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Questions and Answers
What does collision theory state regarding molecular interactions during a reaction?
What does collision theory state regarding molecular interactions during a reaction?
- Reactions can occur without any collisions.
- Only one molecule is necessary for a reaction to occur.
- A collision must be of specific energy to break bonds for a reaction. (correct)
- Higher concentrations of reactants inhibit collisions.
How does temperature affect the rate of reaction according to the principles of chemical kinetics?
How does temperature affect the rate of reaction according to the principles of chemical kinetics?
- Higher temperatures lead to more collisions and increased reaction rates. (correct)
- Increasing temperature decreases reaction rates.
- Temperature has no effect on reaction rates.
- Temperature only affects gaseous reactants.
What is the activation energy (Ea) in the context of chemical reactions?
What is the activation energy (Ea) in the context of chemical reactions?
- The energy that remains constant regardless of temperature.
- The energy released when products are formed.
- The energy required to stabilize reactants.
- The energy necessary to initiate a reaction by overcoming bond breaking. (correct)
According to the content, a 10°C increase in temperature typically results in what effect on decay or degradation rates?
According to the content, a 10°C increase in temperature typically results in what effect on decay or degradation rates?
What does the symbol $A$ represent in the Arrhenius equation?
What does the symbol $A$ represent in the Arrhenius equation?
In the equation log $k = log A - \frac{E_a}{2.303RT}$, what does $R$ denote?
In the equation log $k = log A - \frac{E_a}{2.303RT}$, what does $R$ denote?
What principle provides a better description of reaction rates than collision theory alone?
What principle provides a better description of reaction rates than collision theory alone?
What is the unit of the energy of activation $E_a$ in the Arrhenius equation?
What is the unit of the energy of activation $E_a$ in the Arrhenius equation?
If the temperature increases, how does it generally affect the reaction rate according to the Arrhenius equation?
If the temperature increases, how does it generally affect the reaction rate according to the Arrhenius equation?
What mathematically describes the relationship between the logarithm of the rate constant $k$ and temperature $T$ in the Arrhenius equation?
What mathematically describes the relationship between the logarithm of the rate constant $k$ and temperature $T$ in the Arrhenius equation?
What is the estimated shelf life of an antibiotic solution at room temperature (25°C) if it has a shelf life of 48 hours at 5°C and a Q10 value of 3?
What is the estimated shelf life of an antibiotic solution at room temperature (25°C) if it has a shelf life of 48 hours at 5°C and a Q10 value of 3?
If an ophthalmic solution has a shelf life of 6 hours at 25°C, how long would it last at 5°C given a Q10 value of 3?
If an ophthalmic solution has a shelf life of 6 hours at 25°C, how long would it last at 5°C given a Q10 value of 3?
Which of the following factors does NOT affect the reaction rate in chemical kinetics?
Which of the following factors does NOT affect the reaction rate in chemical kinetics?
For a chemical reaction, a Q10 value of 3 implies what kind of relationship between temperature and reaction rate?
For a chemical reaction, a Q10 value of 3 implies what kind of relationship between temperature and reaction rate?
How is the shelf life of a drug related to the temperature it is stored at, based on the Q10 principle?
How is the shelf life of a drug related to the temperature it is stored at, based on the Q10 principle?
What happens to the specific base-catalysis rate constant ($k_{obs}$) when the pH is low?
What happens to the specific base-catalysis rate constant ($k_{obs}$) when the pH is low?
Which equation correctly calculates the specific reaction rate constant at slightly alkaline pH?
Which equation correctly calculates the specific reaction rate constant at slightly alkaline pH?
What is the correct range for the pH of maximum stability for the reaction?
What is the correct range for the pH of maximum stability for the reaction?
How is ionic strength defined in the context of chemical kinetics?
How is ionic strength defined in the context of chemical kinetics?
Which of the following equations represents the relationship between the hydroxide concentration and the specific base-catalysis rate constant?
Which of the following equations represents the relationship between the hydroxide concentration and the specific base-catalysis rate constant?
Flashcards
Activation Energy (Ea)
Activation Energy (Ea)
The minimum energy required for molecules to react. Breaking bonds in reactants and forming new bonds in products requires energy.
Collision Theory
Collision Theory
A theory that explains how reactions occur based on collisions between molecules. To react, molecules must collide with enough energy to break existing bonds and form new ones. This is called activation energy.
Arrhenius Theory
Arrhenius Theory
A theory that shows how temperature affects reaction rate - The rate constant (k) increases exponentially with temperature. It predicts that the rate of chemical reactions increases as temperature increases.
Chemical Kinetics
Chemical Kinetics
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Reaction Rate
Reaction Rate
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Arrhenius Equation
Arrhenius Equation
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Arrhenius Factor (A)
Arrhenius Factor (A)
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Boltzmann Distribution
Boltzmann Distribution
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Gas Constant (R)
Gas Constant (R)
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Specific base-catalysis rate constant
Specific base-catalysis rate constant
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Specific acid-catalysis rate constant
Specific acid-catalysis rate constant
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Rate-pH profile
Rate-pH profile
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pH of maximum stability
pH of maximum stability
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Primary salt effect
Primary salt effect
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What is the Q10 value?
What is the Q10 value?
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What is shelf life?
What is shelf life?
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How can the Q10 value be used to predict shelf life?
How can the Q10 value be used to predict shelf life?
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What is the formula to calculate shelf life at a different temperature using Q10?
What is the formula to calculate shelf life at a different temperature using Q10?
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How does pH affect drug degradation?
How does pH affect drug degradation?
