Q&A Hero

Q: The decay curve shown below approximates the decay of phosphorus-32. What is the approximate half-life of phosphorus-32? A) 14 days B) 27 days C) 35 days D) 37.5 days

Q: The decay curve shown below approximates the decay of iodine-123. What is the approximate half-life of iodine-123? A) 13 hours B) 26 hours C) 32.5 hours D) 35 hours

Q: The decay curve shown below approximates the decay of cobalt-60. What is the approximate half-life of cobalt-60? A) 5 years B) 12.5 years C) 15 years D) 17.5 years

Q: Which of the following figures represents the decay of by positron emission to give after three half-lives has passed? Unshaded spheres represent atoms and shaded spheres represent atoms. A) figure (1) B) figure (2) C) figure (3) D) figure (4)

Q: Which of the following figures represents the beta decay of to give after one half-life has passed? Unshaded spheres represent atoms and shaded spheres represent atoms. A) figure (1) B) figure (2) C) figure (3) D) figure (4)

Q: decays by electron capture to give . If unshaded spheres represent atoms and shaded spheres represent atoms, how many half-lives have passed in the following example? A) 1 half-life B) 2 half-lives C) 3 half-lives D) 4 half-lives

Q: decays by beta emission to give . If unshaded spheres represent atoms and shaded spheres represent atoms, how many half-lives have passed in the following example? A) 1 half-life B) 2 half-lives C) 3 half-lives D) 4 half-lives

Q: decays by alpha emission to give . If unshaded spheres represent atoms and shaded spheres represent atoms, how many half-lives have passed in the following example? A) 1 half-life B) 2 half-lives C) 3 half-lives D) 4 half-lives

Q: What is the time required to achieve the molecular mixture in drawing (d)? A) 4 min B) 5 min C) 7 min D) 8 min

Q: What is the order of reaction with respect to A? A) 0 B) 1/2 C) 1 D) 2

Q: Which drawing (a)-(d) represents the reaction mixture at t = 3 minutes? A) drawing (a) B) drawing (b) C) drawing (c) D) drawing (d)

Q: Which drawing (a)-(d) represents the reaction mixture at t = 2 minutes? A) drawing (a) B) drawing (b) C) drawing (c) D) drawing (d)

Q: Consider the first-order decomposition of A molecules (shaded spheres) in two vessels of equal volume. How will the half-life of decomposition in vessel (a) be affected if the volume of the vessel is decreased by a factor of 2? A) decrease by 1/2 B) increase by 2 C) increase by 4 D) stay the same

Q: Consider the first-order decomposition of A molecules (shaded spheres) in two vessels of equal volume. How will the rate of decomposition in vessel (a) be affected if the volume of the vessel is decreased by a factor of 2? A) decrease by 1/2 B) increase by 2 C) increase by 4 D) stay the same

Q: Consider the first-order decomposition of A molecules (shaded spheres) in two vessels of equal volume. What is the half-life of decomposition in vessel (b) relative to the half-life of decomposition in vessel (a)? A) half-life in vessel (b)/half-life in vessel (a) = 4:1 B) half-life in vessel (b)/half-life in vessel (a) = 2:1 C) half-life in vessel (b)/half-life in vessel (a) = 3:2 D) half-life in vessel (b)/half-life in vessel (a) = 1:1

Q: Consider the first-order decomposition of A molecules (shaded spheres) in two vessels of equal volume. What is the half-life of decomposition in vessel (b) relative to the half-life of decomposition in vessel (a)? A) half-life in vessel (b)/half-life in vessel (a) = 4:1 B) half-life in vessel (b)/half-life in vessel (a) = 2:1 C) half-life in vessel (b)/half-life in vessel (a) = 3:2 D) half-life in vessel (b)/half-life in vessel (a) = 1:1

Q: Consider the first-order reaction A → B in which A molecules (unshaded spheres) are converted to B molecules (shaded spheres). Given the following pictures at t = 0 seconds and t = 100 seconds, which picture represents the number of A and B molecules remaining at 200 seconds? A) picture a) B) picture b) C) picture c) D) picture d)

