PS 100 Chapter 18 & 19 lecture notes
PS 100 Chapter 18 & 19 lecture notes Phy S 100
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This 5 page Class Notes was uploaded by Alisa Pierce on Sunday October 25, 2015. The Class Notes belongs to Phy S 100 at Brigham Young University taught by Professor Hirshmann in Summer 2015. Since its upload, it has received 14 views.
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Date Created: 10/25/15
Physical Science 100 Lecture Notes 1021 amp 1023 Chapter 18 amp 19 Chapter 18 Oct 21 2015 Which aspect of the Molecular Model is most responsible for the movement of molecules 0 Particles are in random motion Diffusion 0 Molecules mix with other molecules 0 A process that wants to spread things out 0 There is not a natural reversal to that process Processes often happen in only one direction There are processes that can go back and forth that most processes only go one way Most processes are irreversible Reversible processes go equally well in either direction 0 Water solid at CC water liquid at 0C Irreversible processes go spontaneously on their on in only one direction may or may not be able to be reversed 0 Ice cube dropped in glass of warm water 0 Water poured on the ground on a very cold day The Second Law of Thermodynamics 0 A reversible process does not change the total amount of disorder in the Universe 0 An irreversible process always increases the total amount of disorder in the universe 0 THE DISORDER ENTROPY OF THE UNIVERSE NEVER DECREASES 0 Refrigerators freezers 0 Warm liquid water transforms to cold ice cubes an entropy decreasing process 0 Heater 0 Increase in entropy from the hot air is bigger than the decrease from water Entropy 0 A measure of quotdisorderquot 0 A measure of the possible number of states or configurations or arrangements a system can be in o Pennies 0 There are a lot of ways you can mix them up but there is only one way they can all be heads 0 Why is it more likely that the pennies will all be quotdisorderedquot rather than all heads or all tails 39 There are many more ways to have them mixed up than there are ways for them to be all one kind 0 Most likely arrangement half heads and half tails 0 A measure of how widely energy is dispersed between different kinds of energy in space 0 Kinetic electrical potential chemical potential gravitational potential heat light 0 The more widely dispersed energy is the more quotdisorder and the more quotentropyquot there is 0 Some are more ordered than others 0 Think about the container with the two molecules Why are the two types of molecules unlikely to ever go back to being in separate halves There are so many ways to mix them that the particular mixing where one kind are on one side and the other kind are on the other side is almost certain never to happen 0 Is it possible that heat could ow from a cold object to a warm object Yes but there is a very small chance Equilibrium 0 When left to themselves all closed systems tend towards a point of maximum disorder called EQUILIBRIUM 0 Once equilibrium is reached no further macroscopic changes occur in the system 0 Is the Universe a closed system Entropy and Direction 0 Heat will ow from hot to cold 0 The most common way to arrange molecules 0 It is possible for the molecules to go the other way but it is not likely 0 If you put work or energy into a system entropy decreases o In a freezer sitting in your kitchen warm liquid water transforms to cold solid ice the entropy of the water decreases o In a freezer sitting in your kitchen warm liquid water transforms to cold solid ice The amount of entropy decrease of the water is less than the amount of entropy increase of the kitchen Ordering 0 Dividing things into quotcompartmentsquot Why are KB and GPE more ordered 0 All of the atoms have the same amount of energy 0 Why is thermal energy the least ordered 0 The atoms are moving in random directions at random speeds Important rule 0 Any form of energy can be converted to a form of energy with more disorder but cannot be totally converted to a form of energy with less disorder Nature extracts a price if you want to transform energy into a quothigherquot form 0 Using quotmidlevelquot Chem PE to get Macroscopic KE a moving car 0 100 efficiency in a car is nearly impossible 0 No quotperpetual motionquot machines Over time the quality of energy degrades 0 Philosophical implications 0 End of the Universe Heat Death 0 Heat always moves from a warmer to a colder body Chapter 19 October 23 Elements vs Compounds 0 Elements only one kind of atom 0 Compounds two or more kinds of atoms 0 If a pure substance has fixed chemical composition Chemical Matter 0 Pure substance 0 Element one kind of atom 0 Compound two or more kinds of atoms Mixtures 0 Alloys solid mixtures of metals 0 Solutions 0 Blendscomposites Atomic molecule example helium atoms Diatomic molecule example Oxygen Network matter regularly repeating organization of multiple atoms Chemical bonds interactions between atoms 0 Atoms in molecules are held together by quotbondsquot A bond usually involves a pair of elections 0 Strong bonds metallic ionic covalent 0 Weak bonds van der Waals Hydrogen 0 In our models we often use sticks to represent bonds and balls to represent atoms How does bonding work 0 Atoms give up obtain or share electrons and in the process combine to form the substances around us 0 This bonding involves only the electrons in the outermost unfilled orbitals the valence electrons All other inner electrons don39t matter as far as bonding is concerned Stability 0 All bonding involves atoms sharing or exchanging electrons in a quotstablequot way 0 Stability means 0 To fall into a lower energy state and thus be more tightly bound 0 To completely fill an orbital set What is a bond 0 When one nucleus is near electrons you get an energy well 0 If more than one nucleus is near you get extra energy wells If one of these extra energy levels is lower than occupied valence levels it is a bonding orbital 0 A bond is a pair of electrons that are in a state orbital which 0 Only exists when one or more atoms are closer together 0 Is lower in energy than the valence orbitals 0 The bond between two atoms represents a lower energy level 0 Energy is released when the bond forms and energy is later required to break the bond Writing Chemical formulas for molecular matter 0 Identify atoms in a molecule 0 Give the number of each type of atom as a subscript 0 For our purposes the order of the atoms doesn t matter 0 Examples 0 H20 0 SS 0 CH4 0 Hydrogen peroxide Bleach and disinfectant 0 Glycine one of the 23 essential amino acids Molecules have shapes 0 Shapes can determine particle properties of the molecule 0 Sticks represent bonds 0 Balls represent atoms The shape of a molecule is determined by molecular orbitals 0 When H2 is formed energy is released as heat 0 So in H2 each electron needs more energy than before to escape 0 H has a different discrete spectrum that H2 Molecules belong to families