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The reaction 3A + 2B → 2C + 3D has a rate law of Rate = k[A]3.
False
If the concentration of B is doubled and the rate does not change, the reaction is first order with respect to [B].
False
A doubling of the concentration of A results in a quadrupling of the reaction rate, indicating that the reaction is second order with respect to [A].
True
In zero order kinetics, the concentration of reactant decreases at a constant rate until all reactant is consumed.
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The equation [A] − [A]o = −kt is applicable for first-order reactions.
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A plot of [A] versus time for a zero-order reaction will yield a straight line.
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The rate law for the reaction A + B → C can be expressed as Rate = k[A][B].
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In zero order kinetics, the reaction rate decreases abruptly to zero when the reactant is fully consumed.
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For zero order kinetics, the plot of concentration vs time will yield a straight line if the slope is equal to −k.
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The equation ln [A] = -kt + ln [A]0 describes the integrated rate law for second order kinetics.
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The half-life of a first order reaction is directly dependent on the initial concentration of the reactant.
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Doubling the concentration of reactant A will lead to a doubling of the reaction rate in first order kinetics.
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In second order kinetics, the plot of 1/[A] vs time should yield a straight line with a slope of k.
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Activation energy is defined as the energy required for molecules to collide and form products.
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Increasing the temperature generally decreases the rate of a chemical reaction.
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The orientation factor in the collision model suggests that the arrangement of molecules must be correct for a successful reaction.
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For zero order reactions, the half-life can be calculated using the formula t1/2 = [A]0 / 2k.
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The Arrhenius equation shows a direct, linear relationship between temperature and reaction rate.
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The activation energy, Ea, is represented as a positive value in the Arrhenius Equation.
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The slope of the graph of lnk versus 1/T is represented by the equation -Ea/R.
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A rate coefficient, k, can be evaluated at two different temperatures to determine the activation energy for a reaction.
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Increasing the frequency factor, A, will result in a slower reaction rate according to the Arrhenius equation.
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In a multi-step reaction, the slowest step is termed the rate determining step.
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The fraction of molecules possessing the activation energy is irrelevant to the overall reaction rate.
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Collisions between reactant molecules must have both the correct energy and orientation to result in a reaction.
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Pharmaceutical stability evaluations are influenced by the activation energy and rates of degradation.
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A higher activation energy results in a faster reaction rate.
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For a two-step reaction with an intermediate, the rate of reaction is determined solely by the second step.
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The rate coefficient for the decomposition of sucrose is determined from the second order kinetics.
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The decomposition of penicillin at higher temperatures results in a higher rate coefficient.
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The half-life of a first-order reaction depends on the initial concentration of the reactant.
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The Arrhenius equation calculates the activation energy of a reaction using the temperature in Kelvin.
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At 23°C, a concentration of 0.316 M of sucrose indicates it is at its maximum stability in 0.5M HCl solution.
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The step converting A to B is the slow step when $k_1 \ll k_2$.
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B is consumed at the same rate it is produced under the steady state approximation.
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The concentration of B can always be directly observed in a reaction.
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For a first order reaction, the integrated form of the rate law includes a logarithmic relation with the initial concentration.
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In second order kinetics, the half-life formula does not depend on the initial concentration.
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If $k_1 \gg k_2$, the rate of the reaction can be simplified to $k_1 A$.
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In a zero order reaction, the concentration of A decreases linearly over time.
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The steady state approximation can be applied only if $k_1$ is significantly less than $k_2$.
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The half-life for zero order reactions increases as the initial concentration of A decreases.
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The reaction rate is independent of concentration in a zero order reaction.
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Study Notes
Reaction Rates
- The rate law for a reaction describes the overall rate of the reaction.
- Rate laws are typically experimentally determined.
- Reaction order is an index of how the concentration of each reactant affects the rate of the reaction.
- Order of reaction can be determined by the initial rates method:
- Varying the concentration of one reactant at a time, while keeping the other reactants constant.
- Compare the initial reaction rates.
- Zero order reactions
- The rate of the reaction is independent of reactant concentration.
- The reactant concentration falls at a constant rate until all reactants are used up.
- The rate constant has units of concentration per time.
- The half-life is dependent on the initial concentration.
- First order reactions
- The rate of the reaction is directly proportional to the reactant concentration.
- Doubling the reactant concentration doubles the rate of reaction.
- The rate constant has units of 1/time.
- The half-life is independent of the initial concentration and is given by ln2/k.
- Second order reactions
- The rate of the reaction is proportional to the square of the reactant concentration.
- Doubling the reactant concentration quadruples the rate of reaction.
- The rate constant has units of 1/(concentration*time).
- The half-life is dependent on the initial concentration and is given by 1/(k*[A]0)
Temperature and Rate
- The rate of most chemical reactions increases as temperature increases.
- The rate coefficient (k) increases with temperature.
- This increase in rate is explained by the collision model.
- Collision Model:
- For a reaction to occur, molecules must collide with sufficient energy and with appropriate orientation.
- Only a small fraction of collisions will lead to reaction.
- Increasing temperature increases the number of collisions and the proportion of molecules with sufficient energy to react.
Activation Energy
- The minimum energy required for a reaction to occur is called the Activation Energy (Ea).
- Every reaction has a different activation energy.
- The value of Ea can be obtained from the Arrhenius equation:
- k = Ae-Ea/RT
- k is the rate coefficient
- Ea is the activation energy
- R is the gas constant
- T is the temperature
- A is the frequency factor (related to the frequency of collisions and the probability that the collisions are favorably oriented for the reaction)
Multi-Step Reactions
- Many pharmaceutical reactions involve multiple steps, each with its own activation energy and rate coefficient.
- The rate determining step is the slowest step in the reaction.
- If k1 << k2, then the first step is the rate determining step.
Steady State Approximation
- The steady-state approximation is used to simplify the analysis of complex reactions involving multiple steps.
- It assumes that the concentration of intermediate products is low and relatively constant during the reaction because it is being formed and consumed at roughly the same rate.
- This allows the rate of the reaction to be expressed in terms of the concentrations of observable reactants.
Applications in Pharmaceutical Sciences
- Understanding reaction rates and activation energies is essential for predicting the stability of pharmaceutical products.
- These parameters help to determine the shelf life of drugs and can inform decisions about storage conditions.
- Knowledge of reaction rates can also be used to optimize manufacturing processes and to design new drugs with desired properties.
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Description
Explore the concepts of reaction rates and rate laws in chemical kinetics. This quiz covers the determination of reaction order, characteristics of zero and first order reactions, and the methods used to analyze reaction rates. Test your understanding of how reactant concentrations influence reaction dynamics.
