Physics 154 Thermodynamics (and Temperature, Kinetic Theory of gases)

Heat

The energy exchanged between objects when there is a temperature difference, transferred in thermal contact.

calorie

Energy required to raise the temperature of 1 g of water by 1°C

Calorie

Describes energy content in good and is related to the calorie.

Number of calories in a Calorie

1000 calories=1 Calorie

1 Cal=1 kcal

thermal equilibrium

When two systems are in thermal contact but there is no net exchange of energy . Temperature is the same

Zeroth law of thermodynamics

If objects A and B are separately in thermal equilibrium with C. Then a and B are in thermal equilibrium with each other

• Objects are in equilibrium with eachother when they are the same temperature

absolute 0

O Kelvin

The lowest possible temperature achieveable

Kelvin temperature depend on

Waters triple point, where ice, water, and ice temp and pressure coexist within one another.

Is 273.15 K

Linear expansion and units

One dimension of a solid increases (heated bar getting longer)

L is in meters, temperature change is in °C and alpha is 1/°C

area expansion and it’s units

A is in m², T is in °C, alpha (coefficient of linear expansion) is in 1/°C

volume expansion units

V is in m³, T is in °C, beta is 1/°C

Beta equals 3 x linear coefficient

specific heat. Units

The energy Q transferred to a mass will change its temperature by deltaT

J/kg•°C

If temperature change is greater then 0, or Q is greater than 0

Energy flows into the system

If change in temperature is less then 0 and Q is less then 0

Energy flows out of the system

Calorimeter

An insulated container that prohibits heat transfer to the outside environment (thermos, cooler, used to measure heat capacities of unknown substances)

Calorimetry

The qualitative measure of heat exchange

Condensation

Gas to liquid or gas to solid

Sublimation

Solid to gas (dry ice)

What changes during a phase change?

Internal energy. Temperature will stay the same

Phase change completion

When all the matter changes, temperature can change again

Latent heat

The energy Q required to change the phase of a material of mass m

Variable:L

Units: J/kg

Latent heat of fusion

Lf, used in changes between solid and liquid phases

Latent heat of vaporization

Lv, used for changes between the liquid and gas phases

Conduction

Process whereby heat is transferred directly through a material, without any bulk motion of the material

Thermal conductors

Objects that conduct heat well (metals)

Thermal Insulators

Objects that conduct heat poorly (wood, plastic, rubber)

Methods of conduction

Atoms move faster in hot part versus cool part

Heat is transferred through atom collision

Electrons in metals wander and can bring in energy

Dependents of conduction

Time , temperature difference (Th-Tc) in °C, cross sectional area (A), lengh (d in meters)

Convection

The process by which heat is carried from place to place by the bulk movement of a fluid or gas.

Radiation

The process in which energy is transferred by means of electromagnetic waves (light)

Black body object

Perfect absorbers and perfect emitters.

Emissivity

Number between 0 and 1. Ratio of what an object radiates or what it radiates. 1 being better

Law of Radiation (Stefan-Boltzmann)

The power radiated by an object depends on energy Q by object with known temperature, surface area A and emissivity e

Thermodynamics

Branch of physics that describes how the work done on or by an object is related to the transfer of heat between the object and its environment

Compression

Work done on the gas (positive)

Change in volume is less than 0

-Piston

Expansion

Work done by the gas (negative)

Change of volume is more then 0

Q

Energy exchanged between the system and the environment

W

Work done in it by a gas

Positive work on a system

Increased energy

Negative work on a system

Decreases energy of the system

Quasi-static process

Occurs slowly enough that a uniform pressure and temperature exists throughout the whole system at all times

Isobaric

Constant pressure

Work done on the gas

Internal energy change=nCv(deltaT), Q=nCp(deltaT), Work=-PdeltaV

Cp for monatomic gas

5/2R

Adiabatic

No heat transfer , Q=0, Internal energy=W

Internal energy change=nCv(deltaT)

Adiabatic expansion

Does negative work on the system and internal energy decreases

Adiabatic compression

Does positive work on the system and internal energy increases

Isotherm

Constant temperature line

Occurs constant n and T

Adiabatic process

Constant temperature line

Occurs constant n and T

Isovolumetric/ Isochloric

Constant volume

No work ; W=0

Internal energy change=nCv(deltaT)

Q= Internal energy

Isothermal

Constant temperature

If system expands, it loses energy to do work on environment. If compresses, gains energy from work done by the environment

Internal energy=0, Q=-W

Heat engine

Any device that uses heat to perform work and has a hot reservoir, part of input hear used to do work , and remaining heat is expelled to a cold reservoir

Thermal efficiency

tells how much input heat can be converted into work during one cycle

e=1 equals 100% efficient

Area under PV curve

Work

Refrigeration process

Work must be done to extract heat from a cold reservoir and dumb into hot

Coefficient of performance

Rates quality of refrigerator or AC. Higher when heat (Qc) can be extracted without doing much work

Kp

Rates quality of heat pump . Large when heat can be transferred to hot reservoir without doing much work

1st law of thermodynamics

Total energy equal

Second law of thermodynamics

Entropy of isolated system increases.

Spontaneous heat flow is an irreversible process

Carnot engine

Idealized maximum efficiency engines

Carnot cycle

Reversible , Efficent thermodynamic engines follow this

Entropy

Measure of disorder of a system

Ideal gas

Atoms in the gas move randomly

Atoms don’t exert long range forces on one another

Atoms only interact with one another and their container through elastic collisions

Each particle is point-like (negligible volume)

Mole

1 mole of any substance as many particles as there are atoms

Avogadros number

Number of atoms per mole

(1 mole of ANYTHING contains Na particles

STP

1 atm and 273 K

Absolute pressure unit

Pa

Volume unit in ideal gas law

m³

Gay-Lussacs Law

n and V are constant

Charles Law

n and P are constant

Boyles Law

n and T are constant

Van der Waals equation of state

More accurately depicts P, V, and T relation of an gas

Increase volume in an ideal gas, decrease ____

Pressure

Van der waals gases PV diagram

Isotherms with more interesting shapes, high temperature (hyperbolic), critical temperature (curve develops plateau), lower temps (increasing the volume increases the pressure-Un physical-represents a phase transition-holds at a constant pressure)

A single gas particle does not have a temperature. True or False

True

Root mass square speed

Average speed of gas molecule

Internal energy

Sum of various kinds of energy that the atoms or molecules possess

Monatomic gas

A gas composed a single type of only, which only has translational (linear) motion

Mean free path

Average distance a molecule will travel before it experiences a collision (lamda)

Mean free time

Average time a molecule will travel before it experiences a collision

Cv of monotomic gas

3/2R

Equipartition Theorem

The energy of any ideal gas in thermal equilibrium is split among it degrees of freedom

Molar heat capacity

Q=nCvdeltaT