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Study Notes
Drug Stability and Chemical Kinetics: Temperature
- Chemical kinetics studies reaction rates
- Temperature significantly impacts reaction rates
- Collision theory states reactions occur via molecular collisions requiring minimum activation energy
- Reaction rates directly correlate with the number of collisions per unit time
- Increasing temperature increases collision frequency and reaction rate
- A 10°C rise generally results in a 2-5 fold increase in degradation rate
- Arrhenius theory provides more sophisticated descriptions of this relationship
Drug Stability and Chemical Kinetics: Arrhenius Equation
- Arrhenius equation expresses the relationship between reaction rate constant (k), temperature (T), and activation energy (Ea)
- The equation is in log form log k=log A -Ea/2.303R * T
- A is the frequency factor, reflecting reaction frequency, and influences the rate constant
- Ea represents the activation energy, which is required to initiate reactions and related to reaction processes
- R is the ideal gas constant, and its value is (1.98 cal/ mol k or 8.314 J/ mol k)
- Temperature (T) is measured in Kelvin; convert from Celsius using the formula: K = °C + 273
- The equation is useful for calculating activation energy (Ea) from rate constants at different temperatures
Drug Stability and Chemical Kinetics: Arrhenius Plot
- Arrhenius plot graphically depicts the relationship between the natural log of the rate constant (ln k) and the inverse of absolute temperature (1/T)
- The slope of the line in the plot is directly related to the activation energy (Ea)
- The y-intercept represents the frequency factor (A)
Drug Stability and Chemical Kinetics: Practice Problems (1)
- First order reactions are related to degradation reaction rates
- Degradation rates can be used to calculate activation energy (Ea)
- Calculating Ea using the provided reaction rates at different temperatures yields 25,574 cal/mol or 25.574 kcal/mol
Drug Stability and Chemical Kinetics: Practice Problems (2)
- Calculate the frequency factor (A) from rate constants and temperatures
- This method involves solving for A using the Arrhenius equation
Drug Stability and Chemical Kinetics: Applications
- Accelerated stability studies assess drug degradation rates under elevated temperatures, enabling the prediction of shelf life
- Q10 method estimates the effect of variable temperature changes on reaction rates, enabling a prediction of shelf-life
Drug Stability and Chemical Kinetics: Q10 Method
- Q10, or temperature coefficient, represents the factor by which a rate constant increases for a 10°C rise in temperature
- Q10 values relate to the activation energy (Ea)
- Q10 values are useful for estimations related to drug degradation rates at different temperatures
Drug Stability and Chemical Kinetics: Practice Problems (3)
- Find the estimated shelf life of a drug at a varying temperature given conditions
- For example, 48 hours in the refrigerator (5°C) can be used to determine the shelf life at a different temperature (25°C) given a specified Q10 value of 3.
Drug Stability and Chemical Kinetics: Practice Problems (4)
- Similar to problem (3), given a shelf life of a product at a specific temperature (room temperature), the expected shelf life at a different temperature (refrigerator temperature) can be determined.
Drug Stability and Chemical Kinetics: pH
- pH plays a significant role in drug stability (i.e., degradation of some drugs is influenced by acids/bases)
- Specific acid/base catalysis refers to reaction rates dependent on specific (i.e., "charged") acids/bases
- Reactions rates depend on the concentration of hydrogen or hydroxyl ions at low or high pH
- The specific acid-base catalysis involves reactions with an acid or base involved in a reaction, and the rates are dependent on the specific acid or base or the concentration
- Two general categories of catalysis include general acid/base catalysis and specific acid/base catalysis
- General acid/base catalysis is concerned with reactions involving a buffer system
- The rate constant (k) depends on the concentration of the specific hydrogen or hydroxyl ions, with higher rates observed at higher concentrations
Drug Stability and Chemical Kinetics: Examples of Specific Acid-Base Catalysis
- Illustrative examples of specific acid/base catalysis at low and high pH
- The rate of change in kobs is dependent on the specific concentration of either the hydrogen (H+) or hydroxyl (OH-) ions for specific acid/base catalysis conditions
Drug Stability and Chemical Kinetics: Determination of Rate-pH
- Calculation of the rate at a given pH to calculate the pH of maximum stability profiles, given the known pH dependence of drug degradation
Drug Stability and Chemical Kinetics: Medium Effect
- Ionic strength, the cumulative effect of charge from ions, influences drug stability
- Electrolytes (e.g., buffers or salts) altering the ionic strength affecting drug degradation rates.
Drug Stability and Chemical Kinetics: Ionic Strength Calculation
- The equation that describes how to calculate ionic strength (μ)
- The example shows applying the equation for determining ionic strength using appropriate components and concentration
Drug Stability and Chemical Kinetics: Brønsted-Bjerrum Equation
- This equation describes the influence of electrolytes on rate constants for ionic species interactions
- It details parameters such as rate constants (ko), constant (A), charge numbers (Za, Zb), and ionic strength (μ)
Drug Stability and Chemical Kinetics: Medium Effect (Continued /Examples)
- Similarly charged ions reacting
- E.g., acid-catalyzed hydrolysis in a cationic drug
- Oppositely charged ions reacting
- E.g., base-catalyzed hydrolysis in a cationic drug
Drug Stability and Chemical Kinetics: Oxygen and Light
- Oxygen availability can negatively impact drug stability in oxidation sensitive medicines
- Exposure to light can influence drug degradation
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Description
Explore the principles of drug stability and chemical kinetics, focusing on the effects of temperature on reaction rates. Understand the collision theory and the Arrhenius equation as key components that describe how temperature influences reaction dynamics and degradation rates.
