Thermochemistry_Book Notes.docx

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University of Minnesota Twin Cities
CHEM 1061
Hyunjoo Im

Book Notes 6.1 Energy  Read appendix B (A10)  Potential Energy: capacity to do work; objects that can do work either b/c of their composition or b/c of their location have potential energy  Kinetic Energy: moving objects possess this  Ex: water behind dam: stored = potential energy; when pipe opened, some potential energy = converted to kinetic energy use water to turn blades of generator  potential energy from beginning electrical work 2 2  E k ½mv ; m = mass, v = speed in meters per second; units of energy = kg * (m/s) = kg m s -2 2 -2 o 1 joule (J) = 1 kg m s ; joule = SI unit of energy o 60 watt lightbulb uses 60J per second  1W = 1J/s???  Work = force * distance; force required to change speed of object (to make it accelerate) o 1 newton of force imparts on acceleration of one meter per second per second to a 1-kg object -2 o Force = 1kg * 1ms = 1 newton (N) o Work = 1N * 1m = 1 kg m s = 1J work has same unit as energy  Ex: tennis ball bouncing: ball raised energy to do that stored as potential energy o Ball released some potential energy converts to kinetic energy o Kinetic energy reaches max when hits ground o Rebounds kinetic energy ↓ (ball slows down), potential energy ↑ (ball rises) o If perfectly elastic, ball would rebound w/ same energy, continue bouncing forever. o But ball height decreases b/c some kinetic energy goes into atoms of ball, ground, surrounding air  temperature increase o Energy on macroscopic level changes to energy on microscopic level 6.2 Thermochemistry: Some Basic Terms  Thermochemistry: study of energy changes that occur during physical processes and chemical rxns (reactions) (branch of broader study thermodynamics: relationship btwn heat and work)  Say 2 things exchange energy (not one thing loses/gains energy)  System and Surroundings o System = part of universe we’re studying o Surroundings = rest of universe (but we can limit to those that interact w/ system) o Interactions refer to exchange in energy/matter/both in system & surroundings o 3 types of systems  Open system: can exchange matter/energy/both w/ surroundings  Closed system: may exchange energy, but not matter w/ surroundings  Isolated system: exchanges neither energy nor matte
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