/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} 6.26 For a CO molecule, the constant... [FREE SOLUTION] | 91Ó°ÊÓ

91Ó°ÊÓ

For a COmolecule, the constant €is approximately 0.00024eV.(This number is measured using microwave spectroscopy, that is, by measuring the microwave frequencies needed to excite the molecules into higher rotational states.) Calculate the rotational partition function for a COmolecule at room temperature (300K), first using the exact formula 6.30 and then using the approximate formula 6.31

Short Answer

Expert verified

The rotational partition function of a heterogeneous diatomic molecule

Step by step solution

01

Rotational partition function:

The equation is

Zrot=∑j=0∞(2j+1)exp-j(j+1)∈kT

Here, ∈is the rotational constant, kis the Boltzmann constant, and Tis the absolute temperature.

At higher temperatures, for kT>>∈, the rotational partition function becomes as follows:

Zrot=kT∈

Substitute 8.617×10-5eV/Kfork,300Kfor T, and 0.00024eVin the equationZrot=kT∈

Zrot=(8.617×10-5eV/K)(300K)0.00024eV=107.7

Therefore, the rotational partition function of a COmolecule is107.7

02

The rotational partition function of a heterogeneous diatomic molecule:

The equations are

Zrot=∑j=0∞(2j+1)exp-j(j+1)∈kT

Expand the above summation from j=0to j=50:

Zrot=1+3exp-2∈kT+5exp-6∈kT+7exp-12∈kT+...101exp-2550∈kT

Substitute 107.7for kT∈in the above equation.

Zrot=1+3exp-2107.7+5exp-6107.7+7exp-12107.7+...101exp-2550107.7

=108.03

Therefore, the exact value of rotational partition function of a COmolecule is108.03

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with 91Ó°ÊÓ!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

Use Boltzmann factors to derive the exponential formula for the density of an isothermal atmosphere, already derived in Problems 1.16 and 3.37. (Hint: Let the system be a single air molecule, let s1 be a state with the molecule at sea level, and let s2 be a state with the molecule at height z.)

Prove that, for any system in equilibrium with a reservoir at temperature T, the average value of the energy is

E¯=-1Z∂Z∂β=-∂∂βlnZ

where β=1/kT. These formulas can be extremely useful when you have an explicit formula for the partition function.

Estimate the partition function for the hypothetical system represented in Figure 6.3. Then estimate the probability of this system being in its ground state.

Prove that the probability of finding an atom in any particular energy level is P(E)=(1/Z)e-F/kT, whereF=E-TS and the "'entropy" of a level is k times the logarithm of the number of degenerate states for that level.

In the numerical example in the text, I calculated only the ratio of the probabilities of a hydrogen atom being in two different states. At such a low temperature the absolute probability of being in a first excited state is essentially the same as the relative probability compared to the ground state. Proving this rigorously, however, is a bit problematic, because a hydrogen atom has infinitely many states.

(a) Estimate the partition function for a hydrogen atom at 5800 K, by adding the Boltzmann factors for all the states shown explicitly in Figure 6.2. (For simplicity you may wish to take the ground state energy to be zero, and shift the other energies according!y.)

(b) Show that if all bound states are included in the sum, then the partition function of a hydrogen atom is infinite, at any nonzero temperature. (See Appendix A for the full energy level structure of a hydrogen atom.)

(c) When a hydrogen atom is in energy level n, the approximate radius of the electron wavefunction is a0n2, where ao is the Bohr radius, about 5 x 10-11 m. Going back to equation 6.3, argue that the PdV term is Tot negligible for the very high-n states, and therefore that the result of part (a), not that of part (b), gives the physically relevant partition function for this problem. Discuss.

See all solutions

Recommended explanations on Physics Textbooks

View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.