Catalysis and Reaction Rates

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Questions and Answers

In the catalytic formation of $SO_3$ using nitric oxide (NO), what role does $NO_2$ play according to the proposed mechanism?

It directly reacts with oxygen to form $SO_3$.

It acts as a final product that inhibits the reaction.

It serves as an intermediate, being both produced and consumed during the reaction. (correct)

It remains unchanged throughout the entire reaction.

Which characteristic is most crucial for a solid catalyst used in the hydrogenation of vegetable oil?

Inertness towards the reactants to avoid side reactions.

High density to ensure proper mixing.

Low porosity to prevent reactant adsorption.

Large surface area to facilitate effective interaction with reactants. (correct)

What is the primary function of the mixture of Pd, Pt, and Rh in an automobile catalytic converter?

To increase the fuel efficiency of the engine.

To absorb uncombusted hydrocarbons.

To convert toxic gases like NO and CO into less harmful substances. (correct)

To filter particulate matter from the exhaust gases.

Given the reactions:

$CO(g) + 3H_2(g) \xrightarrow{Ni-catalyst} CH_4(g) + H_2O(g)$

$CO(g) + 2H_2(g) \xrightarrow{ZnO-Cr_2O_3 Catalyst} CH_3OH(g)$

What can be concluded about catalysts?

Different catalysts can lead to different products from the same reactants. (C) Signup and view all the answers

In enzyme-catalyzed reactions, how do enzymes affect the activation energy?

Enzymes lower the activation energy, speeding up the reaction. (A) Signup and view all the answers

Which type of rate is most useful for determining the rate law of a reaction because it minimizes the impact of product concentrations?

Initial rate (B) Signup and view all the answers

A reaction's rate is measured at different times, and the data is plotted. How would you determine the instantaneous rate at a specific time point on the graph?

Determine the slope of the tangent line to the curve at that specific time point. (C) Signup and view all the answers

Consider a reaction where the concentration of a reactant decreases from 0.1 M to 0.05 M in 20 seconds. Which statement accurately describes how the average rate of this reaction should be expressed?

Average Rate = $(0.1 M - 0.05 M) / 20 s = 0.0025 M/s$ (C) Signup and view all the answers

In a study of chemical kinetics, why is it important to understand the stoichiometric relationships between reactants and products?

To accurately express the rates of consumption and formation of different substances in the reaction. (C) Signup and view all the answers

What is the primary purpose of determining the rate law for a chemical reaction?

To understand how the rate changes with varying reactant concentrations. (D) Signup and view all the answers

How does understanding the reaction mechanism aid in chemical kinetics?

It explains the sequence of elementary steps that dictates the reaction rate. (C) Signup and view all the answers

A chemist performs a reaction with and without a catalyst and measures the reaction rate in both scenarios. What key difference would be observed when a catalyst is used?

The catalyzed reaction proceeds at a faster rate due to a lower activation energy. (B) Signup and view all the answers

Why is the determination of activation energy important in chemical kinetics?

It helps to understand the temperature sensitivity of the reaction rate. (B) Signup and view all the answers

Why is determining the rate law of a reaction significant?

It provides insights into the sequence of steps involved in the reaction mechanism. (B) Signup and view all the answers

In the rate law expression, Rate = k[A]^x[B]^y, what do 'x' and 'y' represent?

The rate orders with respect to reactants A and B, respectively. (B) Signup and view all the answers

For the reaction 2N2O5 -> 4NO2 + O2, if the rate of formation of NO2 is 0.08 M/s, what is the rate of disappearance of N2O5?

0.04 M/s (D) Signup and view all the answers

Consider the rate law: Rate = k[A]^2[B]. What is the overall order of the reaction?

3 (B) Signup and view all the answers

In a zero-order reaction, how does changing the concentration of the reactant affect the reaction rate?

The reaction rate remains constant regardless of the concentration of the reactant. (D) Signup and view all the answers

Given the reaction aA + bB -> cC + dD, which expression accurately represents the relationship between the rates of disappearance of reactants and appearance of products?

$-\frac{1}{a}\frac{\Delta[A]}{\Delta t} = -\frac{1}{b}\frac{\Delta[B]}{\Delta t} = \frac{1}{c}\frac{\Delta[C]}{\Delta t} = \frac{1}{d}\frac{\Delta[D]}{\Delta t}$ (C) Signup and view all the answers

For a first-order reaction, if the rate constant k is 0.05 s^-1, what does this indicate about the reaction?

The rate of the reaction is directly proportional to the concentration of one reactant, and it proceeds at a certain rate defined by the rate constant. (D) Signup and view all the answers

Consider a reaction with the rate law Rate = k[A][B]^0. If the concentration of A is doubled, what happens to the reaction rate?

The reaction rate doubles. (C) Signup and view all the answers

In an experiment, the initial rate of a reaction between $S_2O_8^{2-}$ and $I^-$ is measured at two different concentrations of $S_2O_8^{2-}$, while keeping the $I^-$ concentration constant. If doubling the concentration of $S_2O_8^{2-}$ doubles the initial rate, what is the order of the reaction with respect to $S_2O_8^{2-}$?

First order (C) Signup and view all the answers

Consider a reaction where the rate law is given by $Rate = k[S_2O_8^{2-}] [I^-]$. If the initial concentrations are $[S_2O_8^{2-}] = 0.1 M$ and $[I^-] = 0.2 M$, and the rate constant $k = 5 \times 10^{-3} L \cdot mol^{-1} \cdot s^{-1}$, what is the initial rate of the reaction?

