# HEAT - PowerPoint PPT Presentation

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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

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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

• .

• 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

• .

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)

• .

• 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

ΔL = αLΔTL = length

α = coefficient of liner expansion

ΔT = temperature change

• The heatiscarriedfrom one place to another by electromagneticwaves

• 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