CHEM 108 1st Edition Lecture 27Chapter 18: ThermodynamicsStatistical Entropy:- Boltzmann Equation: S = kb(ln W)o S = entropy o W = # of microstates.o k = Boltzmann constant (1.38 × 10-23 J/K) kb= gas constant/ Avogadro’s number = R/NAo This equation indicates that entropy increases as the number of microstates increases.- Statistical entropy states that in terms of potential energy it matters how the particles are oriented in a system- Macrostate: number of particles in the systemo A system with higher Macrostate has a higher entropy - Microstate: arrangement of particles in the system. - Two systems with the same Macrostate could have one with higher entropy due to it being able to have many different microstates.Thermodynamic interpretation of Second Law:- A process will be spontaneous if |q/T| transferred to or from the surroundings is greater than the |q/T| transferred from or to the surroundings (irreversible process, constant T) - exothermic process: q is negative, system decreases its entropy, surroundings increase its entropy - endothermic process: q is positive, system increases its entropy, surroundings decrease its entropy- ΔS = q/T- q is given by enthalpy change of phase transition - T is given by the temperature of the phase transitionFactors Affecting Entropy: - Temperature: Entropy increases as T increases. o Increases in kinetic energy increase the number of accessible microstates. o Decreasing temperature decreases entropy.- Volume: Entropy increases as volume increases. - Number of particles: Entropy increases as the number of particles increases. - Higher degree of freedom, higher entropy - Greater number of moles, higher degree of freedomThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Thermodynamic Entropy: - Isothermal Process: A process that takes place at constant T. - Reversible Process: A process that can be run in the reverse direction with no net heat flow into or out of the system.- For an isothermal process: ΔSsys= qrev/T o qrev = flow of heat for reversible process.Third Law of Thermodynamics:- The entropy of a perfect crystal is zero at absolute zero. - 3rd Law: Entropy of the universe increases for a spontaneous process.o ΔSuniv = ΔSsys + ΔSsurr- Absolute Entropy: The entropy of a substance at some temperature above 0 Kelvin. o Calculated from measurement of molar heat capacities as a function of temperature. - Standard Molar Entropy (S°): The absolute entropy of 1 mole of a substance in its standard state at 298 K and 1 bar of pressure.- Consider an ice cube melting at 0.0°C (273 K) on a counter top at room temperature (293 K). o Heat flows into ice cube: ΔSsys = qrev/273 o Heat flows out of counter top: ΔSsurr = −qrev/293 o ΔSuniv= (qrev/273) + (−qrev/293) > 0
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