SLec5-6

# SLec5-6 - Lecture 5-6 The First Law of Thermodynamics Last...

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Lecture 5-6: The First Law of Thermodynamics Last time, we have discussed exact differentials and shown that they are the total differentials of some functions (that can be visualized like surfaces). In thermodynamics, such functions can be state variables , like U, P, V or T, that characterize equilibrium states of the systems . Their incremental changes are described by exact differentials - they can be formed by a sum of several inexact differentials Other variables, like work (w) or heat (q), are used in thermodynamics to describe processes , but not equilibrium states – therefore, their incremental changes ( δ w, δ q) can only be inexact differentials - they depend on the path that was taken = the realized process, and they can NOT be represented by functions = surfaces

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We denote work done by the surroundings on the system by (scalar product of the vector of external force, F ext , and the displacement, ds ). The pressure-volume work done by the external pressure on the gas is (if the gas increases / reduces its volume, then dV > 0 / dV < 0 and δ w < 0 / δ w > 0 ) Work When the external and internal pressures are almost the same, then the processes take part close to equilibrium and are reversible. Then, the
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## This note was uploaded on 09/23/2010 for the course CHEM 342 taught by Professor Prestonsnee during the Spring '08 term at Ill. Chicago.

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SLec5-6 - Lecture 5-6 The First Law of Thermodynamics Last...

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