Q: Consider the first-order reaction A → B in which A molecules (unshaded spheres) are converted to B molecules (shaded spheres). Given the following pictures at t = 0 seconds and t = 100 seconds, which picture represents the number of A and B molecules remaining at 300 seconds? A) picture a) B) picture b) C) picture c) D) picture d)

Q: The following reaction is second order in A and first order in B:A + B -> Products Rate = k[A]2[B]What is the rate constant k of this reaction in vessel (b) relative to the rate constant k of this reaction in vessel (a)? Each vessel has the same volume. Shaded spheres represent A molecules, and unshaded spheres represent B molecules.A) rate constant k in vessel (b)/rate constant k in vessel (a) = 1:2B) rate constant k in vessel (b)/rate constant k in vessel (a) = 1:1C) rate constant k in vessel (b)/rate constant k in vessel (a) = 2:1D) rate constant k in vessel (b)/rate constant k in vessel (a) = 4:1

Q: The following reaction is second order in A and first order in B:A + B ->Products Rate = k[A]2[B]What is the rate constant k of this reaction in vessel (b) relative to the rate constant k of this reaction in vessel (a)? Each vessel has the same volume. Shaded spheres represent A molecules, and unshaded spheres represent B molecules.A) rate constant k in vessel (b)/rate constant k in vessel (a) = 1:2B) rate constant k in vessel (b)/rate constant k in vessel (a) = 1:1C) rate constant k in vessel b)/rate constant k in vessel (a) = 2:1D) rate constant k in vessel (b)/rate constant k in vessel (a) = 4:1

Q: The following reaction is second order in A and first order in B:A + B ->Products Rate = k[A]2[B]What is the rate constant k of this reaction in vessel (b) relative to the rate constant k of this reaction in vessel (a)? Each vessel has the same volume. Shaded spheres represent A molecules, and unshaded spheres represent B molecules.A) rate constant k in vessel (b)/rate constant k in vessel (a) = 1:2B) rate constant k in vessel (b)/rate constant k in vessel (a) = 1:1C) rate constant k in vessel (b)/rate constant k in vessel (a) = 2:1D) rate constant k in vessel (b)/rate constant k in vessel (a) = 4:1

Q: The following reaction is first order in A and first order in B:A + B ->Products Rate = k[A][B]What is the rate constant k of this reaction in vessel (b) relative to the rate constant k of this reaction in vessel (a)? Each vessel has the same volume. Shaded spheres represent A molecules, and unshaded spheres represent B molecules.A) rate constant k in vessel (b)/rate constant k in vessel (a) = 1:2B) rate constant k in vessel (b)/rate constant k in vessel (a) = 1:1C) rate constant k in vessel (b)/rate constant k in vessel (a) = 2:1D) rate constant k in vessel (b)/rate constant k in vessel (a) = 4:1

Q: The following reaction is first order in A and first order in B:A + B -> Products Rate = k[A][B]What is the rate constant k of this reaction in vessel (b) relative to the rate constant k of this reaction in vessel (a)? Each vessel has the same volume. Shaded spheres represent A molecules, and unshaded spheres represent B molecules.A) rate constant k in vessel (b)/rate constant k in vessel (a) = 1:2B) rate constant k in vessel (b)/rate constant k in vessel (a) = 1:1C) rate constant k in vessel (b)/rate constant k in vessel (a) = 2:1D) rate constant k in vessel (b)/rate constant k in vessel (a) = 4:1

Q: The following reaction is first order in A and first order in B:A + B -> Products Rate = k[A][B]What is the rate constant k of this reaction in vessel (b) relative to the rate constant k of this reaction in vessel (a)? Each vessel has the same volume. Shaded spheres represent A molecules, and unshaded spheres represent B molecules.A) rate constant k in vessel (b)/rate constant k in vessel (a) = 1:2B) rate constant k in vessel (b)/rate constant k in vessel (a) = 1:1C) rate constant k in vessel (b)/rate constant k in vessel (a) = 2:1D) rate constant k in vessel (b)/rate constant k in vessel (a) = 4:1

