1st%20Law%20Thermodynamics_1

1st%20Law%20Thermodynamics_1 - BME 100L: topic 1 First law...

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BME 100L: topic 1 First law of thermodynamics: the conservation of energy Lingchong You
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Central questions Consider a reaction: C (s, graphite) Æ C (s, diamond) • Thermodynamics : – Is this process possible? – If possible, what conditions should you use? – And, what is the extent of reaction you’d expect? • Kinetics (will discuss in detail later) – If a process is possible, how fast can it proceed? – Behavior of systems far from equilibrium
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Basic concepts in thermodynamics • System • Variables of state and their changes • Process •Wo rk • Heat • Equation of states • Energy
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1. System boundary system Surroundings (environment) System: a part of universe that we choose to study. For example: a cup of water, this computer, a cell, a chemical reaction, a desk, etc Surroundings: everything else Boundary : what separates a system from its surroundings.
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Classification of systems Open system exchanges mass and energy with surroundings (human, cells, computer, a tree, etc). All realistic systems are in fact open systems. <Idealized concepts> Closed system exchanges only energy with the surroundings (battery Æ assuming no wear-off) Isolated system doesn’t exchange mass or energy Note: you’ll notice that this course, and research in physical sciences in general, heavily relies on simplification and idealization . Properly set up, such idealization can drastically reduce the complexity of the problem of interest, without significantly affecting conclusions. Other examples include: equilibrium, steady state, ideal gas, reversible process, Carnot engine, etc
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Describing systems • For this course, we only consider systems with homogeneous distribution of properties. Variable of state : depends only on the state of the system, not on the path taken to reach that state (e.g. temperature, pressure, density, energy, or your age). – Extensive (depends on total amount of materials constituting the system): volume, mass, energy, etc – Intensive (independent of …): temperature, pressure, etc Energy (E) – the ability to do work (needs definition).
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Process (path) Initial state final state State variable 1 Isobaric constant P Isothermal constant T Isochoric constant V Adiabatic no heat exchange Cyclic final state = initial state State variable 2 Cyclic process No net change for any state variables State variable 2
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Equilibrium state is where system properties are independent of time and space, and there is no flow of energy or mass with the surroundings. Steady state is where system properties do not change over time. • An equilibrium state must be at steady state but the reverse is not necessarily true. For example, a steady-state system may have exchange of materials with the environment or has non- uniform distribution of some system properties.
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Reversible process … proceeds with an infinite number of steps, where the system is at equilibrium at each step.
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This note was uploaded on 08/03/2009 for the course BME 100 taught by Professor Yuan during the Spring '07 term at Duke.

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1st%20Law%20Thermodynamics_1 - BME 100L: topic 1 First law...

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