Matter, Motion, and Entropy: A Review

1. Matter, Motion, and Entropy: A Review Answers will appear as you click. This is set up as a slide show so it will not print. CHM 102 Sinex

2. What is the difference between an atomic and molecular substance? Atomic single atom He Ar Fe Molecular multiple atoms N2 CO2 C6H12

3. Describe the types of motion • Translational • Rotational • Vibrational whole atom or molecule changes its location in three dimensional space Motion of whole molecule whole molecule spins around an axis in three dimensional space  Motion within molecule motion that changes the shape of the molecule – stretching, bending, and rotation of bonds

4. Which type of motion contributes the most to the entropy of a substance? Translational motion Which type of motion is the cause of collisions? Translational motion Which type of motion influences the orientation for an effective collision? Rotational motion

5. Types of Motion and the States of Matter

6. Types of Vibrations

7. In solids such as the carbon tetrahedron from the diamond structure, how would you describe the motion of the atoms? As the carbon atoms vibrate, all the bond lengths vary about an average value.

8. Describe all the modes of vibration in each of the molecules. N2 stretching only stretching, both symmetric and asymmetric, and bending CO2 C4H10 stretching, bending, and internal rotation Which molecule has the highest entropy?

9. What hinders internal rotationin a molecule? • Double or triple bonds • Bulky groups in certain positions on some molecules • Ring formation - cyclic molecules • Sometimes hybrid orbitals (lone pairs of electrons) on single bonds such as hydrogen peroxide • Molecules bound in a crystalline solid Examples are shown on the following three sides!

10. Twisting vibration around double bond in ethene, C2H4 Click to view a movie of the vibration Two methyl groups (-CH3) on biphenyl Click to view Chime structure of lowest energy state Chime Guide

11. Restricted internal rotation or twisting vibration in ring Click here for Chime structure – you will need to right click on the Chime structure and click on animation C6H12 Hydrogen peroxide, twisting motion along single bond Click here for Chime structure – you will need to right click on the Chime structure and click on animation H2O2 has a permanent dipole moment m = 2.0 D

12. Hexane, C6H12, in the solid state – note the straight chain arrangement of the molecules Space- filled From: Roland Boese per. comm. Molecules in solid CO2 – note the tight packing of molecules How would larger molecules ever move around? Chime structure

13. Does the phase make a difference in biphenyl? solid gas Both rings in the same plane 40o angle between rings still allows pi clouds to interact Chime structure Chime structure

14. What is the cause of the entropy of solid carbon monoxide? Vibrations and arrangement of the molecules of CO

15. Why do solids have low entropies? Stotal = Strans + Srot + Svib Strans > Srot >> Svib How do impurities in a solid influence the solid’s entropy? Impurities cause an increase in entropy.

16. Here is a crystal of the mineral zircon. Click on the image, and radioactive decay will occur. How does entropy change? ZrSiO4 Source: http://www.esc.cam.ac.uk/movies The decay particle causes a zirconium ion to recoil and it disrupts the structure which slowly recovers. In the end, the crystal structure becomes more disordered or DS > 0.

17. Proteins – long chains of amino acids chain* How does the entropy change as the chain takes the form of a helix? coiling of 10 glycine chain helix* DS < 0 due to limited internal rotation in hydrogen-bonded helix (secondary structure of protein) *Chime structures