Q: The following reaction is second order in A and first order in B:A + B -> Products Rate = k[A]2[B]What is the initial rate of this reaction in vessel (b) relative to the initial rate of this reaction in vessel (a)? Each vessel has the same volume. Shaded spheres represent A molecules, and unshaded spheres represent B molecules present at the beginning of the reaction.A) rate in vessel (b)/rate in vessel (a) = 1:2B) rate in vessel (b)/rate in vessel (a) = 1:1C) rate in vessel (b)/rate in vessel (a) = 2:1D) rate in vessel (b)/rate in vessel (a) = 4:1

Q: The following reaction is first order in A and first order in B:A + B -> Products Rate = k[A][B]What is the initial rate of this reaction in vessel (b) relative to the initial rate of this reaction in vessel (a)? Each vessel has the same volume. Shaded spheres represent A molecules, and unshaded spheres represent B molecules present at the beginning of the reaction.A) rate in vessel (b)/rate in vessel (a) = 1:2B) rate in vessel (b)/rate in vessel (a) = 1:1C) rate in vessel (b)/rate in vessel (a) = 2:1D) rate in vessel (b)/rate in vessel (a) = 4:1

Q: The following reaction is first order in A and first order in B:A + B -> Products Rate = k[A][B]What is the initial rate of this reaction in vessel (b) relative to the initial rate of this reaction in vessel (a)? Each vessel has the same volume. Shaded spheres represent A molecules, and unshaded spheres represent B molecules present at the beginning of the reaction.A) rate in vessel (b)/rate in vessel (a) = 1:2B) rate in vessel (b)/rate in vessel (a) = 1:1C) rate in vessel (b)/rate in vessel (a) = 2:1D) rate in vessel (b)/rate in vessel (a) = 4:1

Q: What is the rate law for this reaction? A) Rate = k[A2]2 B) Rate = k[B2]2 C) Rate = k[A2][B2] D) Rate = k[A2]2[B2]2

Q: What is the overall order of reaction? A) 0 B) 1 C) 2 D) 3

Q: What is the order of reaction with respect to B2? A) 0 B) 1 C) 2 D) 3

Q: What is the order of reaction with respect to A2? A) 0 B) 1 C) 2 D) 3

Q: Over the time interval 300 to 400 seconds, the rate of reaction with respect to A is [A]/t =3.7 10-5 M/s. What is the rate of reaction with respect to A over the time interval 0 to 100 seconds?A) 0 M/sB) less than 3.7 10-5 M/sC) 3.7 10-5 M/sD) greater than 3.7 10-5 M/s

Q: Over the time interval 300 to 400 seconds, the rate of reaction with respect to A is [A]/t =3.7 10-5 M/s. What is the rate of reaction with respect to A over the time interval 700 to 800 seconds?A) 0 M/sB) less than 3.7 10-5 M/sC) 3.7 10-5 M/sD) greater than 3.7 10-5 M/s

Q: Over the time interval 300 to 400 seconds, the rate of reaction with respect to A is [A]/t =3.7 10-5 M/s. Over the same time interval what is the rate of reaction with respect to C, [C]/t?A) [C]/t = [A]/t = 3.7 10-5 M/sB) [C]/t = (1/4)([A]/t) = (1/4)(3.7 10-5 M/s) = 9.2 10-6 M/sC) [C]/t = (1/2)([A]/t) = (1/2)(3.7 10-5 M/s) = 1.8 10-5 M/sD) [C]/t = -(1/2)([A]/t) = -(1/2)(3.7 10-5 M/s) = -1.8 10-5 M/s

Q: Over the time interval 300 to 400 seconds, the rate of reaction with respect to A is [A]/t = 3.7 10-5 M/s. Over the same time interval what is the rate of reaction with respect to B, [B]/t?A) [B]/t = [A]/t = 3.7 10-5 M/sB) [B]/t = (1/4)([A]/t) = (1/4)(3.7 10-5 M/s) = 9.2 10-6 M/sC) [B]/t = (1/2)([A]/t) = (1/2)(3.7 10-5 M/s) = 1.8 10-5 M/sD) [B]/t = -(1/2)([A]/t) = -(1/2)(3.7 10-5 M/s) = -1.8 10-5 M/s

Q: Which equation best represents the reaction?A) 4A(g) -> B(g) + 2C(g)B) 4A(g) + B(g) -> 2C(g)C) 2C(g) -> 4A(g) + B(g)D) 2C(g) + B(g) -> 4A(g)

Q: Biological reactions are catalyzed by A) carbohydrates. B) enzymes. C) lipids. D) steroids.

