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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 What is the difference between an atomic and molecular substance? Atomic single atom He Ar Fe Molecular multiple atoms N2 CO2 C6H12 Describe the types of motion • Translational whole atom or molecule changes its location in three dimensional space • Rotational Motion of whole molecule whole molecule spins around an axis in three dimensional space • Vibrational Motion within molecule motion that changes the shape of the molecule – stretching, bending, and rotation of bonds 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 Types of Motion and the States of Matter Matter State Gas Liquid Solid Type Mode Translation Rotation Vibration Atomic Yes No No Molecular Yes Yes Yes Atomic Yes No No Molecular Yes Yes Yes Atomic No No Yes Molecular No No Yes Types of Vibrations Vibration Minimum How atoms number of are atoms connected What changes? Stretching 2 Bond length Bending 3 Bond angle 4 Torsion angle Internal rotation 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. Describe all the modes of vibration in each of the molecules. N2 stretching only CO2 stretching, both symmetric and asymmetric, and bending C4H10 stretching, bending, and internal rotation Which molecule has the highest entropy? What hinders internal rotation in 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! Twisting vibration around double bond in ethene, C2H4 Click to view a movie of the vibration Two methyl groups (-CH3) on biphenyl Chime Guide Click to view Chime structure of lowest energy state Restricted internal rotation or twisting vibration in ring C6H12 Click here for Chime structure – you will need to right click on the Chime structure and click on animation 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 Molecules in solid CO2 – note the tight packing of molecules How would larger molecules ever move around? Chime structure Hexane, C6H12, in the solid state – note the straight chain arrangement of the molecules Spacefilled From: Roland Boese per. comm. Does the phase make a difference in biphenyl? solid Both rings in the same plane Chime structure gas 40o angle between rings still allows pi clouds to interact Chime structure What is the cause of the entropy of solid carbon monoxide? Vibrations and arrangement of the molecules of CO 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. 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. 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