U7 Thermodynamics

Matter

Exists in solid, liquid, and gas

Solid

→IMF keep molecules in fixed, crystalline structure

→fixed shape and volume

→Molecules vibrate but don’t move

Liquid

→IMF are weaker, molecules slide past each other

→no fixed shape, fixed volume

Gas

→Molecules free to move with (IDEALLY) no force between them

→No fixed shape/volume (expand to fill available space)

Amount of substance can be measured in:

mass [kg]

volume [1cm^3]

number of particles [1 mol/6*10^23]

Density of a substance

mass per unit volume

p=m/v

Molar Mass

Mass of 1 mole of substance

Internal Energy

Total Potential and Kinetic Energy of the particles

Temperature

measure of the average Kinetic Energy

Thermal Equilibrium

Once two objects reach the same temperature in which no heat will flow

Specific Heat

Q=mcΔT

Q→Heat transferred

m→Mass

c→Specific Heat (will be a constant)

T→Temperature

**-Q=Q

Heat Lost=Heat gained between two objects

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

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)

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)

Ideal Gas Law

PV=nRT

P→ Pressure [N/m^2 or Pa]

V→ Volume [L]

n→ moles [integer]

R→ gas constant [J/k mol]

T→ Temperature [K]

Boyle’s Law

Pressure and Volume are inversely proportional

Chareer’s Law

Volume and Temperature are directly proportional

Amonton’s Law

Pressure and Temperature are directly proportional

Average Kinetic

EK=3/2KbT

EK=m/2v^2

EK→ Avg Kinetic Energy [J]

Kb→ Boltzmann’s Constant [1.38*10^-23]

T→ Absolute Temperature [K]

Why can we use average Kinetic energy formula to determine the Total Internal Energy?

There is no potential energy in an ideal gas

Root Mean Square Speed

Average velocity of all particles of ideal gas is 0

rms=√3RT/m

R→ Gas Constant

T→ Temperature

m→ molar mass [Kg/mol]

Real gases behave like ideal gases when…

High temperatures and low pressure

Radiation

Energy that is transferred as waves such as visible light and infrared. Can travel through a vacuum

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)

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 isn’t a perfect black body radiator between 0<e<1

Sun approx 1

Earth apron .6

Stefan-Boltzman Law

P=eσAT^4

P→ Power [W]

e→ emssivity

σ→ Stefan-Boltzman Constant [5.67*10^-8]

A→ Surface Area (REMEMBER 4πr^2) [m^2]

T→ Absolute Temperature [K]

Radiated Energy

Black body radiator heated up → emit range of different wavelength

intensity and wavelength distribution of emitted waves

depends on temperature of the body

Wien’s Displacement Law

Black body radiator curve for different temperatures peak at a wavelength inversely proportional

λ=2.9*10-2/T

λ→ Wavelength [m]

T→ Temperature [K]