Q: The Haber process is the synthesis of ammonia gas from hydrogen and nitrogen on a hot metal surface. What is the catalyst and what type of catalysis is occurring? A) H2, homogeneous B) N2, homogeneous C) NH3, homogeneous D) metal surface, heterogeneous

Q: A mechanism for a naturally occurring reaction that destroys ozone is:Step 1: O3(g) + HO(g) -> HO2(g) + O2(g)Step 2: HO2(g) + O(g) -> HO(g) + O2(g)Which species is a catalyst and what type of catalysis is occurring?A) HO, homogeneousB) HO, heterogeneousC) HO2, homogeneousD) HO2, heterogeneous

Q: An aqueous reaction occurs by a two-step mechanism, shown below.Step 1: A2X2 + Y -> A2X + XYStep 2: A2X2 + XY -> A2X + X2 + YWhat is the catalyst in this reaction?A) A2XB) X2C) XYD) Y

Q: Which of the following does not affect the rate of a bimolecular reaction? A) concentrations of reactants B) presence of a catalyst C) temperature D) All of these affect the rate.

Q: The decomposition of ozone in the stratosphere can occur by the following two-step mechanism:Br + O3 -> BrO + O2BrO + O -> Br + O2Which species is a catalyst in this mechanism?A) BrB) BrOC) OD) O3

Q: A mechanism for a naturally occurring reaction that destroys ozone is:Step 1: O3(g) + HO(g) ->HO2(g) + O2(g)Step 2: HO2(g) + O(g) -> HO(g) + O2(g)Which species is a catalyst?A) HOB) HO2C) OD) O3

Q: The decomposition of hydrogen peroxide is given by the following reaction:2 H2O2(aq) -> 2 H2O(l) + O2(g)In the presence of KI the reaction is thought to occur by the following mechanism:Step 1: H2O2 + I- -> H2O + IO-Step 2: IO- + H2O2 -> H2O + O2 + I-What is the role of I- in this mechanism?A) catalystB) frequency factorC) intermediateD) transition state

Q: A catalyst increases the rate of a reaction by providing a different reaction pathway that A) lowers only the activation energy. B) lowers only the energy of the products. C) lowers only the energy of the reactants. D) All of these are affected by the presence of a catalyst.

Q: The first-order isomerization reaction: cyclopropane -> propene, has a rate constant of1.10 10-4s-1 at 470C and an activation energy of 264 kJ/mol. What is the temperature of the reaction when the rate constant is equal to 4.36 10-3s-1?A) 126CB) 411CC) 510CD) 540C

Q: The first-order isomerization reaction: cyclopropane → propene, has a rate constant of 1.10 10-4s-1 at 470C and 5.70 10-4s-1 at 500C. What is the activation energy, Ea, for the reaction? A) 46 kJ/mol B) 110 kJ/mol C) 260 kJ/mol D) 380 kJ/mol

Q: The aquation of tris(1, 10-phenanthroline)iron(II) in acid solution takes place according to the equation:Fe(phen)32+ + 3 H3O+ + 3 H2O -> Fe(H2O)62+ + 3 phenH+.If the activation energy, Ea, is 126 kJ/mol and the rate constant at 30C is 9.8 10-3 min-1, what is the rate constant at 50C?A) 4.4 10-4 min-1B) 2.2 10-1 min-1C) 4.6 100 min-1D) 2.3 103 min-1

Q: The aquation of tris(1, 10-phenanthroline)iron(II) in acid solution takes place according to the equation:Fe(phen)32+ + 3 H3O+ + 3 H2O -> Fe(H2O)62+ + 3 phenH+If the activation energy, Ea, is 126 kJ/mol and the rate constant at 30C is 9.8 10-3 min-1, what is the frequency factor, A?A) 2 10-24 min-1B) 2 10-20 min-1C) 5 1019 min-1D) 5 1023 min-1

