Passage
Living organisms that require oxygen to respire can build up hydrogen peroxide (H₂O₂) as a byproduct of respiration. Because hydrogen peroxide can cause oxidative damage to cells, the amount of H₂O₂ in cells must be closely regulated. Although H₂O₂ decomposes spontaneously, a catalyst is needed for the reaction to occur at a sufficiently rapid rate suitable for biological purposes. In biological systems, an enzyme called a catalase accelerates the catalytic decomposition of H₂O₂ into water and oxygen (Reaction 1) .
Reaction 1In a laboratory setting, several different inorganic compounds can also serve as catalysts for H₂O₂ decomposition, allowing researchers to compare how different catalysts affect the efficiency of the reaction. To compare Fe(NO₃) ₃ (a metal homogeneous catalyst) and NaI (a halogen homogeneous catalyst) , researchers measured the amount of heat evolved after placing each catalyst in a fresh solution of 3% hydrogen peroxide.To perform the measurements, the researchers placed 50 mL of 3% H₂O₂ in an insulated coffee cup to be used as a calorimeter, as shown in Figure 1. Before adding any catalyst, the initial, baseline temperature of the H₂O₂ solution was determined by recording the temperature every 30 seconds for 5 minutes. Then 10 mL of 0.10 M Fe(NO₃) ₃(aq) catalyst was added to the H₂O₂ solution. The temperature was recorded every 30 seconds for another 15 minutes. The experiment was then repeated using 10 mL of 0.50 M sodium iodide in 0.01 M NaOH as the catalyst. The results for each reaction are shown in Figure 2.
Figure 1 Coffee cup calorimeter
Figure 2 Temperature vs. time measurements for reactions catalyzed by Fe(NO₃) ₃ and NaI
Adapted from: C. Marzzacco, "The effect of a change in catalyst on the enthalpy of decomposition of hydrogen peroxide." Chem13 News Magazine. ©2008 University of Waterloo.
-Which of the following statements explains why the change in temperature of the H₂O₂ decomposition reaction using Fe(NO₃) ₃ is approximately the same value as the change in temperature using NaI?

Question

Passage
Living organisms that require oxygen to respire can build up hydrogen peroxide (H₂O₂) as a byproduct of respiration. Because hydrogen peroxide can cause oxidative damage to cells, the amount of H₂O₂ in cells must be closely regulated. Although H₂O₂ decomposes spontaneously, a catalyst is needed for the reaction to occur at a sufficiently rapid rate suitable for biological purposes. In biological systems, an enzyme called a catalase accelerates the catalytic decomposition of H₂O₂ into water and oxygen (Reaction 1) .

Passage Living organisms that require oxygen to respire can build up hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) as a byproduct of respiration. Because hydrogen peroxide can cause oxidative damage to cells, the amount of H<sub>2</sub>O<sub>2</sub> in cells must be closely regulated. Although H<sub>2</sub>O<sub>2</sub> decomposes spontaneously, a catalyst is needed for the reaction to occur at a sufficiently rapid rate suitable for biological purposes. In biological systems, an enzyme called a catalase accelerates the catalytic decomposition of H<sub>2</sub>O<sub>2</sub> into water and oxygen (Reaction 1) . <strong>Reaction 1</strong>In a laboratory setting, several different inorganic compounds can also serve as catalysts for H<sub>2</sub>O<sub>2</sub> decomposition, allowing researchers to compare how different catalysts affect the efficiency of the reaction. To compare Fe(NO<sub>3</sub>) <sub>3</sub> (a metal homogeneous catalyst) and NaI (a halogen homogeneous catalyst) , researchers measured the amount of heat evolved after placing each catalyst in a fresh solution of 3% hydrogen peroxide.To perform the measurements, the researchers placed 50 mL of 3% H<sub>2</sub>O<sub>2</sub> in an insulated coffee cup to be used as a calorimeter, as shown in Figure 1. Before adding any catalyst, the initial, baseline temperature of the H<sub>2</sub>O<sub>2</sub> solution was determined by recording the temperature every 30 seconds for 5 minutes. Then 10 mL of 0.10 M Fe(NO<sub>3</sub>) <sub>3</sub>(aq) catalyst was added to the H<sub>2</sub>O<sub>2</sub> solution. The temperature was recorded every 30 seconds for another 15 minutes. The experiment was then repeated using 10 mL of 0.50 M sodium iodide in 0.01 M NaOH as the catalyst. The results for each reaction are shown in Figure 2. <strong>Figure 1</strong> Coffee cup calorimeter <strong>Figure 2</strong> Temperature vs. time measurements for reactions catalyzed by Fe(NO<sub>3</sub>) <sub>3</sub> and NaI Adapted from: C. Marzzacco, The effect of a change in catalyst on the enthalpy of decomposition of hydrogen peroxide. Chem13 News Magazine. ©2008 University of Waterloo. -Which of the following statements explains why the change in temperature of the H<sub>2</sub>O<sub>2</sub> decomposition reaction using Fe(NO<sub>3</sub>) <sub>3</sub> is approximately the same value as the change in temperature using NaI? A) Fe(NO<sub>3</sub>) <sub>3</sub> stabilizes the transition state more than NaI. B) Fe(NO<sub>3</sub>) <sub>3</sub> results in a faster reaction rate than NaI. C) Fe(NO<sub>3</sub>) <sub>3</sub> and NaI are both homogeneous catalysts. D) Fe(NO<sub>3</sub>) <sub>3</sub> and NaI do not affect the heat of the reaction.

