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HEAT

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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

- The thermal energytransferred
- .

- 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

- The thermal energytransferred
- .

Q = mcΔT

- 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

- 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)

- The conversion factor between calories and joules
- .

- Thermal expansion
- Expandingsolidsmaintain original shape
- Expandingliquidsconform to the container

- Linearexpansion
ΔL = αLΔTL = length

α = coefficient of liner expansion

ΔT = temperature change

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

- Volume expansion
ΔV= βVΔTL = length

β = coefficient of liner expansion

ΔT = temperature change

coldhot

Β = 3 α

- 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

- radiation
- The heatiscarriedfrom one place to another by electromagneticwaves

RADIATION

- 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

- 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