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What is the primary focus of reaction kinetics?
What is the primary focus of reaction kinetics?
The rate of a reaction is influenced solely by the concentration of reactants.
The rate of a reaction is influenced solely by the concentration of reactants.
False
What is the significance of determining the half-life of a reaction?
What is the significance of determining the half-life of a reaction?
It helps in understanding the time required for the concentration of a reactant to reduce to half its initial value.
The term _____ refers to the concentration of reactants raised to the power equal to the number of molecules undergoing reaction.
The term _____ refers to the concentration of reactants raised to the power equal to the number of molecules undergoing reaction.
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Match the following terms with their definitions:
Match the following terms with their definitions:
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Which of the following factors is NOT typically considered when studying reaction kinetics?
Which of the following factors is NOT typically considered when studying reaction kinetics?
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The order of a reaction can be determined by summing the exponents of the reactants' concentrations.
The order of a reaction can be determined by summing the exponents of the reactants' concentrations.
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What does the symbol 'K' denote in reaction kinetics?
What does the symbol 'K' denote in reaction kinetics?
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To advise a patient on the proper _____ conditions for drug storage, knowing the kinetics is essential.
To advise a patient on the proper _____ conditions for drug storage, knowing the kinetics is essential.
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In a zero-order reaction, what is the relationship between reactant concentration and the rate of reaction?
In a zero-order reaction, what is the relationship between reactant concentration and the rate of reaction?
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What does the half-life of a zero-order reaction represent?
What does the half-life of a zero-order reaction represent?
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The shelf life of a zero-order reaction is the time required for 50% of the material to disappear.
The shelf life of a zero-order reaction is the time required for 50% of the material to disappear.
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What is the formula for the shelf life of a zero-order reaction?
What is the formula for the shelf life of a zero-order reaction?
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In apparent or pseudo-order reactions, one of the reactants is present in ________ excess.
In apparent or pseudo-order reactions, one of the reactants is present in ________ excess.
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In zero-order kinetics, what remains constant over time?
In zero-order kinetics, what remains constant over time?
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What type of reaction does a second-order reaction behave like when the concentration of water is constant?
What type of reaction does a second-order reaction behave like when the concentration of water is constant?
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In first-order reactions, the half-life is dependent on the concentration of the reactant.
In first-order reactions, the half-life is dependent on the concentration of the reactant.
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The graphical method determines reaction order by plotting the concentration against time.
The graphical method determines reaction order by plotting the concentration against time.
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What characterizes the rate of a first-order reaction?
What characterizes the rate of a first-order reaction?
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What is the importance of the half-life method in determining reaction order?
What is the importance of the half-life method in determining reaction order?
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In a zero-order reaction, the half-life can be expressed as ________ = C0 / (2K).
In a zero-order reaction, the half-life can be expressed as ________ = C0 / (2K).
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The half-life of a reaction is defined as the time taken for ______ of the reactant to decompose.
The half-life of a reaction is defined as the time taken for ______ of the reactant to decompose.
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What happens to the concentration in a suspension under apparent zero-order kinetics?
What happens to the concentration in a suspension under apparent zero-order kinetics?
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Match the methods for determining reaction order with their descriptions:
Match the methods for determining reaction order with their descriptions:
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Which integrated equation indicates a first-order reaction when plotted as log concentration versus time?
Which integrated equation indicates a first-order reaction when plotted as log concentration versus time?
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The Arrhenius equation shows that reaction rate is unrelated to temperature.
The Arrhenius equation shows that reaction rate is unrelated to temperature.
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What is the activation energy for the hydrolysis of sulfacetamide at 120°C?
What is the activation energy for the hydrolysis of sulfacetamide at 120°C?
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According to the half-life method, the half-lives at initial concentrations a1 and a2 are denoted as ______ and ______.
According to the half-life method, the half-lives at initial concentrations a1 and a2 are denoted as ______ and ______.
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What does the substitution method rely on to determine the order of a reaction?
What does the substitution method rely on to determine the order of a reaction?
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Study Notes
Lecture 9: Kinetics, Reaction Rates, and Drug Stability
- This lecture covers reaction kinetics, the study of the rate of chemical change and how external factors affect it.
- Kinetics is derived from "kinesis," the Greek word for movement, emphasizing the dynamic nature of reactions.
- Reaction rates depend on reactant concentrations, products, other chemical species in the environment, solvent properties, pressure, and temperature.
- Understanding kinetics is important in determining drug stability.
Importance of Studying Kinetics
- Determining half-life (t1/2): the time needed for half of the drug to decompose.
- Determining shelf-life (t90): the time needed for 10% of the drug to decompose.
- Proper storage conditions selection.
- Incompatibility identification.
- Dissolution determination (the rate at which a substance dissolves).
- ADME Processes study in pharmacokinetics (absorption, distribution, metabolism, and excretion).
Rate and Order of Reactions
- Rate of reaction: the speed or velocity of a chemical reaction. Measured by conc. changes over time (rate = ±dc/dt).
- Order of reaction: how reactant concentration influences reaction speed.
- Reaction rate is proportional to reactant concentration raised to powers equal to their respective stoichiometric coefficients. (Rate = k [A]a [B]b)
- Order of reaction is the sum of exponents of the concentration terms in the rate law.
Zero-Order Reactions
- Reaction rate is independent of reactant concentration.
- Rate is constant over time.
- Rate = -dc/dt = k [A]º = k.
- Concentration decreases linearly with time (C = C0 - kt).
- Half-life (t1/2) = C0 / 2k, where C0 is the initial concentration.
- Shelf-life is calculated by setting C = 0.9 C0 and solving for t.
First-Order Reactions
- Reaction rate directly proportional to the first power of a single reactant's concentration.
- Rate = -dc/dt = kC
- Concentration decreases exponentially over time (C = C0e-kt).
- Half-life (t1/2) = 0.693/k.
- Shelf-life calculation involves setting C = 0.9C0 and solving for t
Apparent or Pseudo-First-Order Kinetics
- Involves reactions where one reactant is in large excess, behaving as a pseudo-constant.
- The reaction follows first-order kinetics despite being a second- or a higher-order reaction.
- Related to drug hydrolysis and drug decomposition in solution
Methods for Determining Reaction Order
- Substitution method: Substituting experimental data into integrated equations to determine a consistent K.
- Graphical method: Plotting relevant data (e.g., concentration vs. time for zero-order) to analyze reaction behavior.
- Half-life method: Comparing half-lives to determine the reaction order using different initial concentrations.
Factors Affecting Drug Stability
-
Temperature:
- Higher temperatures generally increase reaction rates following the Arrhenius equation (k = Ae-Ea/RT).
- The speed of many reactions approximately doubles or triples with every 10°C rise in temperature.
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Description
This quiz focuses on the essential concepts of kinetics, including reaction rates and their relevance to drug stability. Students will explore factors such as concentration, temperature, and pressure that influence these reaction rates. Understanding half-life and shelf-life of drugs is critical for effective pharmacological practices.
