Passage
Combustion occurs when an oxidation-reduction reaction takes place between a reduced fuel source and an oxidizer, most frequently oxygen. The reaction between hydrogen and oxygen forms water (Reaction 1) and is highly exothermic and thermodynamically favorable. At the completion of hydrogen combustion, essentially all H₂ molecules have been converted to water. Nevertheless, at room temperature and atmospheric pressure, molecular hydrogen and oxygen can coexist quite stably.2 H₂ + O₂ → 2 H₂OReaction 1A group of researchers designed two prototype internal combustion engines, each of which could inject a hydrogen/oxygen mixture into a 5-mL combustion chamber at a total pressure of 1 atm and could repeat this process for several cycles. In one engine design, a spark was generated to initiate combustion as hydrogen and oxygen were injected. In another method, the combustion chamber was coated with a small amount of platinum powder. Platinum dramatically increases the reaction rate at room temperature without the need for a spark. The platinum itself is not altered by the reaction and can be reused. Researchers measured the maximum power output of both engine designs under identical injection and temperature conditions (Figure 1) .
Figure 1 Relative power outputs of hydrogen engines with different ignition sources at 298 KThe power output of an engine is directly related to the rate of combustion. In the presence of platinum, researchers measured the engine's rate of water production at various temperatures and H₂/O₂ mixture compositions. The results are shown in Figure 2.
Figure 2 Rate of combustion in platinum-coated engines under various conditions
Adapted from Schultze M, Mantzaras J. Hetero-/homogeneous combustion of hydrogen/air mixtures over platinum: Fuel-lean versus fuel-rich combustion modes doi: 10.1016/j.ijhydene.2013.06.069
-When the platinum-based engine is run continuously at 300 K for 1 hour with 0.5 atm of H₂ and 0.5 atm of O₂ injected for each reaction, approximately what mass of water will be produced?

Question

Passage
Combustion occurs when an oxidation-reduction reaction takes place between a reduced fuel source and an oxidizer, most frequently oxygen. The reaction between hydrogen and oxygen forms water (Reaction 1) and is highly exothermic and thermodynamically favorable. At the completion of hydrogen combustion, essentially all H₂ molecules have been converted to water. Nevertheless, at room temperature and atmospheric pressure, molecular hydrogen and oxygen can coexist quite stably.2 H₂ + O₂ → 2 H₂OReaction 1A group of researchers designed two prototype internal combustion engines, each of which could inject a hydrogen/oxygen mixture into a 5-mL combustion chamber at a total pressure of 1 atm and could repeat this process for several cycles. In one engine design, a spark was generated to initiate combustion as hydrogen and oxygen were injected. In another method, the combustion chamber was coated with a small amount of platinum powder. Platinum dramatically increases the reaction rate at room temperature without the need for a spark. The platinum itself is not altered by the reaction and can be reused. Researchers measured the maximum power output of both engine designs under identical injection and temperature conditions (Figure 1) .

Figure 1 Relative power outputs of hydrogen engines with different ignition sources at 298 KThe power output of an engine is directly related to the rate of combustion. In the presence of platinum, researchers measured the engine's rate of water production at various temperatures and H₂/O₂ mixture compositions. The results are shown in Figure 2.

Figure 2 Rate of combustion in platinum-coated engines under various conditions
Adapted from Schultze M, Mantzaras J. Hetero-/homogeneous combustion of hydrogen/air mixtures over platinum: Fuel-lean versus fuel-rich combustion modes doi: 10.1016/j.ijhydene.2013.06.069
-When the platinum-based engine is run continuously at 300 K for 1 hour with 0.5 atm of H₂ and 0.5 atm of O₂ injected for each reaction, approximately what mass of water will be produced?

Quizplus · Accepted Answer

11ecba2d_11b4_5bfa_a3bf_cf5b233e6ef9_MD0008_00 The amount of product formed over the course of a reaction can be calculated as the reaction rate multiplied by the time the reaction is allowed to occur. Figure 2 shows that at 300 K and 0.5 atm of each reactant injected per reaction, the platinum-based engine produces water at a rate of 6 mmol/min. If the reaction proceeds for 1 hour, it will produce: 6 mmol/min × 60 min = 360 mmol of water To determine the mass of water produced, the molar amount must be multiplied by the molecular weight. Water has a molecular weight of 18 g/mol, or 18 mg/mmol: 360 mmol × 18 mg/mmol = 6,480 mg For the final answer, convert to grams: 6,480 mg × 1 g/1,000 mg = 6.48 g ≈ 6.5 g (Choices A and C) The reaction produces 0.36 mol, or 360 mmol, of water in 1 hour. The question asks for mass in grams. (Choice D) This value is the approximate mass of water produced in milligrams, not grams. Educational objective: Given a constant reaction rate, the amount of product formed during a reaction can be calculated as the rate multiplied by the time in which the reaction proceeds. Units may need to be converted between mass and moles.

Passage Combustion Occurs When an Oxidation-Reduction Reaction Takes Place Between a a Reduced