Feb 24 Lecture --thermodynamics

using/releasing energy with heat

heat=q

  • exothermic reaction is one where heat is released from a high energy set of reactions

  • if it is exiting it is <0

  • low energy system converting to a high-energy system is endothermic (heat entering the reaction)

  • if it is entering it is >0

forms of energy

  • potential energy-stored energy

    • coiled spring

    • chemical bonds (it’s stored in them)

    • cyclist at the top of a hill

  • kinetic energy-energy in motion

    • cyclist descending hill

    • releasing coiled spring

  • work energy—force acting over a distance

    • work=force X distance

1st law of thermodynamics

  • conversion of energy requires that the total energy change in the system and the surroundings must be 0

    • change energy universe=0=change energy system + change energy surroundings

  • change in energy=energy in final state-initial energy state

    • Efinal>Einitial if energy is entering (+)

    • Efinal<Einitial if energy is leaving (-)

convert among common units of energy

  • Joule (J) is the amount of energy needed to move a 1-kg mass a distance of one meter

    • 1J=1N*m=1Kg*m²/s²

  • calorie (cal) is the amount of energy needed to raise the temp of one gram by 1 deg C

    • Kcal=energy needed to raise 1000 g of water 1 deg C

    • food cal=Kcal

  • energy conversion

    • 1 cal=4.18 J

    • 1 Cal=1000 cal

    • 1 kilowatt-hour(kWh)=3.60X10^6 J

measuring heat entering/leaving

heat is a type of kinetic energy

  • KE=1/2mv²

heat and temp

  • heat is quantified w/ specific heat capacity

    • amount of heat energy required to raise the temp of one gram of a substance 1 deg C

    • Cs

    • units are J/(g*deg C)

  • molar heat capacity is the amount of heat required to raise the temp of one mole of substance 1 deg C

  • q=(m) X (Cs) X(deltaT)

zeroth law of thermodynamics

heat capacity

important equations

  • deltaE=Efinal-Einitial

  • DeltaE=q(heat)+w(work)

  • q=mass of substance X Cs X deltaT

  • w=-pdeltaV

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