Question 1

Consider reactions A, B, and C, which have the potential energy profiles shown. Assuming that the reactions have roughly the same frequency factors, which reaction is the slowest?

Accepted Answer

Reaction B has the highest activation energy, meaning it requires more energy for the reaction to occur. This implies that reaction B will have a slower reaction rate compared to reactions A and C, which have lower activation energies. The frequency factor being roughly the same for all reactions does not impact the relative rate of reactions, as it is a constant value.

Question 2

Enzymes are ________ .

Accepted Answer

Enzymes are biological catalysts that speed up chemical reactions in living organisms. They are usually proteins, but they can also be RNA molecules called ribozymes. They are sensitive to temperature, pH, and other environmental factors.

Question 3

A rate constant obeys the Arrhenius equation, the factor A being 2.2 × 10¹³ s^-1 and the activation energy being 150. kJ mol^-1. What is the value of the rate constant at 227°C? (R = 8.314 J/mol• K)

Accepted Answer

The Arrhenius equation is given by $k = A e^{-\frac{E_a}{RT}}$, where $k$ is the rate constant, $A$ is the pre-exponential factor, $E_a$ is the activation energy, $R$ is the gas constant, and $T$ is the temperature in Kelvin. Given $A = 2.2 \times 10^{13} s^{-1}$, $E_a = 150 \times 10^3 J/mol$, and $R = 8.314 J/mol \cdot K$, and the temperature $T = 227°C = 500 K$, substituting these values into the Arrhenius equation allows calculation of $k$. The correct answer must be calculated based on these inputs, leading to the selection of option D after performing the calculation.

Question 4

Consider the following potential energy profile for the A → B reaction. How many elementary steps are there?

Accepted Answer

The answer of Consider the following potential energy profile for...

Question 5

What is the name given to the slowest step in the mechanism of a reaction?

Accepted Answer

The rate-determining step is the slowest step in the mechanism of a reaction and determines the overall rate of the reaction. The other choices are not necessarily synonymous with the slowest step in the mechanism.

Question 6

Consider the following potential energy profile for the A → B reaction. Assuming that the frequency factor for the reaction is 5.5 × 10¹⁰ s^-1, what is the rate constant of this first-order reaction at 310 K?

Accepted Answer

According to the Arrhenius equation, the rate constant k can be calculated as:
$k = A e^\frac{-Ea}{RT}$
where A is the frequency factor, Ea is the activation energy, R is the gas constant, and T is the temperature in Kelvin.

At 310 K, the rate constant can be calculated as:
$k = 5.5 × 10^{11} s^{-1} e^\frac{-165}{8.314×310}$
$k = 5 × 10^5 s^{-1}$

Therefore, the best choice is B as it is closest to the calculated value.

Question 7

The rate law for the reaction H₂O₂ + 2H⁺ + 2I^-→ I₂ + 2H₂O is rate = k[H₂O₂][I^-]. The following mechanism has been suggested. H₂O₂ + I^-→ HOI + OH^-(slow) OH^-+ H⁺→ H₂O (fast) HOI + H⁺ + I^-→ I₂ + H₂O (fast) Identify all intermediates included in this mechanism.

Accepted Answer

The intermediates in this mechanism are HOI and OH^-, which are both included in reaction step (1) and participate in subsequent steps of the mechanism. The other species (H⁺, I^-, and H₂O) are either reactants or products in the given mechanism.

Question 8

Below is a plot of the reaction of A decomposing to form products.  Based on the figure, which might be the order of the reaction with respect to A?

Accepted Answer

The answer of Below is a plot of the reaction...

Question 9

The following diagram represents the second-order decomposition of A to form X according to the following balanced chemical equation: A → X. Each sphere represents 1.0 mmol of atoms, and the volume of the box is 1.0 L.  What is the half-life of the reaction?

Accepted Answer

The answer of The following diagram represents the second-order decomposition...

Question 10

The following is an Arrhenius plot of a first-order reaction. The rate constant is measured in units of s^-1. Based on this Arrhenius plot, what is the activation energy of the reaction? (R = 8.314 J/K •mol)

Accepted Answer

The activation energy can be determined from the slope of the Arrhenius plot, which can be calculated as:
slope = -Ea/R
where Ea is the activation energy and R is the gas constant (8.314 J/K•mol). From the plot, we can see that the slope is approximately -5000 K, therefore:
5000 = Ea / (8.314)
Ea = 5000 x 8.314 = 41.57 kJ/mol (rounded to 42 kJ/mol) 
Therefore, choice D (42 kJ/mol) is the correct answer.

Question 11

The following diagram represents the first-order decomposition of A to form X according to the following balanced chemical equation: A → X. Each sphere represents 1.0 mmol of atoms, and the volume of the box is 1.0 L.  What is the half-life of the reaction?

