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ThermodynamicsThermochemistry y

Chem 211

Ahmad Mahmoud Mohammad Alakraa, Ph.D.

Professor of Physical ChemistryProfessor of Physical Chemistryamahmoud@sci.cu.edu.eg

http://scholar.cu.edu.eg/?q=ammohammad/classes/

Office Hours:    Mondays 10:00 – 12:00   Tuesdays 12:00‐2:00 

Chemistry New Building ‐ 1st Floor

Creditالصفة معتمده ت ع ن متطلب اسم المقرر رمز

المقرر

إجباري 3 0 3 2 102ك الديناميكية الحرارية الكيميائية 211ك

References

1) Thermodynamics: an engineering approach, 8th edition, Yunus A.Çengel and Michael A. Boles, 2015, McGraw‐Hill Education.

2) Chemistry: An Atoms First Approach, Steven S. Zumdahl andSusan A. Zumdahl, 2012, Brooks Cole, a part of CengageLearning.

3) Chem 211 Note from the Department of Chemistry

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Assessment

A 2h unseen written examination carries 60% of the totalmark

Mid term Exam. carries 10% of the total mark.b k f h l k Lab work carries 30 % of the total mark.

Passing CriteriaPassing Criteria 60% for the total course mark

Lectures attendance should exceed 70% in order to attend the final unseen examination

Chemistry Chemistry deals with studying (properties) of matter and the

changes (behavior) that matter undergoes.

A property is any characteristic that allows us to recognize aparticular type of matter and to distinguish it from othertypes.

Matter is the physical material of the universe; it is anythingthat has mass and occupies space.

Properties of matter relate to both the kinds of atoms thematter contains (composition) and to the arrangements ofthese atoms (structure)these atoms (structure).

Chemists wish to understand: Is a certain material reactive for a change? Inorganic Why do reactions occur? Thermodynamics Which specific pathways they follow? Thermodynamics How fast they occur? Kinetics

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With thermodynamics chemists can Identify whether a certain reaction/process is possible (or

not) under a given set of conditions, e.g., temperature andpressure or concentration of reactants and products. (alsoidentify the pathway)identify the pathway)

Predict the effect of different variables on the extent of acertain reaction, which is important for selecting theoptimum conditions for maximum yield from a certainprocess.

Formulate relationships for maximum yields obtainablefrom a certain reaction. With these relations, we identifyhow far a particular reaction will proceed before reachingan equilibrium.

ThermodynamicsAlthough the principles of thermodynamics have beenin existence since the creation of the universe,thermodynamics did not emerge as a science until the

t ti f th fi t f l t h i tconstruction of the first successful atmospheric steamengines (were very slow and inefficient) in England byThomas Savery in 1697 and Thomas Newcomen in1712.

The first and second laws of thermodynamics emergedsimultaneously in the 1850s primarily out of the workssimultaneously in the 1850s, primarily out of the worksof William Rankine, Rudolph Clausius, and Lord Kelvin(formerly William Thomson).

The term thermodynamics was first used in apublication by Lord Kelvin in 1849.

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Power  GenerationThe concept of generating power have passed with certain 

important stages:

The early discovery of fire: which gave warmth ,(دفء)ة تغذ nourishmentفة (تغذية) and the ability to craft (حرفة) objects

out of stone (حجر) and metal.

Fire alone would not have allowed humans to survive

Tools manufacturing: knives ,(سكاكين) spearheads ( رأسة ل ل ,(الحربةل wheels ;(عجلات) levers (العتلات) and pulleys (البكرات)(can lift heavier loads than any elephant).

Tools improved slowly ;

Wheelbarrows ( اليد عربات ) evolved into horse drawn carts

Stones for grinding grain became windmills ( الھواء طواحين ).

Power  GenerationMachines driven by Animals, water and wind:

They were all insufficient (lack of power)• Winds are unreliable, • There are a finite number of sites with running water,There are a finite number of sites with running water, • Only a few horses can be hitched to a cart at one time.

