Chapter 6

# Chapter 6 - Chapter 6 Thermochemistry Energy Energy = Heat...

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Chapter 6: Thermochemistry 1 Energy Energy = Heat + Work Energy: Kinetic or Potential KE = ½ mv 2 Ex. How much energy does a 2 ton car have going at a speed of 60 mph? 4000 lbs 1kg 2.20 lbs = 1818 kg 60 miles hr 1 hr 1609m 3600s 1 mile = 26.8 m/s E = ½ mv 2 = ½(1818 kg)(26.8 m/s) 2 E = 652880 J or 653 kJ PE = stored energy 1 cal = 4.184 J (exact) 1 Cal = 1000 cal = 1 kcal = 4.184 kJ Conservation of Energy – energy can’t be created or destroyed, only converted from one form to another. swing high PE , low KE high KE , low PE high PE , low KE sum of PE and KE is constant temperature – when something gets hot what is really happening? increasing kinetic energy of particles if water feels cold low KE of water molecules if water feels hot high KE of water molecules heat – transfer of KE from 1 object to another because of temperature difference. if put hot metal bar in cup of water, heat is transferred from bar to water and water gets hot. chemical energy – type of potential energy stored in a chemical compound piece of wood has high chemical energy—can light it on fire and convert it to heat ashes have low chemical energy—can’t burn them (react) and convert to heat (energy)

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Chapter 6: Thermochemistry 2 Internal Energy and State Functions system – reaction or chemical change that is focused on surroundings – other stuff like beaker, air, etc. – stuff surrounding system 1 st Law of Thermodynamics – total internal energy of isolated system is constant in reality, energy will either flow out of system or into system E = E f E i if E = -: energy flowed out of system if E = +: energy flowed into system If energy flows out, final energy state of system is lower than initial If energy flows in, final energy state is higher than initial. Consider the reaction 2H 2 ( g ) + O 2 ( g ) → 2H 2 O( g ) + 484 kJ E = -484 kJ this is because internal energy of H 2 O is less than internal energy of H 2 and O 2 . This makes sense. H 2 and O 2 (mixed) are explosive while H 2 O is not. Likewise if you want to electrolyze H 2 O into H 2 and O 2 , need to provide energy 484 kJ + 2H 2 O( g ) → 2H 2 ( g ) + O 2 ( g ) E = +484kJ Need to put energy in to electrolyze H 2 O into H 2 and O 2 . This makes sense because internal energy of H 2 and O 2 are higher than H 2 O. internal energy is state function
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Chapter 6 - Chapter 6 Thermochemistry Energy Energy = Heat...

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