U7 Thermodynamics

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28 Terms

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Matter
Exists in solid, liquid, and gas
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Solid
ā†’IMF keep molecules in fixed, crystalline structure

ā†’fixed shape and volume

ā†’Molecules vibrate but donā€™t move
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Liquid
ā†’IMF are weaker, molecules slide past each other

ā†’no fixed shape, fixed volume
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Gas
ā†’Molecules free to move with (IDEALLY) no force between them

ā†’No fixed shape/volume (expand to fill available space)
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Amount of substance can be measured in:
mass \[kg\]

volume \[1cm^3\]

number of particles \[1 mol/6\*10^23\]
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Density of a substance
mass per unit volume

p=m/v
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Molar Mass
Mass of 1 mole of substance
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Internal Energy
Total Potential and Kinetic Energy of the particles
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Temperature
measure of the average Kinetic Energy
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Thermal Equilibrium
Once two objects reach the same temperature in which no heat will flow
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Specific Heat
Q=mcĪ”T

Qā†’Heat transferred

mā†’Mass

cā†’Specific Heat (will be a constant)

Tā†’Temperature

\
\*\*-Q=Q

Heat Lost=Heat gained between two objects
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With a car, why could the actual temp be less than predicted?
Some energy lost to the environment

Internal friction between tires/road

Air resistance

Brakes cooled by convection
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Methods of Heat Transfer

1. Conduction: Materials in direct contact
2. Convection: Motion of a fluid
3. Radiation: An object will radiate energy and absorb energy as the environment (as electromagnetic radiation)
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Ideal Gas Assumptions

1. Large number of identical molecules
2. Volume of molecules is negligible (most is empty space)
3. Constant, random motion
4. No IMFS (0 potential energy, all kinetic)
5. All collisions are elastic (momentum and kinetic energy conserved)
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Ideal Gas Law
PV=nRT

Pā†’ Pressure \[N/m^2 or Pa\]

Vā†’ Volume \[L\]

nā†’ moles \[integer\]

Rā†’ gas constant \[J/k mol\]

Tā†’ Temperature \[K\]
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Boyleā€™s Law
Pressure and Volume are inversely proportional
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Chareerā€™s Law
Volume and Temperature are directly proportional
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Amontonā€™s Law
Pressure and Temperature are directly proportional
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Average Kinetic
EK=3/2KbT

EK=m/2v^2

EKā†’ Avg Kinetic Energy \[J\]

Kbā†’ Boltzmannā€™s Constant \[1.38\*10^-23\]

Tā†’ Absolute Temperature \[K\]
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Why can we use average Kinetic energy formula to determine the Total Internal Energy?
There is no potential energy in an ideal gas
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Root Mean Square Speed
Average velocity of all particles of ideal gas is 0

rms=āˆš3RT/m

Rā†’ Gas Constant

Tā†’ Temperature

mā†’ molar mass \[Kg/mol\]
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Real gases behave like ideal gases whenā€¦
High temperatures and low pressure
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Radiation
Energy that is transferred as waves such as visible light and infrared. Can travel through a vacuum
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Black Body Radiator
Object that is perfectly opaque and absorbs all energy. It does not reflect or transmit radiation.

Good absorber = Good emitter

Black body Radiator is a perfect absorber, best possible emitter

(Theoretical, closest approximation is a star)
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Emissivity - e
ratio of power radiated by surface

solar power radiated by a black body radiator of the same temperature/area used to adjust for an object that isnā€™t a perfect black body radiator between 0
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Stefan-Boltzman Law
P=eĻƒAT^4

Pā†’ Power \[W\]

eā†’ emssivity

Ļƒā†’ Stefan-Boltzman Constant \[5.67\*10^-8\]

Aā†’ Surface Area (REMEMBER 4Ļ€r^2) \[m^2\]

Tā†’ Absolute Temperature \[K\]
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Radiated Energy
Black body radiator heated up ā†’ emit range of different wavelength

intensity and wavelength distribution of emitted waves

depends on temperature of the body
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Wienā€™s Displacement Law
Black body radiator curve for different temperatures peak at a wavelength inversely proportional

Ī»=2.9\*10-2/T

Ī»ā†’ Wavelength \[m\]

Tā†’ Temperature \[K\]