lecture notes-Chapter15_posted

# lecture notes-Chapter15_posted - Chapter 15 Thermodynamics...

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1 Chapter 15: Thermodynamics The First Law of Thermodynamics Thermodynamic Processes (isobaric, isochoric, isothermal, adiabatic) Reversible and Irreversible Processes Heat Engines Refrigerators and Heat Pumps The Carnot Cycle Entropy (The Second Law of Thermodynamics) The Third Law of Thermodynamics

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2 §15.1 The First Law of Thermodynamics The first law of thermodynamics says the change in internal energy of a system is equal to the heat flow into the system plus the work done on the system. W Q U + =
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4 Question 8 A gas expands, doing 100 J of work. How much heat must be simultaneously added to this system for its internal energy to increase by 200 J? A) 100J B) 200J C) 300J D) 400J
5 §15.2 Thermodynamic Processes A state variable describes the state of a system at time t, but it does not reveal how the system was put into that state. Examples of state variables: pressure, temperature, volume, number of moles, and internal energy.

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6 A PV diagram can be used to represent the state changes of a system, provided the system is always near equilibrium. The area under a PV curve gives the magnitude of the work done on a system. W>0 for compression and W<0 for expansion.
7 The work done on a system depends on the path taken in the PV diagram. The work done on a system during a closed cycle can be nonzero. To go from the state (V i , P i ) by the path (a) to the state (V f , P f ) requires a different amount of work then by path (b). To return to the initial point (1) requires the work to be nonzero.

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8 An isothermal process implies that both P and V of the gas change (PV T).
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10 §15.3 Thermodynamic Processes for an Ideal Gas No work is done on a system when its volume remains constant (isochoric process). For an ideal gas (provided the number of moles remains constant), the change in internal energy is . T nC U Q V = =
For a constant pressure (isobaric) process, the change in internal energy is W Q U + = . T nC Q P = C P is the molar specific heat at constant pressure . For an ideal gas C P = C V +R. T

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lecture notes-Chapter15_posted - Chapter 15 Thermodynamics...

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