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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.
-How is the activation energy for the decomposition of H₂O₂ affected by the addition of NaI to the coffee cup?

Question

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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. -How is the activation energy for the decomposition of H<sub>2</sub>O<sub>2</sub> affected by the addition of NaI to the coffee cup? A) Increased, because adding NaI changes the concentration of the reactants in the reaction vessel B) Increased, because NaI lowers the bond dissociation energy of H<sub>2</sub>O<sub>2</sub> C) Decreased, because NaI stabilizes the transition state of the reaction D) Decreased, because NaI increases the amount of heat produced from 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.
-How is the activation energy for the decomposition of H₂O₂ affected by the addition of NaI to the coffee cup?

Quizplus · Accepted Answer

11ecba2d_121a_bf6f_a3bf_c75314b9343d_MD0008_00 A catalyst is a compound that increases the rate of a reaction without being consumed by the reaction. It does this by lowering the reaction's activation energy (the difference between the energy of the transition state and the energy of the reactants). The transition state is an unstable, transient formation (activated complex) that is much higher in energy than the reactants. A catalyst stabilizes the transition state for a reaction (creating a less energetic transition state). After the products are formed, the catalyst is recovered. The iodide ion (I⁻) from NaI acts as a catalyst in the decomposition of H₂O₂ by stabilizing the transition state formed when the bonds in H₂O₂ break to form H₂O and O₂. This decreases the activation energy and increases the rate of the decomposition of H₂O₂. (Choice A) In the presence of NaI, the activation energy is decreased, not increased. Additionally, NaI does not change the amount of reactants or products, only the rate at which products form. (Choice B) Although the decomposition of H₂O₂ requires overcoming the bond dissociation energy of the H-O and O-O bonds, a catalyst such as NaI only serves to stabilize the transition state, causing the bonds to break more quickly. A catalyst does not change the inherent energy required to break the bonds. (Choice D) The activation decreases in the presence of NaI, but this decrease is not due to changes in the amount of heat that is produced in the reaction. The activation energy affects only the kinetics, not the enthalpy of the reaction. Educational objective: The activation energy of a reaction is the difference in energy between the reactants and the transition state of a reaction. Catalysts lower the activation energy by stabilizing the high-energy transition state.

Passage Living Organisms That Require Oxygen to Respire Can Build Up