Chemistry 141, Chapter 2 notes
Chemistry 141, Chapter 2 notes Chemistry 141
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This 2 page Class Notes was uploaded by Sara Auger on Monday October 17, 2016. The Class Notes belongs to Chemistry 141 at Emory University taught by Dr. Egap in Fall 2016. Since its upload, it has received 7 views. For similar materials see Chemistry 141 in Chemistry at Emory University.
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Date Created: 10/17/16
Chapter T wo: Measurement, Problem Solving, and the Mole Concept Thursday, September 1, 2016 8:40 PM 2.1: "The Metric Mix-Up: A $125 Million Unit Error" Basically a mars weather monitor failed because they mixed up units. Units are critical 2.2: "The Reliability of Measurement" Reliability depends on the instrument used to measure More digits in measurement = more reliability o Scientists do this on purpose to reflect reliability of instrument o Uncertainty is in the last recorded digit (+/- 1) Accuracy: how close the measured value is to the actual value Precision: how close the measured values are to each other or how reproducible they are Random Error: error that has equal probability of being too high or low o Averages out with repeated trials Systematic error: tends to be either too high or too low o Doesn't average out. 2.3: "Density" Density of a substance is the ratio of its mass to its volume (density=mass/volume) o A physical property of a substance o Depends on the temperature of the substance o An intensive property: independent of the amount of the substance Mass, for example, in an extensive property (depends on the amount of the substance. Only knowing something's mass doesn't identify it.) 2.4: "Energy and Its Units" Two fundamental components of our universe are matter and energy Energy: the capacity to do work o Work: the action of a force through a distance o Total Energy: a sum of its kinetic energy (the energy associated with motion) and potential energy (associated with its position or composition) Ex: If a weight falls, potential energy is converted to kinetic as it gets closer to the ground. When it hits the ground, kinetic energy is converted primarily to thermal energy (energy associated with the temperature of an object) kg x 1/2mv2 o Energy is neither created nor destroyed. (Law of Conservation of Energy) o Systems with high potential energy ten to change in a way that lowers potential energy. Objects or systems with high potential energy tend to be unstable. Ex: molecules the compose gasoline have a relatively high potential energy. As the energy of the molecules is released some of it can be put to work (like moving a car) Chemical potential energy arises primarily from electrostatic forces between the protons and electrons in the atoms. o The SI unit of energy kg x m2/s2 or Joules After James Joule (English, 1818-1889) Another common unit is calorie: the amount of energy required to raise the temperature of water by 1 degree Celsius. 1 Cal = 4.184 J Related: food calorie [C] equals 1000 [c] Another larger unit: kilowatt-hour (what bills are based off) o Energy can be transferred from a system to surroundings: anything the system interacts with. o Chemical processes almost always include an energy change o Exothermic: system loses energy, change in energy is negative. o Endothermic: system gains energy, change in energy is positive. 2.5: "Quantifying Changes in Energy" Dimensional Analysis: using units as a guide to solving problems o Include units in your calculations; multiply, divide, and cancel them like anything else. You'll be left with final unit o Conversion factor: a fractional quantity with the units we are converting from on the bottom and the units we are converting to on top. 2.6: "Problem-Solving Strategies" Identify Given Identify Endpoint Make a plan to get from first to second Order of magnitude Estimation: focus only on the exponential part of a number written in scientific notation. (See page 49) o Left with powers of 10 2.7: "Solving Problems Involving Equations" They show relationships… not a lot here tbh 2.8: "Atoms and the Mole: How Many Particles" All matter is ultimately particulate and countable When samples of matter interact, they interact particle by particle We use the mole to count "how many" o Amount of material containing 6.022x10 to the 23 particles o Named Avagadro's Number o The mass of 1 mol of something is its molar mass