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Thermodynamics Primer (1/4)

Thermodynamics Primer (1/4). process : change of state: physical (e.g. melting, freezing, expansion) chemical (new substance formed) work : ability to change height of mass in surroundings i.e. transfer of energy that involves organized motion

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Thermodynamics Primer (1/4)

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  1. Thermodynamics Primer (1/4) process: change of state: physical (e.g. melting, freezing, expansion) chemical (new substance formed) work: ability to change height of mass in surroundings i.e. transfer of energy that involves organized motion system: volume that we are interested in surroundings: everything else, where we make observations energy: capacity to do work heat: thermal form of energy; transfer of energy that makes use of chaotic motion of molecules endothermic: describes a process that absorbs energy exothermic: describes a process that releases energy internal energy U ≡ total energy of a system 1st Law: DU = q + w => the change in U is equal to the energy that passes through a system’s boundary as heat or work => the total energy of an isolated system is constant

  2. Thermodynamics Primer (2/4) enthalpy H ≡ U + PV Heat supplied at constant pressure (so long as the system does no additional work) heat capacity @ const. pressure cp ≡ (∂H/∂T)P Release of heat => a decrease in enthalpy of a system at const. pressure DH < 0 : exothermic DH > 0 : endothermic 2nd Law of Thermo: You can’t convert heat into work without some loss. direction of spontaneous change: toward a more disordered form (work not required) DStot > 0 (total entropy of an isolated system) => irreversible changes generate entropy => reversible changes do not generate entropy # of ways a system can be arranged to achieve same energy lvl S = k ln W k = 1.38 · 10-23 [J/K]

  3. Thermodynamics Primer (3/4) Thermodynamic Definition of entropy dS ≡ dq / T => DS = ∫dq / T Heat supplied at constant pressure (so long as the system does no additional work) 3rd law of thermo: at T = 0 K, all thermal motions cease => since S = k ln W , S = 0 ! Gibbs Free Energy: G=H-TS dG=dH-TdS-SdT H=U+PV dH=dU+PdV+VdP dG=dU+PdV+VdP-TdS-SdT dU=TdS-PdV dG=VdP-SdT Gibbs-Helmholz Eqn.: (T-dependence of GFE)

  4. Thermodynamics Primer (4/4) chemical potential of a substance j: (n’ : all other components) fundamental eqn. of thermodynamics: Always try to think in terms of G.F.E. to explain phenomena!

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