energy

Answer 11

minimum energy required for a reaction to occur

Question 12

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

Answer 12

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

Question 13

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

Answer 13

as temperature increases, the rate of a reaction increases

Question 14

Arrhenius equation

Answer 14

k = Ae⁻ᴱₐ/ᴿᵀ

Question 15

k =

Answer 15

1) rate constant

2) Ae⁻ᴱₐ/ᴿᵀ

Question 16

Eₐ

Answer 16

activation energy

Question 17

R

Answer 17

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

Question 18

T

Answer 18

temperature, K

Question 19

A

Answer 19

pre-exponential/frequency factor

Question 20

ln k₂/k₁ =

Answer 20

-Eₐ/R (1/T₂ - 1/T₁)

Question 21

temperature coefficient, Q₁₀

Answer 21

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

Question 22

t₁₀%

Answer 22

shelf-life

Question 23

shelf-life

Answer 23

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

Question 24

t₁₀% (T₂) =

Answer 24

t₁₀% (T₁) / Q₁₀Δᵀ/¹⁰

Question 25

rate determining step

Answer 25

slowest step

Question 26

How do most active pharmaceutical ingredients (APIs) decompose?

Answer 26

1) hydrolysis
2) oxidation
3) photochemical decomposition
4) polymerisation
5) isomerisation

Question 27

What is hydrolysis?

Answer 27

reaction of a chemical with water

Question 28

How is hydrolysis catalysed?

Answer 28

presence of acid/base

Question 29

How can hydrolysis be reduced?

Answer 29

1) reducing storage temperature
2) processing API in solid state
3) store in dry conditions
4) controlling pH

Question 30

What is oxidation a major cause of?

Answer 30

instability in dosage forms

Question 31

How can oxidation be initiated?

Answer 31

presence of free radicals formed from exposure to light/heat

Question 32

Is oxidation fast or slow?

Answer 32

slow

Question 33

How can oxidation be reduced?

Answer 33

1) storage in amber bottles
2) storing heat-sensitives at low temperatures
3) removing trace metals from tablet pressing
4) antioxidants

Question 34

What is photochemical decomposition?

Answer 34

decomposition initiated by light

Question 35

How does photochemical decomposition proceed?

Answer 35

via a free-radical mechanism

Question 36

How can photochemical decomposition be reduced?

Answer 36

1) keep away from light
1) coating tablet with suitable polymer
3) storage in dark/amber bottles

Question 37

What is isomerisation?

Answer 37

process where an API may be converted into its different isomers

Question 38

How can isomerisation be reduced?

Answer 38

controlling pH