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Meeting%2015%202010

# Meeting%2015%202010 - Meeting 15 Chapter 6 Thermochemistry...

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1 Meeting 15 Chapter 6- Thermochemistry Thermochemistry: study of energy changes during chemical reactions We will distinguish between kinetic energy, KE ( energy of motion ) and potential energy, PE ( energy of position ). KE KE of water behind dam is converted into PE as it falls in the Earth’s gravitational field. The water also does useful work by turning turbines to make electrical energy.

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2 A bouncing tennis ball illustrates the interconversion of PE and KE. Q: when is the PE at a maximum in each bounce? What causes successive bounces to be lower in height? PE and KE - SI units Potential Energy in a gravitational field PE = mgh m = mass (kg) g = gravity constant (m s 2 ) h = height (m)
3 units for PE are kg m 2 s 2 J KE = (1/2) mv 2 m = mass (kg); v = velocity (m s 1 ); v 2 = (m 2 s 2 ) Units: units are kg m 2 s 2 J Watt = 1 Js -1 , unit of power Power is the rate at which work is performed A 60 W light bulb uses 6O J sec -1 of energy. Work A force acting through a distance W = f x d. SI unit (Joule) W = m x a x d = energy Notice that work has units of energy What is thermochemistry ? Chemical equations and stoichiometry tell us what reacts and how much reacts There is more to chemical reactions Some reactions release energy (exothermic) Some reactions require energy(endothermic)

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