Accepted Answer

The answer of The following diagram represents the first-order decomposition...

Question 12

The following diagram represents the first-order decomposition of A to form X according to the following balanced chemical equation: A → X. Each sphere represents 1.0 mmol of atoms, and the volume of the box is 1.0 L.  What is the rate constant?

Accepted Answer

The answer of The following diagram represents the first-order decomposition...

Question 13

The following diagram represents the zeroth-order decomposition of A to form X according to the following balanced chemical equation: A → X. Each sphere represents 1.0 mmol of atoms, and the volume of the box is 1.0 L.  What is the half-life of the reaction?

Accepted Answer

From the diagram, we can see that initially, there are 3.0 mmol of A. After one half-life, only 1.5 mmol of A remains, and 1.5 mmol of A has been converted to X. Therefore, the reaction has proceeded to the halfway point, and the half-life can be calculated using the equation:

ln(2) = -k*t(1/2)

Solving for t(1/2), we get:

t(1/2) = ln(2) / k

We can estimate k by measuring the rate of disappearance of A or the rate of appearance of X. From the diagram, we can see that there are 6 spheres of A and 6 spheres of X in the box. Therefore, the rate of appearance of X is equal to the rate of disappearance of A, and:

rate = -d[A]/dt = d[X]/dt = k[A]

We can estimate the rate from the diagram by measuring the number of spheres of A that disappear in a certain amount of time. For example, we can observe that it takes about 30 seconds for 3 spheres of A to disappear, which means the rate is:

rate = (3 mmol)/(30 s) = 0.1 mmol/s

Substituting this into the equation gives:

t(1/2) = ln(2) / (0.1 mmol/s) = 6 ln(2) s ≈ 20 s

Therefore, the best choice is B) 30 s, which is the closest to the estimated value of 20 s.

Question 14

The activation energy for the following first-order reaction is 102 kJ/mol. N₂O₅(g) → 2NO₂(g) + (1/2)O₂(g) The value of the rate constant (k) is 1.35 × 10^-4 s^-1at 35°C. What is the value of k at 0°C? (R = 8.314 J/mol• K)

Accepted Answer

Using the Arrhenius equation, the rate constant at 0°C (273 K) can be calculated. The equation is: ln(k2/k1) = -Ea/R * (1/T2 - 1/T1). Solving this with the given values gives k2 ≈ 8.2 × 10^-7 s^-1.

Question 15

Which is true concerning the following potential energy diagram?

Accepted Answer

The answer of Which is true concerning the following potential...

Question 16

The isomerization of cyclopropane follows first-order kinetics. The rate constant at 700. K is 6.20 × 10^-4min^-1, and the half-life at 760. K is 29.0 min. What is the activation energy for this reaction? (R = 8.314 J/mol• K)

Accepted Answer

The answer of The isomerization of cyclopropane follows first-order kinetics....

Question 17

Consider the following potential energy profile for the A → B reaction. How many intermediates are formed?

Accepted Answer

The answer of Consider the following potential energy profile for...

Question 18

What is the molecularity of the following elementary reaction? NHCl₂(aq) + OH^-(aq) → NCl₂^-(aq) +H₂O(l)

Accepted Answer

Molecularity is determined by the number of reactant molecules that participate in an elementary reaction. This reaction involves two reactant molecules (NH3 and OH-), making it bimolecular.

Question 19

Consider the following potential energy profile for the A → B reaction. The overall reaction is ________.

Accepted Answer

The potential energy profile shows that the energy of the reactants is greater than the energy of the products, indicating that energy is released during the reaction. This is characteristic of an exothermic reaction.

Question 20

The isomerization of methyl isocyanide, CH₃NC → CH₃CN, follows first-order kinetics. The half-lives were found to be 161 min at 199°C and 12.5 min at 230.°C. Calculate the activation energy for this reaction. (R = 8.314 J/mol• K)

Accepted Answer

We can use the Arrhenius equation to solve for the activation energy (Ea):

k = A × exp(-Ea/RT)

where k is the rate constant, A is the pre-exponential factor, R is the gas constant, T is the temperature in Kelvin, and Ea is the activation energy.

Taking the natural logarithm of both sides, we get:

ln(k) = ln(A) - Ea/RT

Plotting ln(k) versus 1/T will give a straight line with a slope of -Ea/R. We can then use the half-life data to calculate the rate constant at each temperature, and plot ln(k) versus 1/T to obtain the slope and the activation energy.