Q: The aquation of tris(1, 10-phenanthroline)iron(II) in acid solution takes place according to the equation:Fe(phen)32+ + 3 H3O+ + 3 H2O -> Fe(H2O)62+ + 3 phenH+If the activation energy is 126 kJ/mol and frequency factor is 8.62 1017 s-1, at what temperature is the rate constant equal to 3.63 10-3 s-1 for the first-order reaction?A) 0CB) 36CC) 50CD) 94C

Q: The reaction for the decomposition of dinitrogen monoxide gas to form an oxygen radical is: N2O(g) -> N2(g) + O(g). If the activation energy is 250 kJ/mol and the frequency factor is 8.0 1011 s-1, what is the rate constant for the first-order reaction at 1000 K?A) 1.1 10-3 s-1B) 7.0 10-2 s-1C) 1.6 1013 s-1D) 9.1 1024 s-1

Q: The reaction for the decomposition of dinitrogen monoxide gas to form oxygen radicals is:N2O(g) -> N2(g) + O(g). If the rate constant is 3.04 10-2 s-1 and the frequency factor is8.00 1011 s-1, what is the activation energy for the first-order reaction at 700C?A) 0.262 kJ/molB) 38.2 kJ/molC) 180 kJ/molD) 250 kJ/mol

Q: Which part of the Arrhenius equation contains a term which measures the number of molecules that have the correct orientation for reaction? A) activation energy B) e-Ea/RT C) frequency factor D) none of these

Q: Consider a bimolecular reaction in the gas phase. Which one of the following changes in condition will not cause an increase in the rate of the reaction? A) add a catalyst B) increase the temperature at constant volume C) increase the volume at constant temperature D) All of these will increase the rate of reaction.

Q: A common rule of thumb in organic chemistry is that increasing the temperature of a reaction at room temperature by 10C doubles the rate. Calculate Ea for a reaction that follows this rule of thumb Assume room temperature is 25C. A) 0.576 kJ B) 12.2 kJ C) 38.4 kJ D) 52.9 kJ

Q: When the temperature of a gas whose activation energy is 55 kJ/mol is increased from 300 K to 320 K, the fraction of collisions with sufficient energy to react A) decreases by a factor of 2. B) decreases by a factor of 4. C) increases by a factor of 2. D) increases by a factor of 4.

Q: What fraction of collisions will have sufficient energy to react for a gas whose activation energy is 68 kJ/mol at 25C? A) 1.2 10-12 B) 2.7 10-2 C) 0.96 D) 8.3 1011

Q: The fraction of collisions with sufficient energy to react is equal to A) A B) Ea C) e-Ea/RT D) p

Q: A gas molecule at 298 K and 1 atm pressure undergoes a collision with another gas molecule approximately every ________ seconds. A) 10-15 B) 10-9 C) 10-6 D) 10-3

Q: What factor affects the rate of a chemical reaction? A) collision frequency B) fraction of collisions with sufficient energy C) orientation of molecules D) All of these

Q: What is the minimum energy barrier that must be overcome for a chemical reaction to occur? A) activation energy B) net energy C) potential energy D) rate limiting energy

Q: A gaseous reaction occurs by a two-step mechanism, shown below.Step 1: AX +Y2 AXY2 fastStep 2: AXY2 + AX -> 2 AXY slowIncluding concentration of only reactants and products, what is the rate law for this reaction?A) Rate = k[AX][Y2]B) Rate = k[AXY2]/[AX][Y2]C) Rate = k[AX]2[Y2]D) Rate = k[AXY]2/[AXY2][AX]

Q: When the concentration of A is doubled, the rate for the reaction: 2 A + B -> 2 C quadruples.When the concentration of B is doubled the rate remains the same. Which mechanism below is consistent with the experimental observations?A) Step 1: A + B D (fast equilibrium)Step 2: A + D ->2 C (slow)B) Step 1: A + B -> D (slow)Step 2: A + D 2 C (fast equilibrium)C) Step 1: 2 A -> D (slow)Step 2: B + D -> E (fast)Step 3: E -> 2 C (fast)D) Step 1: 2 A D (fast equilibrium)Step 2: B + D -> E (slow)Step 3: E -> 2 C (fast)

