Exam 12: Statistical Thermodynamics

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Calculate the translational partition function of a carbon dioxide, CO2, molecule in a sample of 0.250 mol of gas held in a vessel at a pressure of 1.00 bar and a temperature of 298 K.

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D

The monosaccharide ribose, C5H10O5 may exist in five distinct conformations. Two of these conformations are six-membered rings and two are five-membered rings, with the remaining conformation being a straight chain. In a solution at 25 C, a sample of ribose was found to exist as 60% α-D-ribopyranose and 21% β-D-ribopyranose. Calculate the difference in molar energy between these two conformations, which differ only in the orientation of the anomeric hydroxyl group

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C

Water, H2O, has a residual entropy of 3.4 J K-1 mol-1 at 0 K, which arises because each water molecule may be orientated in two distinct ways. Use the Boltzmann formula to predict the residual entropy of mono-deuterated water, HDO.

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The degeneracy of the lowest level of a Br atom is 4. The first excited electronic level lies the equivalent of 3685 cm-1 higher in energy and has a degeneracy of 2. Calculate the electronic partition function at a temperature of 2500 K.

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Calculate the contribution made by vibrational motion to the molar entropy of hydrogen iodide, HI, gas at a temperature of 500 K. The vibrational frequency of HI is 7.91 1012 s-1.

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Calculate the rotational partition function for acetylene, C2H2, at 298 K. The rotational constant of acetylene is 3.529 1010 Hz.

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Use statistical thermodynamics to derive an expression for the contribution to the molar heat capacity at constant volume of a diatomic molecule at a temperature of 298 K as a result of vibrational motion. Start by differentiating with respect to temperature the expression for the internal energy and substituting for the vibrational partition function.

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The vibrational modes of a methane molecule, CH4, are listed below. Calculate the vibrational partition function at 1000 K. Mode Degeneracy Vibrational Wavenumber / 1 3026 2 1583 3 3157 3 1367

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The harmonic vibrational wavenumber of an iodine, I2, molecule is 217 cm-1. Treating the molecule as a harmonic oscillator, calculate the vibrational partition function at 298 K.

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Calculate the standard molar Gibbs energy of argon gas, Ar, at a temperature of 298 K, relative to that at 0 K.

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