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Download 1 Increasing order Example: Refrigerator Example: Automobile Why
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Some things that have been bothering a few students: How do you know that the disorder created by digesting your food and sweating is bigger than the order created when you cleaned your room? 1. 1. Increasing order You can increase order in part of a system. When you do, something or some part of the universe becomes even more disorganized so that the total disorder is increased. There is a mathematical definition for entropy…You don’t need to know how to do it, but it is possible to actually calculate out how much the entropy changes. When all changes are taken into account the total entropy always goes up. Examples: Refrigerator Car Engine Example: Refrigerator z Which is more ordered – (A) warm outside and cold inside or (B) all the same temp.? z Compressor and condenser cool down the air inside the fridge. z an ordering process Use highly organized electrical energy which is turned into thermal energy that heats up the room Maxwell’s demon….a little monster that sits and sorts molecules a disordering process Example: Automobile Chemical potential energy in fuel Thermal Energy Macroscopic K.E. + Thermal energy (Hot gases from combustion) combustion) Efficiency = % of input energy which is converted to useful, desired energy. Auto ~25% efficient. For every $1 you spend on gas, get 25 cents of motion. No heat engine is 100% efficient. WHY? Which is greater? Why is that? What is highest in the energy hierarchy? Can you convert 100% of CPE into KE? Can you convert 100% of CPE into heat? How does the car get KE out of thermal energy? Some of the energy is “wasted” heating up the environment. The Gospel Gives a More Optimistic View “If you picked up a watch far from human habitation and found it running, you would ask not only ‘Who made this watch?’ watch?’ but ‘Who wound it up?’ up?’ So it is with the universe. The universe is running down… down… In a very real sense, then, the universe is like a clock that has been wound up. If it is selfself-winding, it is unique in scientific experience.” experience.” -Henry Eyring Reflections of a Scientist, pp. 75-76 1 Chapter 19: Welcome to chemistry Have you done your reading for today? A. B. Lots of definitions: Make sure you know the terms Most to all Less than ½ to none Which of the materials below is atomic matter? Water, H2O, is: A. A. Carbon monoxide B. NaCl B. C. C. Copper D. Helium Element Compound Mixture Solution Alloy Atomic matter Molecular matter Network solid Chemical Bond D. An element A compound Atomic matter Network matter E. Oxygen In what chemical form do pure materials exist? Atoms vs Molecules vs Network Materials Atomic – individual atoms not bound to any others (RARE— (RARE—e.g., noble gases) Molecular – two or more atoms joined together as single unit How does this relate to properties from Chapter 12? What type of matter had the lowest melting points? What type of matter had the highest melting points? Network – atoms stacked in crystal 2 What is a bond? etc What is a bond? When one nucleus is near electrons, you get an energy well. If more than one nucleus is near, you get extra energy levels… If one of these extra energy levels is lower than occupied valence levels, it is a bonding orbital. A bond is a pair of electrons that are in a state (orbital) which 1. 2. Only exists when one or more atoms are closer together Is lower in energy than the valence orbitals for the individual atoms This means you’d have to put energy in to move the atoms back apart….The atoms are “bound” together. BOND Notation: Counting atoms The number of atoms bound in a molecule is given by the subscript The number of copies of a molecule is written in front of the molecule If the grey atom is C (carbon) and the white H (hydrogen), what is the chemical formula? a) b) c) O atom d) e) HC H4C CH4 CH4 CH4 H atom H atom H2O What’s the chemical formula? Chemical Formulas Network Matter 1) Identify kinds of atoms 2) Give the relative number of each atom type metallic magnesium Quartz silicon dioxide O Mg Si SiO2 Sodium chloride Hydrogen peroxide Glycine Bleach and disinfectant One of the 23 essential amino acids 3H2O2 NH2CH2COOH or Na Cl NaCl 3 Molecules have shapes CH4 Molecules belong to families What elements are present? CH4 9 Atoms always connected in same pattern CH3CH2CH3 (or C3H8) How are the H atoms arranged around the central C atom? C8H18 Formulas? What other molecules might belong to this family? fuels Tetrahedron four triangular faces CH3CO2H Formulas? How do we know how molecules are put together? CH3(CH2)10CO2H What groups of atoms are common to all three molecules? Mass Spectrometry IR spectrometry CH3 CH2 CO2H CH3(CH2)14CO2H family of organic acids all three are in foods we eat Chemical Formulas & Structures by Weighing Molecules Masses of molecular fragments Chemical Formula & Structure From Interaction with IR Light Mass Spectrometry Vibrational Spectroscopy fingerprint region C9O4H8 Aspirin C9O4H8 Aspirin Parent peak: Mass of the molecule 180 amu C=O Energies of vibrations Molecular groups vibrate in different regions 4