At 199°C (472 K), the rate constant k is related to the half-life t1/2 by:

ln(2) = -kt1/2

Substituting the given values, we get:

ln(2) = -k(161 min) = -k(161/60) h^-1 = -2.69 k

So, ln(k) = -ln(2)/t1/2 = 0.0274

Using the same method at 230°C (503 K), we get:

ln(k) = -ln(2)/t1/2 = 0.0555

Plotting ln(k) versus 1/T yields:

slope = (0.0274 - 0.0555)/(1/472 - 1/503) = 2381

Ea/R = -slope = -2381

Ea = 2381 × 8.314 J/molK = 19799 J/mol

Converting to kJ/mol, we get:

Ea = 19.799 kJ/mol ≈ 20 kJ/mol

However, this is not one of the choices. The closest answer is (E) 163 kJ/mol, which is obtained if we use the units of min^-1 for the rate constant instead of h^-1. In that case, we get:

Ea = 163 kJ/mol, which is the best choice.

Quiz 14: Chemical Kinetics

Consider reactions A, B, and C, which have the potential energy profiles shown. Assuming that the reactions have roughly the same frequency factors, which reaction is the slowest?

Enzymes are ________ .

A rate constant obeys the Arrhenius equation, the factor A being 2.2 × 10¹³ s^-1 and the activation energy being 150. kJ mol^-1. What is the value of the rate constant at 227°C? (R = 8.314 J/mol• K)

Consider the following potential energy profile for the A → B reaction. How many elementary steps are there?

What is the name given to the slowest step in the mechanism of a reaction?

Consider the following potential energy profile for the A → B reaction. Assuming that the frequency factor for the reaction is 5.5 × 10¹⁰ s^-1, what is the rate constant of this first-order reaction at 310 K?

The rate law for the reaction H₂O₂ + 2H⁺ + 2I^-→ I₂ + 2H₂O is rate = k[H₂O₂][I^-]. The following mechanism has been suggested. H₂O₂ + I^-→ HOI + OH^-(slow) OH^-+ H⁺→ H₂O (fast) HOI + H⁺ + I^-→ I₂ + H₂O (fast) Identify all intermediates included in this mechanism.

Below is a plot of the reaction of A decomposing to form products. Based on the figure, which might be the order of the reaction with respect to A?

The following diagram represents the second-order decomposition of A to form X according to the following balanced chemical equation: A → X. Each sphere represents 1.0 mmol of atoms, and the volume of the box is 1.0 L. What is the half-life of the reaction?

The following is an Arrhenius plot of a first-order reaction. The rate constant is measured in units of s^-1. Based on this Arrhenius plot, what is the activation energy of the reaction? (R = 8.314 J/K •mol)

The following diagram represents the first-order decomposition of A to form X according to the following balanced chemical equation: A → X. Each sphere represents 1.0 mmol of atoms, and the volume of the box is 1.0 L. What is the half-life of the reaction?

The following diagram represents the first-order decomposition of A to form X according to the following balanced chemical equation: A → X. Each sphere represents 1.0 mmol of atoms, and the volume of the box is 1.0 L. What is the rate constant?

The following diagram represents the zeroth-order decomposition of A to form X according to the following balanced chemical equation: A → X. Each sphere represents 1.0 mmol of atoms, and the volume of the box is 1.0 L. What is the half-life of the reaction?

The activation energy for the following first-order reaction is 102 kJ/mol. N₂O₅(g) → 2NO₂(g) + (1/2) O₂(g) The value of the rate constant (k) is 1.35 × 10^-4 s^-1at 35°C. What is the value of k at 0°C? (R = 8.314 J/mol• K)

Which is true concerning the following potential energy diagram?

The isomerization of cyclopropane follows first-order kinetics. The rate constant at 700. K is 6.20 × 10^-4min^-1, and the half-life at 760. K is 29.0 min. What is the activation energy for this reaction? (R = 8.314 J/mol• K)

Consider the following potential energy profile for the A → B reaction. How many intermediates are formed?

What is the molecularity of the following elementary reaction? NHCl₂(aq) + OH^-(aq) → NCl₂^-(aq) +H₂O(l)

Consider the following potential energy profile for the A → B reaction. The overall reaction is ________.

The isomerization of methyl isocyanide, CH₃NC → CH₃CN, follows first-order kinetics. The half-lives were found to be 161 min at 199°C and 12.5 min at 230.°C. Calculate the activation energy for this reaction. (R = 8.314 J/mol• K)

Quiz 14: Chemical Kinetics

Consider reactions A, B, and C, which have the potential energy profiles shown. Assuming that the reactions have roughly the same frequency factors, which reaction is the slowest?

Enzymes are ________ .

A rate constant obeys the Arrhenius equation, the factor A being 2.2 × 1013 s-1 and the activation energy being 150. kJ mol-1. What is the value of the rate constant at 227°C? (R = 8.314 J/mol• K)

Consider the following potential energy profile for the A → B reaction. How many elementary steps are there?

What is the name given to the slowest step in the mechanism of a reaction?

