firstlaw

# firstlaw - Let us return once again to the standard model...

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Phase Transitions; First Law of Thermodynamics Phase Transitions All of us are aware of the three states (or phases) of matter: solid (S), liquid (L) and gas (G). There are other, less common, states of matter: superconductor, superfluid, and ferromagnet but we will concentrate on S,L, and G. The melting of a solid, boiling of a liquid, and sublimation of a solid are examples of first order phase transitions. For these, even if the material is already at the transition temperature (e.g. melting point, boiling point), additional heat must be provided or extracted in order for the phase transition to occur. This additional heat per kilogram is called a heat of transition or latent heat (L), where Q = m L. Comment: L has units of J/kg. Calorimetry experiments are somewhat more complicated when phase transitions occur.

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First Law of Thermodynamics
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Unformatted text preview: Let us return once again to the standard model in thermodynamics: a gas in a cylinder with a piston . As will be derived in class, the work done by the gas in pushing the piston to a new location is given by, V f W out = ∫ P(V) dV , V i That is the area under the P-V curve between V i and V f . The work is positive when the gas does work on the environment. If you heat the system then we take Q in >0. With this sign convention we write the first law of thermodynamics (conservation of energy) dE internal =dQ in – dW out , where again, Q in >0 heat the gas and W out >0 gas does work. This basic physics equation is one of the foundations of mechanical engineering. Thermodynamic Processes In class we define: Adiabatic Isothermal Cyclic Free Expansion Isobaric Isovolumetric EXAMPLES[in class]...
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