38 Questions
What is the order of reaction if a plot of 1/(a – x)2 against t produces a straight line with all reactants at the same initial concentration?
Third order
What is the relation between half-life and initial concentration in a zero order reaction?
Half-life is proportional to initial concentration
What is the effect of a 10K rise in temperature on the rate constant?
It increases the rate constant by 2 or 3 folds
What is the unit of R in the Arrhenius equation?
Calorie/degree.Mole
What is the equation that governs the general effect of temperature on reaction kinetics?
K = Ae^(-Ea/RT)
What is the effect of light on the rate of reaction?
It increases the rate of reaction
What is the method called when a reaction is carried out at different temperatures?
Temperature variation method
What is the relation between half-life and initial concentration in a second order reaction?
Half-life is inversely proportional to initial concentration
What is the main objective of Accelerated Stability Studies?
To determine the expiration date of a drug
How is the rate constant evaluated in Accelerated Stability Studies?
By plotting the stability data at multiple temperatures
What is the purpose of plotting the logarithm of k against reciprocal absolute temperature?
To determine the activation energy Ea
What is the typical range of activation energy Ea values?
50-96 KJmol-1
What is the ultimate goal of Accelerated Stability Studies?
To predict the shelf-life of a drug
What is the advantage of using Accelerated Stability Studies?
It predicts the shelf-life of a drug under storage conditions
What is the equation that relates the logarithm of rate constants at two different temperatures?
Log K1 - Log K2 = Ea / 2.303R(T1 - T2)
What is the effect of increasing the polarity of the solvent on the reaction rate?
The reaction rate increases
What is the relationship between the specific rate constant and ionic strength?
The specific rate constant is directly proportional to the ionic strength
What is the dielectric constant related to in a solvent?
Ability to separate reactants
What is the unit of activation energy?
Joules per mole
What is the effect of increasing the temperature on the rate constant?
The rate constant increases
What is the equation that relates the logarithm of rate constants at infinite ionic strength?
Log K = Log Ko + 1.02ZAZBõ
What is the effect of a reaction involving a neutral molecule on the ionic strength?
The rate constant is independent of the ionic strength
What is the characteristic of zero-order kinetics?
Concentration of the reactant remains constant
What is the shelf-life of a drug product?
The time period during which a drug product is expected to remain within the approved specification
What is the order of reaction in the equation Rate = k[A]a[B]b, where a + b = 1?
First order
What happens to the suspended particles in a suspension as the drug decomposes in solution?
More drug is released from them
What is the expiration date of a drug product?
The date before which the product is expected to remain within the approved shelf-life specification
What is the characteristic of a first-order reaction?
The rate of reaction is proportional to the concentration of the reactant
What is the time required for 10% of the material to disappear?
Shelf-life
What happens to the system after all the suspended particles have been converted into drug in solution?
The system changes to a first-order reaction
What is the minimum time period covered by data for a long-term study at 25°C ± 2°C/60% RH ± 5% RH?
12 months
At what temperature and relative humidity is an intermediate study typically conducted?
30°C ± 2°C/65% RH ± 5% RH
What is the minimum time period covered by data for an accelerated study at 40°C ± 2°C/75% RH ± 5% RH?
6 months
At what temperature is a long-term study typically conducted for active pharmaceutical ingredients intended for storage in a refrigerator?
5°C ± 3°C
What is the minimum time period covered by data for a long-term study at -20°C ± 5°C?
12 months
What is the key application of reaction kinetics mentioned in the text?
Transport processes of drugs in the body
What is the rate of breakdown of Benzocaine at 30°C?
1.6 x 10^-7 sec^-1
What is the criterion for a drug to be considered ineffective?
After 70% decomposition
Study Notes
Zero-Order Kinetics
- The velocity of fading is constant and independent of the concentration of the color used.
- Suspensions are a case of zero-order kinetics, where the concentration in solution depends on the drug's solubility.
- The concentration remains constant as the drug decomposes in solution, and more drug is released from the suspended particles.
Shelf-Life
- Shelf-life is the time required for 10% of the material to disappear, or the time at which a material has decreased to 90% of its original concentration.
- It is the time period during which a drug product is expected to remain within the approved specification for use, provided that it is stored under the conditions defined on the container label.
First-Order Reactions
- The rate of a reaction is proportional to the 1st power of concentration of a reactant and may be expressed mathematically as Rate = k[A]a[B]b.
- The order of reaction is a + b = 1.
- The rate of reaction is dependent on only one of the reactants.
Half-Life Method
- In a zero-order reaction, the half-life is proportional to the initial concentration, a.
- The half-life of a 1st order reaction is independent of a.
- ti/2 for a second-order reaction, in which a=b, is proportional to 1/a.
- In a third-order reaction, in which a=b=c, it is proportional to 1/a2.
Factors Affecting the Rate of Reactions
- Temperature: an increase in temperature increases the rate of reaction.
- A 10K rise in temperature increases the rate constant 2 or 3 folds.
- The general effect of temperature is governed by Arrhenius Equation (1889).
Arrhenius Equation
- K = Ae-Ea/RT, where K is the specific reaction rate, Ea is the activation energy, A is the frequency factor, R is the gas constant, and T is the absolute temperature.
- The equation can be modified to LogK = LogA - Ea/2.303RT.
Solvents
- Three properties of solvents that can influence the reaction rate:
- Polarity: a more polar solvent can favour the reaction.
- Ionic strength: the specific rate constant is directly proportional to the ionic strength.
- Dielectric constant: the ability of the solvent to separate the reactant and product.
Accelerated Stability Studies
- A method to predict chemical stability of a formulation during pre-formulation studies.
- The study involves determining the order of reaction from the plotting of stability data at several elevated temperatures.
WHO Stability Information
- Study conditions and minimum time periods covered by data at submission to regulatory bodies:
- Long-term: 25°C ± 2°C/60% RH ± 5% RH, 12 months.
- Intermediate: 30°C ± 2°C/65% RH ± 5% RH, 6 months.
- Accelerated: 40°C ± 2°C/75% RH ± 5% RH, 6 months.
Application of Reaction Kinetics
- Transport process of drug in the body, including absorption, distribution, and elimination.
- Pharmaceutical sciences, such as physical pharmacy and pharmaceutical sciences.
This quiz covers zero-order kinetics in suspensions, including the concept of constant velocity of fading and apparent zero-order kinetics.
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