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HEAT. Thermal energy The kinetic and potential energy of the random microscopic motion of molecules , atoms , ions, electrons & other particles Heat The thermal energy transferred from a hotter body to a colder body. c alorie (cal) Unit of heat

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Heat

HEAT


Heat

  • Thermal energy

    • The kinetic and potentialenergy of the randommicroscopic motion of molecules, atoms, ions, electrons & otherparticles

  • Heat

    • The thermal energytransferred

      from a hotter body to a colder body

  • .


Heat

  • calorie (cal)

    • Unit of heat

    • The amount of heatneeded to raise the temperature of 1 gram of water 1⁰ C

      1 kcal = 1000 cal = 1 (food) Calorie

  • British Thermal Unit (BTU)

    • The thermal energytransferred

      from a hotter body to a colder body

      1 BTU = 0.252kcal

  • .


Heat

Q = mcΔT


Heat

  • example

    You mix 1.0kg water at 80⁰C with 1.0 kg water at 20⁰C. Whatis the final temperature

    Q = mcΔT Q80⁰C = Q20⁰C

    (mcΔT) 80⁰C = (mcΔT)20⁰C

    (1.0kg)(4187J/kg· ⁰C)(80-T) = (1.0kg)(4187J/kg· ⁰C)(T-20)

    334960 – 4187 T = 4187 T – 83740

    8374 T = 418700

    T = 50⁰C


Heat

  • Mechanicalequivalent of heat

    • The conversion factor between calories and joules

      1 cal = 4.187J

    • You need to convert thermal energy in calories to joules to relate to kineticenergy(1/2 mv2) or potentialenergy(mgy)

  • .


Heat

  • Thermal expansion

    • Expandingsolidsmaintain original shape

    • Expandingliquidsconform to the container

  • Linearexpansion

    ΔL = αLΔTL = length

    α = coefficient of liner expansion

    ΔT = temperature change


Heat

Example:

The highest tower in the world is the steel radio mast of Warsaw Radio in Poland, which has a height if 646m. How much does its height increase between a cold winter day when the temperature is -35⁰C and a hot summer day when the temperature is +35 ⁰C ?

ΔL = αLΔT

= 12x10-6/ ⁰C x 646 x 70⁰C

= 0.54m


Heat

  • Volume expansion

    ΔV= βVΔTL = length

    β = coefficient of liner expansion

    ΔT = temperature change

    coldhot

    Β = 3 α


Heat

  • convection

    • Heatisstored in a movingfluid and iscarriedfrom one place to another by the motion of thisfluid

  • radiation

    ΔL = αLΔTL = length

    α = coefficient of liner expansion

    ΔT = temperature change


Heat

  • radiation

    • The heatiscarriedfrom one place to another by electromagneticwaves

RADIATION


Heat

  • SpecificHeat of a Gas

    MolarSpecificHeatat a constant volume

    the heatabsorbedduring the change of state

    Q = nCvΔTQ = amount of heat required

    n = number of moles

    Cv = specific heat at a constant volume

    ΔT = Change in temperature

    MolarSpecificHeatat a constant pressure

    the heatabsorbedduring the change of state

    Q = nCpΔTCp= specific heat at a constant pressure


Heat

  • Q = nCv ΔT

  • with a small amount of heat, the energy must match

  • dQ = dE so nCv ΔT = dE

  • The force of the gas on the piston is pA and the work done by the gas is dW = Fdx

  • so dW = pAdx Adx is the small change dV of volume

  • dW = pdV

  • dQ = dE+ dW = dE + pdV or nCp dT = dE +pdV

  • nCp dT = nCV dT + pdV Ideal gas Law pdV = nRdT

  • nCp dT = nCV dT + nRdTCp = CV + R

  • R = 8.31 J/K·mol or 1.99 cal/K·mol


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