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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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Presentation Transcript
slide2
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

  • .
slide3
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

  • .
slide5
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

slide6
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)
  • .
slide7
Thermal expansion
    • Expandingsolidsmaintain original shape
    • Expandingliquidsconform to the container
  • Linearexpansion

ΔL = αLΔT L = length

α = coefficient of liner expansion

ΔT = temperature change

slide8
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

slide9
Volume expansion

ΔV= βVΔT L = length

β = coefficient of liner expansion

ΔT = temperature change

cold hot

Β = 3 α

slide12
convection
    • Heatisstored in a movingfluid and iscarriedfrom one place to another by the motion of thisfluid
  • radiation

ΔL = αLΔT L = length

α = coefficient of liner expansion

ΔT = temperature change

slide13
radiation
    • The heatiscarriedfrom one place to another by electromagneticwaves

RADIATION

slide16
SpecificHeat of a Gas

MolarSpecificHeatat a constant volume

the heatabsorbedduring the change of state

Q = nCvΔT Q = 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 = nCpΔT Cp= specific heat at a constant pressure

slide17
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 + nRdT Cp = CV + R
  • R = 8.31 J/K·mol or 1.99 cal/K·mol
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