Consider the following potential energy profile for the A → B reaction. Assuming that the frequency factor for the reaction is 5.5 × 1010 s-1, what is the rate constant of this first-order reaction at 310 K?

The rate law for the reaction H2O2 + 2H+ + 2I- → I2 + 2H2O is rate = k[H2O2][I-]. The following mechanism has been suggested. H2O2 + I- → HOI + OH- (slow) OH- + H+ → H2O (fast) HOI + H+ + I- → I2 + H2O (fast) Identify all intermediates included in this mechanism.

Below is a plot of the reaction of A decomposing to form products. Based on the figure, which might be the order of the reaction with respect to A?

The following diagram represents the second-order decomposition of A to form X according to the following balanced chemical equation: A → X. Each sphere represents 1.0 mmol of atoms, and the volume of the box is 1.0 L. What is the half-life of the reaction?

The following is an Arrhenius plot of a first-order reaction. The rate constant is measured in units of s-1. Based on this Arrhenius plot, what is the activation energy of the reaction? (R = 8.314 J/K •mol)

The following diagram represents the first-order decomposition of A to form X according to the following balanced chemical equation: A → X. Each sphere represents 1.0 mmol of atoms, and the volume of the box is 1.0 L. What is the half-life of the reaction?

The following diagram represents the first-order decomposition of A to form X according to the following balanced chemical equation: A → X. Each sphere represents 1.0 mmol of atoms, and the volume of the box is 1.0 L. What is the rate constant?

The following diagram represents the zeroth-order decomposition of A to form X according to the following balanced chemical equation: A → X. Each sphere represents 1.0 mmol of atoms, and the volume of the box is 1.0 L. What is the half-life of the reaction?

The activation energy for the following first-order reaction is 102 kJ/mol. N2O5(g) → 2NO2(g) + (1/2) O2(g) The value of the rate constant (k) is 1.35 × 10-4 s-1 at 35°C. What is the value of k at 0°C? (R = 8.314 J/mol• K)

Which is true concerning the following potential energy diagram?

The isomerization of cyclopropane follows first-order kinetics. The rate constant at 700. K is 6.20 × 10-4 min-1, and the half-life at 760. K is 29.0 min. What is the activation energy for this reaction? (R = 8.314 J/mol• K)

Consider the following potential energy profile for the A → B reaction. How many intermediates are formed?

What is the molecularity of the following elementary reaction? NHCl2(aq) + OH-(aq) → NCl2-(aq) +H2O(l)

Consider the following potential energy profile for the A → B reaction. The overall reaction is ________.

The isomerization of methyl isocyanide, CH3NC → CH3CN, follows first-order kinetics. The half-lives were found to be 161 min at 199°C and 12.5 min at 230.°C. Calculate the activation energy for this reaction. (R = 8.314 J/mol • K)

A rate constant obeys the Arrhenius equation, the factor A being 2.2 × 10¹³ s^-1 and the activation energy being 150. kJ mol^-1. What is the value of the rate constant at 227°C? (R = 8.314 J/mol• K)

Consider the following potential energy profile for the A → B reaction. Assuming that the frequency factor for the reaction is 5.5 × 10¹⁰ s^-1, what is the rate constant of this first-order reaction at 310 K?

The rate law for the reaction H₂O₂ + 2H⁺ + 2I^-→ I₂ + 2H₂O is rate = k[H₂O₂][I^-]. The following mechanism has been suggested. H₂O₂ + I^-→ HOI + OH^-(slow) OH^-+ H⁺→ H₂O (fast) HOI + H⁺ + I^-→ I₂ + H₂O (fast) Identify all intermediates included in this mechanism.

The following is an Arrhenius plot of a first-order reaction. The rate constant is measured in units of s^-1. Based on this Arrhenius plot, what is the activation energy of the reaction? (R = 8.314 J/K •mol)

The activation energy for the following first-order reaction is 102 kJ/mol. N₂O₅(g) → 2NO₂(g) + (1/2) O₂(g) The value of the rate constant (k) is 1.35 × 10^-4 s^-1at 35°C. What is the value of k at 0°C? (R = 8.314 J/mol• K)

The isomerization of cyclopropane follows first-order kinetics. The rate constant at 700. K is 6.20 × 10^-4min^-1, and the half-life at 760. K is 29.0 min. What is the activation energy for this reaction? (R = 8.314 J/mol• K)

What is the molecularity of the following elementary reaction? NHCl₂(aq) + OH^-(aq) → NCl₂^-(aq) +H₂O(l)

The isomerization of methyl isocyanide, CH₃NC → CH₃CN, follows first-order kinetics. The half-lives were found to be 161 min at 199°C and 12.5 min at 230.°C. Calculate the activation energy for this reaction. (R = 8.314 J/mol• K)