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Questions and Answers
In a zero-order reaction, how is the rate of reaction affected by changes in the concentration of the reactant?
In a zero-order reaction, how is the rate of reaction affected by changes in the concentration of the reactant?
- The rate increases proportionally with concentration.
- The rate remains constant regardless of concentration. (correct)
- The rate decreases as concentration increases.
- The rate only changes at specific concentration thresholds.
What is the molecularity of a reaction step that involves one molecule breaking into two ions?
What is the molecularity of a reaction step that involves one molecule breaking into two ions?
- Three molecularity
- Two molecularity
- Zero molecularity
- One molecularity (correct)
Which of the following is true about a bimolecular reaction?
Which of the following is true about a bimolecular reaction?
- It involves two reacting species. (correct)
- It has a molecularity of zero.
- It can only occur in one step.
- It involves three or more species.
The integrated rate law for a first-order reaction can be expressed in which format?
The integrated rate law for a first-order reaction can be expressed in which format?
What is the significance of integrating the rate law in chemical kinetics?
What is the significance of integrating the rate law in chemical kinetics?
What is the half-life of a first-order reaction if the rate constant (k) is $8.8 \times 10^{-3} \text{ day}^{-1}$?
What is the half-life of a first-order reaction if the rate constant (k) is $8.8 \times 10^{-3} \text{ day}^{-1}$?
Which of the following is a characteristic of first-order reactions?
Which of the following is a characteristic of first-order reactions?
Which scenario describes a second-order reaction?
Which scenario describes a second-order reaction?
For a reaction that has a rate constant of $k = 0.1 \text{ M}^{-1}\text{s}^{-1}$ and involves two reactants, what type of reaction is it?
For a reaction that has a rate constant of $k = 0.1 \text{ M}^{-1}\text{s}^{-1}$ and involves two reactants, what type of reaction is it?
In a zero-order reaction, which of the following statements is true?
In a zero-order reaction, which of the following statements is true?
What is the rate expression for the hydrolysis of ethyl acetate considered to be when both reactants are present, but one is in large excess?
What is the rate expression for the hydrolysis of ethyl acetate considered to be when both reactants are present, but one is in large excess?
Which of the following best describes a pseudo-zero order reaction?
Which of the following best describes a pseudo-zero order reaction?
If the reaction order is determined to be second order in a simple reaction, what would be the impact on the rate if the concentration of the reactant is doubled?
If the reaction order is determined to be second order in a simple reaction, what would be the impact on the rate if the concentration of the reactant is doubled?
When determining reaction order using the substitution method, what is primarily kept constant?
When determining reaction order using the substitution method, what is primarily kept constant?
What is the half-life expression for a second order reaction with respect to its initial concentration?
What is the half-life expression for a second order reaction with respect to its initial concentration?
Which condition is necessary for a reaction to be classified as pseudo-first order?
Which condition is necessary for a reaction to be classified as pseudo-first order?
In a reaction that switches from pseudo-zero order to first order, what usually causes this transition?
In a reaction that switches from pseudo-zero order to first order, what usually causes this transition?
Why would the hydrolysis of ethyl acetate be categorized as a second order reaction despite being treated as first order in a dilute solution?
Why would the hydrolysis of ethyl acetate be categorized as a second order reaction despite being treated as first order in a dilute solution?
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Study Notes
Shelf-life of a First-order Reaction
- The shelf-life of a first-order reaction is given by the formula: t = ln(1.11) / k
- The shelf-life of a first-order reaction is the time it takes for the concentration of the reactant to decrease to 90% of its original value.
Examples of First-Order Reactions
- Decomposition of hydrogen peroxide
- Decomposition of cyclopropane to propene
- Decomposition of nitrous pentaoxide
- Passive diffusion of drugs through biological membranes
- Processes of drug absorption, distribution, metabolism and excretion
- Rate of growth of microorganisms
- Rate of killing of microorganisms by heat or chemical agents
Second Order Reaction
- A reaction is said to be a second order reaction if the rate of reaction is proportional to the concentration of each of two reactants or the second power of the concentration of one reactant.
- For example, a reaction involving a single molecule breaking into ions has a molecularity of 1 and can be described as unimolecular.
- Another example is a reaction involving two ions reacting together, which has a molecularity of 2 and is considered a bimolecular reaction.
Integrated Rate Law
- This expression relates the concentration of reactants to the time of the reaction.
- It is derived from the rate law by integration.
Zero Order Reaction
- The rate is independent of the concentration of the reactant.
Pseudo-Order Reactions
- Pseudo-Zero Order: The rate of reaction in a suspension is pseudo-zero order because there is an excess of the drug in the suspension, acting as a reservoir. This means that the concentration of the reactant appears constant, as the reservoir compensates for the concentration being used up.
- Pseudo-First Order: A chemical reaction obeys pseudo-first-order kinetics when the rate of the process is proportional to the concentration of only one reactant, even though the reaction involves several reactants. An example is the hydrolysis of ethyl acetate, where the concentration of water is much higher than that of ethyl acetate and is essentially constant. This makes the reaction appear first-order, with a modified rate constant.
Determination of Reaction Order
- Substitution Method: This method involves substituting the data obtained from a kinetic experiment into the relevant integrated rate equation. The equation where the k values remain constant determines the order of the reaction.
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