Ib Chemistry Hl Topic 16

1. Distinguish between the terms rate constant, overall order of reaction and order of reaction with respect to a particular reactant.

Rate expression: The rate constant is the sum of the orders of the individual reactants. Order of reaction: The rate expression shows the proportionality between the reaction rate and the concentrations of the products.

Rate expression: The order of reaction is as follows: m + n = overall order Rate constant: The constant represents the concentration of the reactants multiplied by the rate of the reaction.

Rate expression: The concentrations of the reactants to the power of the order of each productmultiplied by the rate constant: Rate=k[A]m[B]n[C]o Order of reaction: The order of reaction is said to be m for substance A, n for substance B, etc. Thetotal order of reaction is the sum of these powers, ie m + n etc = overall order Rate constant: The constant in the above equation represents the proportionality between the reactionrate and the concentrations of the reactants. Its units depend on the number of reactants and theirorders.

Order of reaction: The overall order of reaction is the proportionality constant between the concentration of the reactants and the rate of the reaction. Rate constant: The total order is the sum of the powers of the concentration terms.

2. Deduce the rate expression for a reaction from experimental data.

The rate equation only depends on the final products formed in a reaction, not the concentrations of the reactants.

It is an experimentally determined equation in that the information (n,m,k etc) can only be found through experimentation and not through theoretical considerations. The rate equation shows the relationship between the speed of a reaction and the concentrations of the individual reactants. Once the orders are found then they provide information regarding the mechanism of the specific reaction.

The rate expression for a reaction can be accurately predicted based solely on theoretical considerations without the need for experimentation.

The orders in a rate equation are determined based on the physical state of the reactants rather than their concentrations.

Experimental data is crucial in determining the rate expression for a reaction as theoretical predictions alone are not sufficient. The rate equation specifically relates the reaction speed to the concentrations of reactants, allowing for insights into the reaction mechanism.

Explanation

Experimental data is crucial in determining the rate expression for a reaction as theoretical predictions alone are not sufficient. The rate equation specifically relates the reaction speed to the concentrations of reactants, allowing for insights into the reaction mechanism.

3. Explain the concept that reactions can occur by more than one step and that the slowest step determines the rate of reaction (rate-determining step).

Catalyst: A substance that increases the rate of a reaction without being consumed.

Equilibrium constant: The ratio of products to reactants at equilibrium.

Activation energy: The energy needed for a reaction to occur.

Rate determining step: The slowest step in the sequence of steps leading to the formation of products. Molecularity: The number of molecules reacting in an elementary step.

4. Describe the relationship between reaction mechanism, order of reaction and rate-determining step.

The rate-determining step is always the first step in a multi-step reaction.

Mechanism is only relevant for single-step reactions and does not affect the overall reaction rate.

Order of reaction is determined solely by the concentration of reactants and does not relate to the reaction mechanism.

Only examples with one- or two-step reactionswhere the mechanism is given will be assessed.
In summary, a mechanism is a model of how a reactionoccurs. The rate of overall reaction is the rate of the sloweststep. This slowest step is called the rate determining step.Species produced in earlier steps of the mechanism thatare consumed in later steps are called intermediates. Amechanism must account for the overall stoichiometryof the reaction, the observed rate expression and anyother available evidence (such as the effect of light or acatalyst).

The correct answer highlights the importance of considering the entire mechanism in determining the rate-determining step and overall reaction rate, rather than being limited to specific scenarios. The incorrect answers provide common misconceptions that are contradicted by the relationship between reaction mechanism, order of reaction, and rate-determining step.

Explanation

The correct answer highlights the importance of considering the entire mechanism in determining the rate-determining step and overall reaction rate, rather than being limited to specific scenarios. The incorrect answers provide common misconceptions that are contradicted by the relationship between reaction mechanism, order of reaction, and rate-determining step.

5. Determine activation energy (Ea) values from the Arrhenius equation by a graphical method.

Conducting experiments at different temperatures to directly measure the activation energy.

Applying the principles of quantum mechanics to calculate the activation energy.

The Arrhenius equation and its logarithmic form areprovided in the Chemistry data booklet. The use ofsimultaneous equations will not be assessed.

Using trial and error methods to guess the activation energy value.

The correct method to determine activation energy (Ea) values from the Arrhenius equation is by utilizing the provided equation and its logarithmic form. This method does not involve conducting experiments at different temperatures or applying quantum mechanics principles. Guessing or using trial and error methods is not a reliable approach for determining activation energy.

Explanation

The correct method to determine activation energy (Ea) values from the Arrhenius equation is by utilizing the provided equation and its logarithmic form. This method does not involve conducting experiments at different temperatures or applying quantum mechanics principles. Guessing or using trial and error methods is not a reliable approach for determining activation energy.