Chapter 3

# 2 casesofidealgasesvnrtp

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Unformatted text preview:  the case of a process at constant volume to dU ‐ TdS &lt; 0  If we now assume T to be constant, we get: d(U ‐ TS) &lt; 0  We then define a new thermodynamic function, A, the Helmholtz free  energy such that: A = U ‐ TS  The criteria for spontaneity for a process occurring at constant volume  and temperature is therefore dA &lt; 0. In contrast, a process occurring at  constant volume and temperature will be reversible or will have reached  some equilibrium state if dA = 0.    Marand’s Notes: Chapter 3 ‐ The Second Law of Thermodynamics  118    Gibbs Free Energy:  We now consider processes occurring at constant pressure and constant  temperature. For constant pressure processes, the heat exchanged with the  surroundings is equal to the change in enthalpy.  δqP = dH  Therefore, the Clausius Inequality for a spontaneous process, which occurs  at constant pressure, is written as:  dS &gt; dH / T        which is equivalent to:  dH ‐ T dS &lt; 0  If the process furthermore occurs at constant temperature then:  d(H‐TS) &lt; 0  We then define a new thermodynamic state function, G = H ‐ TS, which we  call the Gibbs Free Energy.  The criteria for spontaneity for a process occurring at constant pressure  and temperature is therefore dG &lt; 0. In contrast, a process occurring at  constant pressure and temperature will be reversible or will have reached  some equilibrium state if dG = 0.    Marand’s Notes: Chapter 3 ‐ The Second Law of Thermodynamics  119  Maximum Work Functions, Δ A and Δ G  Beside...
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## This note was uploaded on 01/26/2014 for the course CHEM 3615 taught by Professor Aresker during the Spring '07 term at Virginia Tech.

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