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.
-The experiment was repeated with 3.0 g of solid MnO₂ particles added as an alternative catalyst. When MnO₂ was ground to a fine powder, the temperature rose more quickly than when the particles were not ground. The most likely reason for this is that with heterogeneous catalysts:

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. -The experiment was repeated with 3.0 g of solid MnO<sub>2</sub> particles added as an alternative catalyst. When MnO<sub>2</sub> was ground to a fine powder, the temperature rose more quickly than when the particles were not ground. The most likely reason for this is that with heterogeneous catalysts: A) the rate increases when the catalyst is oxidized. B) the rate increases as the catalyst surface area is increased. C) the rate decreases due to competing side reactions. D) the rate decreases when the catalyst is insoluble.

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.
-The experiment was repeated with 3.0 g of solid MnO₂ particles added as an alternative catalyst. When MnO₂ was ground to a fine powder, the temperature rose more quickly than when the particles were not ground. The most likely reason for this is that with heterogeneous catalysts:

Quizplus · Accepted Answer

11ecba2d_121b_5bb0_a3bf_6bb31ddda3d6_MD0008_00 Catalysts can be either homogenous or heterogeneous. A homogenous catalyst is in the same phase as the reactants. A heterogeneous catalyst is a catalyst that is in a different phase than the reactants. Heterogeneous catalysts are usually solids interacting with reactants that are either liquids or gases. The reactants adsorb onto the solid catalyst surface, which will either promote the interaction of two reactants or will weaken the bonds in the reactants. Both aspects serve to increase the reaction rate by stabilizing the high-energy transition state. Because adsorption occurs when one chemical substance collects on the surface of another substance (such as a solid catalyst), having more surface area available will allow more molecules to collect on the surface. Accordingly, increasing the surface area of a catalyst increases the rate of the reaction. In this case, MnO₂ serves as a heterogeneous solid catalyst for the decomposition of H₂O₂. The question says that the temperature increased more quickly, indicating that the reaction rate was higher when the catalyst was ground to a fine powder. The smaller particles of MnO₂ provided more surface area to be exposed to H₂O₂ molecules, which allowed the reaction to proceed at a faster rate. (Choice A) Using a fine powder instead of larger particles is a physical change to the catalyst, not a chemical change. The chemical (redox) properties of the catalyst do not explain why the physical change in the catalyst influenced the reaction rate. (Choice C) In this case, there is only one reactant and no major competing side reactions that would affect the rate of the reaction. (Choice D) The solubility of a homogeneous catalyst can affect the rate of the reaction because higher solubility can increase the interactions between reactant and catalyst species in solution. However, this question involves a heterogeneous catalyst, so the surface area is more important than solubility. Educational objective: A heterogeneous catalyst is in a different phase than the reactants whereas a homogeneous catalyst is in the same phase as the reactants. Heterogeneous catalysts involve the adsorption of reactants onto the surface of the catalyst and provide higher reaction rates with increased surface area.

Passage Living Organisms That Require Oxygen to Respire Can Build Up