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1A_exercise_key_6 - 1 Chapter 6 Exercise Key Chapter 6...

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Chapter 6 Exercise Key 1 Chapter 6 Exercise Key Exercise 6.1 – Kinetic and Potential Energy: For each of the following situations, you are asked which pair has the higher energy. Explain your answer with reference to the capacity of each to do work and say whether the energy that distinguishes them is kinetic energy or potential energy. a. Nitric acid molecules, HNO 3 , in the upper atmosphere decompose to form HO molecules and NO 2 molecules by breaking a bond between the nitrogen atom and one of the oxygen atoms. Which has higher energy, a nitric acid molecule or the HO molecule and NO 2 molecule the come from its decomposition? HNO 3 (g) HO (g) + NO 2 (g) HO and NO 2 have higher potential energy than HNO 3 . When a system shifts to decrease the strengths or number of attractions between the system’s components, the potential energy in the system increases. Energy is required to separate the nitrogen and oxygen atoms being held together by mutual attraction in a chemical bond. The energy supplied goes to an increased potential energy of the separate HO and NO 2 compared to HNO 3 . If the bond is reformed, the potential energy is converted into a form of energy that could be used to do work. b. Nitrogen oxides, NO (g) and NO 2 (g) , are released into the atmosphere in the exhaust of our cars. Which has higher energy, a NO 2 molecule moving at 439 m/s or the same NO 2 molecule moving at 399 m/s. (These are the average velocities of NO 2 molecules at 80 ° C and 20 ° C.) A nitrogen dioxide molecule with a velocity of 439 m/s has greater kinetic energy than the same molecule with a velocity of 399 m/s. Any object in motion can collide with another object and move it, so any object in motion has the capacity to do work. This capacity to do work resulting from the motion of an object is called kinetic energy, KE. The particle with the higher velocity will move another object (like another molecule) farther, so it can do more work. It must therefore have more energy. c. Which has higher energy, a nitrogen monoxide molecule, NO, moving out your car’s tailpipe at 450 m/s or a nitrogen dioxide molecule, NO 2 , moving at the same velocity? The more massive nitrogen dioxide molecule has greater kinetic energy than the less massive nitrogen monoxide molecule with the same velocity. The moving particle with the higher mass can move another object (like another molecule) farther, so it can do more work. It must therefore have more energy.
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