$1.0 \times 10^{-3} mol \cdot L^{-1} \cdot s^{-1}$ (D) Signup and view all the answers

For a zero-order reaction, a plot of reactant concentration $[R]_t$ versus time $t$ yields a straight line. What does the slope of this line represent?

The negative of the rate constant -k (B) Signup and view all the answers

The reaction between $S_2O_8^{2-}$ and $I^-$ is found to be first order with respect to both reactants. If the concentration of $S_2O_8^{2-}$ is doubled and the concentration of $I^-$ is halved, how will the rate of the reaction change?

The rate will remain the same (B) Signup and view all the answers

In a reaction with rate law $Rate = k[S_2O_8^{2-}] [I^-]$, the rate constant $k$ is determined to be $4.6 \times 10^{-3} L \cdot mol^{-1} \cdot s^{-1}$ at a certain temperature. If the concentrations of both $S_2O_8^{2-}$ and $I^-$ are $0.30 M$, what is the rate of the reaction?

$4.14 \times 10^{-4} mol \cdot L^{-1} \cdot s^{-1}$ (C) Signup and view all the answers

For the reaction $2NO_2(g) \rightarrow 2NO(g) + O_2(g)$, what is the correct interpretation of the rate law expression, Rate = $k[NO_2]^n$?

The rate of reaction depends on the concentration of $NO_2$ raised to the power of <code>n</code>, where <code>n</code> must be determined experimentally. (B) Signup and view all the answers

Consider a reaction where the rate law is given by Rate = $k[A]^2[B]$. What will happen to the reaction rate if the concentration of A is doubled and the concentration of B is halved?

The reaction rate will double. (C) Signup and view all the answers

Which statement best describes the relationship between differential and integrated rate laws?

Differential rate laws relate the reaction rate to the concentrations of reactants; integrated rate laws show how the concentrations of species change over time. (D) Signup and view all the answers

In determining the rate law for a reaction, why are the concentrations of products usually excluded?

The reverse reaction is negligible under the studied conditions. (A) Signup and view all the answers

For a reaction $R1 + R2 \rightarrow Products$, the experimentally determined rate law is Rate = $k[R1]^x[R2]^y$. What do the exponents x and y signify?

The rate orders with respect to the individual reactants R1 and R2, respectively. (C) Signup and view all the answers

If the average rate of a reaction decreases as the reaction progresses, which of the following is the most likely reason?

The concentration of reactants decreases. (A) Signup and view all the answers

The initial concentration of a reactant is 0.200 mol/L. After 60 seconds, the concentration drops to 0.100 mol/L. Assuming first-order kinetics, what is the approximate half-life of this reaction?

60 seconds (B) Signup and view all the answers

For the reaction $2NO_2(g) \rightarrow 2NO(g) + O_2(g)$, if the rate of formation of $O_2$ is $2.0 \times 10^{-6}$ mol/(L⋅s), what is the rate of decomposition of $NO_2$?

$4.0 \times 10^{-6}$ mol/(L⋅s) (C) Signup and view all the answers

For a reaction A → products, if the initial concentration of A is 8.0 M and after 60 seconds the concentration is 6.0 M, and the reaction is zero order, what is the rate constant (k)?

$3.33 \times 10^{-2} M/s$ (A) Signup and view all the answers

A reaction mechanism consists of several elementary steps. Which statement regarding the relationship between the elementary steps and the overall balanced equation is correct?

The sum of the elementary steps must equal the overall balanced equation. (B) Signup and view all the answers

Consider a reaction with the experimental rate law: Rate = k[A]^2[B]. Which of the following elementary steps is consistent with this rate law?

2A + B → Products (D) Signup and view all the answers

For the reaction $2N_2O_5(g) \rightarrow 4NO_2(g) + O_2(g)$, the proposed mechanism is:

Step 1: $N_2O_5 \rightleftharpoons NO_2 + NO_3$ (fast) Step 2: $NO_2 + NO_3 \rightarrow NO + O_2 + NO_2$ (slow) Step 3: $NO_3 + NO \rightarrow 2NO_2$ (fast)

What is the molecularity of the rate-determining step?

Bimolecular (B) Signup and view all the answers

What is the half-life of a first-order reaction if the rate constant is $7.0 \times 10^{-4} s^{-1}$?

990 s (C) Signup and view all the answers

Consider the following reaction mechanism:

Step 1: $A + B \rightarrow C$ (slow) Step 2: $C + A \rightarrow D$ (fast)

Which of the following rate laws is consistent with this mechanism?

Rate = k[A][B] (D) Signup and view all the answers

For a reaction to occur effectively, reactant molecules must collide with the proper orientation and sufficient energy. What is the term for the minimum energy required for a collision to result in a reaction?

Activation energy (D) Signup and view all the answers

A proposed mechanism for a reaction is:

Step 1: $Cl_2(g) \rightleftharpoons 2Cl(g)$ (fast equilibrium) Step 2: $Cl(g) + CHCl_3(g) \rightarrow HCl(g) + CCl_3(g)$ (slow) Step 3: $CCl_3(g) + Cl(g) \rightarrow CCl_4(g)$ (fast)

What is the overall order of the reaction predicted by this mechanism?

1.5 (B) Signup and view all the answers

Flashcards

Chemical Kinetics

The study of reaction rates and factors affecting them.

Reaction Rates

The change in concentration of reactants or products over time.