Reaction 1In a laboratory setting, several different inorganic compounds can also serve as catalysts for H₂O₂ decomposition, allowing researchers to compare how different catalysts affect the efficiency of the reaction. To compare Fe(NO₃) ₃ (a metal homogeneous catalyst) and NaI (a halogen homogeneous catalyst) , researchers measured the amount of heat evolved after placing each catalyst in a fresh solution of 3% hydrogen peroxide.To perform the measurements, the researchers placed 50 mL of 3% H₂O₂ in an insulated coffee cup to be used as a calorimeter, as shown in Figure 1. Before adding any catalyst, the initial, baseline temperature of the H₂O₂ solution was determined by recording the temperature every 30 seconds for 5 minutes. Then 10 mL of 0.10 M Fe(NO₃) ₃(aq) catalyst was added to the H₂O₂ solution. The temperature was recorded every 30 seconds for another 15 minutes. The experiment was then repeated using 10 mL of 0.50 M sodium iodide in 0.01 M NaOH as the catalyst. The results for each reaction are shown in Figure 2.

Figure 1 Coffee cup calorimeter

Figure 2 Temperature vs. time measurements for reactions catalyzed by Fe(NO₃) ₃ and NaI
Adapted from: C. Marzzacco, "The effect of a change in catalyst on the enthalpy of decomposition of hydrogen peroxide." Chem13 News Magazine. ©2008 University of Waterloo.
-Which of the following statements explains why the change in temperature of the H₂O₂ decomposition reaction using Fe(NO₃) ₃ is approximately the same value as the change in temperature using NaI?

Quizplus · Accepted Answer

11ecba2d_121a_232e_a3bf_71e4db2b19c7_MD0008_00 In contrast to the thermodynamics of a reaction, which indicate whether a reaction will be spontaneous or not, the kinetics of a reaction describe how long a reaction will take to reach completion under given conditions. A reaction may be spontaneous, but it may also proceed so slowly that it does not reach completion in a reasonable amount of time. A catalyst increases the rate (kinetics) of the reaction by decreasing the activation energy required for the reaction to progress at a given temperature. However, a catalyst does not affect the amount of products produced or the enthalpy (thermodynamics) of the reaction. The decomposition of H₂O₂ is an exothermic reaction. No matter how long the decomposition takes, the reaction will produce a certain amount of heat per mole of reactants. This means that the identity of the catalyst does not affect the heat of the reaction. Therefore, the reaction using Fe(NO₃)₃ as the catalyst will result in the same change in temperature as the reaction using NaI as a catalyst, assuming the same amount of H₂O₂ is used. (Choice A) Although a catalyst stabilizes the high-energy transition state of a reaction, the extent to which a catalyst stabilizes the transition state does not affect the heat evolved from the reaction. (Choice B) The reaction rate achieved by a catalyst has no bearing on the heat evolved from the reaction. (Choice C) Although Fe(NO₃)₃ and NaI are both homogeneous catalysts (in the same phase as the reactants), the type of catalyst (homogeneous or heterogeneous) can affect only the rate of the reaction, not the heat of the reaction. Educational objective: A catalyst increases the rate of a reaction by lowering the activation energy needed for the reaction to occur. A catalyst does not change the amounts of the products produced or the enthalpy (heat) of the reaction.

Passage Living Organisms That Require Oxygen to Respire Can Build Up