Chemistry: First and Second Order Reactions

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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?

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?

Three molecularity

Two molecularity

Zero molecularity

One molecularity (correct)

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?

ln[A] = -kt + ln[A]₀ Signup and view all the answers

What is the significance of integrating the rate law in chemical kinetics?

It relates concentration of reactants to the reaction time. Signup and view all the answers

What is the half-life of a first-order reaction if the rate constant (k) is $8.8 \times 10^{-3} \text{ day}^{-1}$?

78 days Signup and view all the answers

Which of the following is a characteristic of first-order reactions?

Rate depends on the concentration of one reactant Signup and view all the answers

Which scenario describes a second-order reaction?

Reaction involving two different reactants at the same concentration Signup and view all the answers

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?

Second-order reaction Signup and view all the answers

In a zero-order reaction, which of the following statements is true?

The rate remains constant regardless of the concentration of reactants. Signup and view all the answers

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?

Rate = k [CH3COOC2H5] Signup and view all the answers

Which of the following best describes a pseudo-zero order reaction?

The concentration of the reactant remains constant over the reaction time. Signup and view all the answers

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?

The rate will quadruple. Signup and view all the answers

When determining reaction order using the substitution method, what is primarily kept constant?

Rate constant k Signup and view all the answers

What is the half-life expression for a second order reaction with respect to its initial concentration?

$t_{1/2} = 1/(k[C_0])$ Signup and view all the answers

Which condition is necessary for a reaction to be classified as pseudo-first order?

One reactant must be present in negligible concentration. Signup and view all the answers

In a reaction that switches from pseudo-zero order to first order, what usually causes this transition?

The reactant becomes entirely consumed. Signup and view all the answers

Why would the hydrolysis of ethyl acetate be categorized as a second order reaction despite being treated as first order in a dilute solution?

One reactant is in significant excess. Signup and view all the answers

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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Description

Explore the concepts of first-order and second-order reactions in this quiz. Learn about the shelf-life of first-order reactions, examples, and the nuances of second-order reactions, including their rate laws and applications. Test your understanding of important chemical kinetics principles.