ThermodynamicsTuesday, February 26, 20139:49 AM

Agenda: Check-In

o We will use worksheet from Friday to guide today's class

Prayer Thermodynamics

o Brownian Motiono Temperatureo Heato Gas Laws - quick reviewo Kinetic Theoryo Internal Energy

o 1st & 2nd Law of Thermodynamics

Closureo Bridge project

presentations. How are they coming along?

 

Atomic Theory - all matter made of atoms

Brownian motion - is the seemingly random movement of particles suspended in a fluid (i.e. a liquid such as water or air)

or the mathematical model used to describe such random movements, often called particle theory.

Temperature (T)

the degree of hotness or coldness of a body or environment (corresponding to its molecular activity)

The measure of the average energy of motion, or kinetic energy, of particles in matter. When particles of matter,

whether in solids, liquids, gases, or elementary plasmas, move faster or have greater mass, they carry more kinetic energy, and the material appears warmer than a material with slower or less massive particles.

Is used as a measure of the internal energy or enthalpy, that is the level of elementary motion giving rise to heat transfer.

Heat (Q) energy transferred from one

object to another because of a difference in temperature

The process of energy transfer from one body or system due to thermal contact, which in turn is defined as an energy transfer to a body in any other way than due to work performed on the body.

Energy transfer by heat can occur between objects by radiation, conduction, and convection.

Gas Laws

Combined Gas Law PV = Constant

TSTP?

Ideal Gas Law 

PV = nRTn = number of moles

 R = universal gas constantR = 8.314 J/(mol k)

or 0.0821 (L atm)/(mol K)or 1.99 calories/(mol K)

 

In terms of Avogadro's number

NA = 6.02 x 1023 mol-1

 PV = nRT

where n = N/NA

N = number of molecules

 PV = (N/NA)RT

where k = R/NA

k = Boltzmann's Constant

k = 1.38 x 10-23 J/K

PV = NkT =nRT

  

Kinetic Theory - the theory that gases are made up of a large number of small particles (atoms or molecules), all of which are in constant, random motion. 

KE = (1/2)mv2 = (3/2)kT 

The average translational kinetic energy of molecules in random motion in an ideal gas is directly proportional to the absolute temperature of the gas.

 

Heat (Q) - like work, represents energy transferred from one object to another because of a difference in temperature

Mechanical Equivalent of Heat

Work Done = Heat Input 4.186 J = 1 calorie

Internal Energy - sum total of all the energy of all the molecules in an object

Internal Energy (U)ΔU = (3/2)nRΔT

Difference between Temperature, Heat and Internal Energy

Using Kinetic Theory Temperature - measure

of kinetic energy of individual molecules

Internal Energy - total energy of all the molecules in the object

Heat - transfer of energy from one object to another because a difference of temperature

First Law of Thermodynamics - an expression of the principle

of conservation of energy, states that energy can be transformed (changed from one form to another), but cannot be created or destroyed.

ΔU = Q -Wwhere

U = Internal EnergyQ = HeatW = Work

 Heat in is positive (gain)

Heat out is negative (loss)  

Work on system is negative (in)Work by system is postive (out)

 

Isothermal Process - is a change of a system, in which the temperature remains constant: ΔT = 0. Assume : o gas in contact with a heat

reservoir

o Expansion and compression done very slowly

Gas initially at point A and Q is added

Pressure and volume will change

To keep T constant, V becomes larger and does W

Gas ends at point B Since:ΔU = (3/2)nRΔT = Q -W and ΔT = 0 then Q -W = 0

 Q = W

Q in ( positive)W out (positive)

 

Adiabatic Processo No Q allowed to flow into or

out of the system Q = 0

o Possible for well insulated systems or when process happens very quickly

Internal combustion engine

Therefore:

ΔU = Q -Wsince Q = 0 then ΔU = -W 

If W in, increase U ΔU = (3/2)nRΔT 

Then T also increases &

 P1V1 = P2V2

T1 T2

 

V1>V2 W out, decrease U & T

P1V1 = P2V2

T1 T2 V1<V2

 

Isobarico Constant pressure

 

Change in volume results in work (+ or -)

W = P Δ V ΔU = Q -W = Q - PΔV

 

Isovolumetrico Constant Volume

 

Since V = constant, W = 0 ΔU = Q - W

then ΔU = Q 

Second Law of Thermodynamcisis an expression of the universal principle of entropy, stating that the entropy of an isolated system which is not in equilibrium will tend to increase over time. Entropy is a measure of how organized or disorganized a system is 

A heat engine is a physical device that converts thermal energy to mechanical output. The mechanical output is called work, and the thermal energy input is called heat.

Examples of everyday heat engines include the steam engine, diesel engine, and the gasoline engine. A common toy that is also a heat engine is a drinking bird. All of these familiar heat engines are powered

by the expansion of heated gases. The general surroundings are the heat sink, providing relatively cool gases which, when heated, expand rapidly to drive the mechanical motion of the engine.

                   

 

Carnot Cycle

A heat pump is a machine or device that moves heat from one location (the 'source') to another location (the 'sink' or 'heat sink') using mechanical work. Most heat pump technology moves heat from a low temperature heat source to a higher temperature heat sink. Common examples are food

refrigerators and freezers, air conditioners.