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system
a quantity of matter or a region in space chosen for study
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surroundings
physical space outside the system boundary
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boundary
real or imaginary surface that separates the system from its surroundings. It may be fixed or movable.
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closed system
exchange of energy but NOT matter
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open system
(control volume), exchange of energy and matter
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control surface
boundary of an open system
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isolated system
can exchange NEITHER energy nor matter
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property
a characteristic of a system in equilibrium. It is independent of the path used to arrive at the system condition.
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Intensive property
independent of amount of material (i.e.temperature, pressure, age, color, etc.)
Ratio of two extensive = intensive
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extensive property
Dependent of amount of material (mass, volume, total energy, etc.)
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equilibrium
a system that maintains thermal (uniform temperature), mechanical (uniform pressure), phase (mass of two phases), and chemical equilibrium. Microscopic processes still occur and rate of process is balances by reverse process.
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Process
Any change from one state to another
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steady-flow process
operating for long periods of time under the same conditions
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state postulate
a thermodynamic state of a simple compressible sysem is completely specified by two independent, intensive properties
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cycle
a process with identical end states
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absolute pressure
- measured relative to absolute zero (absolute vacuum)
- P abs = P atm +/- P gage
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atmospheric pressure
aka gage or vacuum pressure
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Temperature
energy content of a mass
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heat
- (Q) transfer; the difference in temperature that causes energy to flow between bodies
- Also difference in enthalpy!
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zeroth law of thermo
if two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other
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Phase
physically homogeneous/mechanically separable part of system (i.e. vapor, liquid, mineral)
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component
Expresses compositional variations in system. H20 is one-component system, only if phases are interest
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Energy states
- Unstable: falling/rolling
- Stable: at rest in LOWEST energy state
- Metastable: in low-energy perch
- equilibrium is NOT steady state
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thermal equilibrium
No net transfer of energy as heat between two regions contacted by diathermic wall (same temp). Different temp, heat would flow from hot to cold region.
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Mechanical Equilibrium
Two regions separated by a wall have equal pressure. But if one region had high pressure, it would move the wall toward the region with low pressure.
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reversible
Idealized process, proceeds through sequence of equilibrium states. No finite deviation from equilibrium.
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spontaneous
real/natural process where internal state of system changes to approach equilibrium from initial non-equilibrium state
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Endothermic
absorbs heat (+Q, or delta H > 0 )
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Exothermic
releases heat (-Q, or delta H < 0)
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