Chapters 6-7

# Chapters 6-7 - Chapter 6 Thermochemistry-Energycapacity to...

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Chapter 6: Thermochemistry -Energy—capacity to do work, the capacity to move something -Potential energy—possessed by objects that can do work either because of their composition or because of their location -Kinetic Energy—is possessed by moving objects Examples: Page 216 of Potential & Kinetic energies Kinetic Energy = E K = ½ (mv 2 ) Units are in kg * m 2 s 2 1kgm 2 /s 2 = 1 Joule (SI unit for energy) Work = (force)(distance) Force – 1kg*ms -2 (this is a newton N) and distance = meter m kgm 2 /s 2 = 1 Joule -Balancing balls is an example of potential energy converting to kinetic energy and vice versa *you never destroy energy or create it* -Some energy is given off as heat or friction Thermochemistry: -A study of energy changes that occur during physical processes and chemical reactions -Branch off thermodynamics -System—part of the universe we are studying (see page 217 for examples) -Surroundings—rest of the universe -Interactions—exchange of energy/matter or both between a system and its surroundings (see page 217) -Open System—can exchange either matter or energy or both with its surroundings. -Closed System—may exchange energy but NOT matter with the surroundings -Isolated System—exchanges neither matter nor energy with its surroundings (217-218 examples) -Internal Energy (u)—of a system is the total energy contained within the system partly as kinetic energy and partly as potential energy (figure 6.4 page 218) Kinetic Energy: -Translational motion, rotational motion, vibrational motion -Collection called thermal energy Potential Energy: -Intramolecular forces, and intermolecular forces -Collectively called chemical energy -Heat (q)—quantity of energy transferred between a system and its surroundings as a result of a temperature difference between them. -Heat passes spontaneously from regions of higher temperature to regions of lower temperature -Heat transfer stops when the system and its surroundings reach the same temperature at thermal equilibrium -Work (w)—energy transfer between a system and its surrounding -A system does not contain work (has energy (system) but does NOT contain work) -In this chapter we are ONLY considering pressure & volume work. -Work done when gases either expand or are compressed Pressure = Force/area Force = Pressure x Area 1

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Work = Force x distance (h) height = Pressure x area x height Figure 6.8 page 220 -Difference in height = distance (h) used to do calculation h = change in volume delta v. -H represents the change in volume of gas so work = -pressure * delta v OR w=(-p)deltav -So when delta v is positive expanding gas work is negative therefore the system loses energy, and energy goes from the system to its surroundings -When delta v is negative compressed gas work is positive and energy is gained by the system from its surroundings. Example Question: (Insert Equation)
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Chapters 6-7 - Chapter 6 Thermochemistry-Energycapacity to...

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