Q: A three-step mechanism has been suggested for the formation of carbonyl chloride:Step 1: Cl2 ->2 Cl (fast, equilibrium)Step 2: Cl + CO -> COCl (fast, equilibrium)Step 3: COCl + Cl2 -> COCl2 + Cl (slow)What is the molecularity of the rate-determining step?A) unimolecularB) bimolecularC) termolecularD) none of these

Q: What is the rate law for the elementary reaction shown below?2 HI -> H2 + I2A) Rate = k[HI]B) Rate = k[HI]2C) Rate = k[H2][I2]D) Rate = k[H2][I2]/[HI]2

Q: Which general rate law below corresponds to an elementary bimolecular reaction? A) Rate = k[A] B) Rate = k[A][B][C] C) Rate = k[A]2[B] D) Rate = k[A][B]

Q: Which of the following statements are true about reaction mechanisms? I. A rate law can be written from the molecularity of the slowest elementary step. II. The final rate law can include intermediates. III. The rate of the reaction is dependent on the fastest step in the mechanism. IV. A mechanism can never be proven to be the correct pathway for a reaction. A) I, II, III B) II, IV C) I, III D) I, IV

Q: The slowest step in a reaction mechanism is called the ________ step. A) activation B) elementary C) rate law D) rate-determining

Q: A three-step mechanism has been suggested for the formation of carbonyl chloride:Step 1: Cl2 -> 2 ClStep 2: Cl + CO -> COClStep 3: COCl + Cl2 -> COCl2 + ClWhich species is an intermediate in the mechanism?A) ClB) COC) COClD) COCl2

Q: A mechanism for a naturally occurring reaction that destroys ozone is:Step 1: O3(g) + HO(g) -> HO2(g) + O2(g)Step 2: HO2(g) + O(g) -> HO(g) + O2(g)What is the molecularity of the overall reaction?A) unimolecularB) bimolecularC) none of these because molecularity is the difference of the exponents in the rate lawD) none of these because molecularity only refers to elementary steps

Q: The decomposition of ozone in the stratosphere can occur by the following two-step mechanism:Step 1: Br + O3 -> BrO + O2Step 2: BrO + O -> Br + O2Which species is an intermediate in this mechanism?A) BrB) BrOC) OD) O3

Q: A mechanism for a naturally occurring reaction that destroys ozone is:Step 1: O3(g) + HO(g) -> HO2(g) + O2(g)Step 2: HO2(g) + O(g) -> HO(g) + O2(g)Which species is an intermediate?A) HOB) HO2C) OD) O3

Q: The elementary reaction: 2 HI -> H2 + I2, is an example of a ________ reaction.A) unimolecularB) bimolecularC) termolecularD) tetramolecular

Q: The elementary reaction representing the formation of ozone: is an example of a ________ reaction. A) unimolecular B) bimolecular C) termolecular D) tetramolecular

Q: Which statement below regarding the half-life of a zeroth-order reaction is true? A) Each half-life is half as long as the preceding half-life. B) Each half-life is twice as long as the preceding half-life. C) Each half-life is four times as long as the preceding half-life. D) The half-life remains unchanged throughout the course of the reaction.

Q: For the zeroth-order reaction: A -> products, what will happen to the rate of reaction if the concentration of A is doubled?A) The rate will be halved.B) The rate will be doubled.C) The rate will be quadrupled.D) The rate will remain the same.

Q: For the zeroth-order reaction: C -> products, -[C]/t = k, which of the following graphs would be expected to give a straight line?A) [C] vs. tB) ln[C] vs. tC) 1/[C] vs. tD) [C]2 vs. t

Q: If the units for rate are M s-1, what are the units for the rate constant, k, for a zeroth-order reaction? A) s-1 B) M-1 C) M s-1 D) M-1 s-1

Q: For the hypothetical second order reaction: A -> products, the general rate law is: rate = k[A]2. How long is the third half-life of the reaction if [A]0 is 0.080 M and the first half-life is 22 minutes?A) 0.57 minB) 1.7 minC) 7.3 minD) 88 min

Q: Which statement below regarding the half-life of a second-order reaction is true? A) Each half-life is half as long as the preceding one. B) Each half-life is twice as long as the preceding one. C) Each half-life is four times as long as the preceding one. D) The length of the half-life remains unchanged throughout the course of the reaction.