Steam engine : (a little over 300 years ago) A device that operates continuously, producing motion

(work) as long as heat is supplied to it Gases expand when heated and exert tremendous

pressures that can be exploited to drive power plantspressures that can be exploited to drive power plants,aircraft and automobiles.

The only constraint on generating power is the amount ofheat available.

Heat is generated by burning fuel, capturing solarradiation, or splitting atoms in nuclear reactions.

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Important Questions

What is the relation between heat and work? 

How much work can be obtained if a given amount of fuel is burned? f f

Can the performance of engines be improved? 

Thermodynamics was the science that grew from efforts to answer these questions.

Thermodynamics“The study of energy and its transformations”

“The science of energy”

Energy can be viewed as the ability to cause changes

The name “Thermodynamics” stems from the Greek wordstherme (heat) and dynamis (power), which is mostdescriptive of the early efforts to convert heat into power.

Today the same name is broadly interpreted to include allaspects of energy and energy transformations includingpower generation, refrigeration, and relationships amongthe properties of matter.

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Thermodynamics vs. Thermochemistry Thermodynamics ‐ The study of the relationship

between heat, work, and other forms of energy.

Thermochemistry ‐ A branch of thermodynamics whichThermochemistry ‐ A branch of thermodynamics whichfocuses on the study of heat given off or absorbed in achemical reaction or studies the relationshipbetween heat and chemical reactions

Thermochemistry is a very important field of study because: It h l t d t i if ti l ti ill t It helps to determine if a particular reaction will occur or not If occurred, will it release or absorb energy ? It estimates how much energy a reaction will release orabsorb (determines if this Rx is economically feasible)

Thermochemistry, however, does not predict how fast areaction will occur.

Thermodynamics is a quantitative subject

It is concerned with macroscopic aspects of the interactionof matter with energy in its various forms.

It allows us to derive relations between the values ofnumerous physical quantities.

Some physical quantities, such as a mole fraction, aredimensionless; the value of one of these quantities is apure number.

Most quantities, however, are not dimensionless and theirvalues must include one or more units.

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Laws of ThermodynamicsEnergy can be viewed as the ability to cause changes

Thermodynamics is contained implicitly ( ً (ضمنيا within twoapparently simple statements called the First and Secondapparently simple statements called the First and SecondLaws of Thermodynamics

These two laws deals with energy‐the first, explicitly, andthe second, implicitly.

W h t d i ti k i tWe have no energy meters, no device we can stick into asystem which will record its energy.

Every form of energy is known only as a function of othervariables

First Law of Thermodynamic

During an interaction, energycan change from one form to

h b h l f

Principle of Energy Conservation

another but the total amount ofenergy remains constant.

Energy cannot be created ordestroyed.

i dEnergy is conserved

You don't get something for nothing

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Second Law of Thermodynamic

Even within the framework of

Energy has quality as well as quantity, and actual processes occur in the direction of decreasing quality of energy. 

A cup of hot coffee left energy conservation, you can nothave it just any way you mightlike it.

If you think things are going tobe perfect, forget it.

p f ff fon a table eventually cools, but a cup of cool coffee in the same room never gets hot by itself

Heat flows in the direction of decreasing T

The high‐T energy of the coffee isdegraded (transformed into a lessuseful form at a lower T) once it istransferred to the surrounding air.

Classical Thermodynamics (focus of this course)is a macroscopic approach (easy/direct) of studyingthermodynamics that do not require a knowledge of thebehavior of individual particles composing a substance.

E P( ) i t i i th lt f t t fE.g., P(gas) in a container is the result of momentum transferbetween the molecules and the walls of the container.However, one does not need to know the behavior of gasparticles to determine the P in the container. It would besufficient to attach a pressure gage to the container.

Statistical Thermodynamicsis a microscopic approach based on the average behavior oflarge groups of individual particles, is called statisticalthermodynamics.

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Applications of ThermodynamicsAll activities in nature involve some interaction between 

energy and matter

The heart is constantly pumpingbl d t ll t f th h

Human body

blood to all parts of the humanbody.

Various energy conversionsoccur in trillions of body cells.

The body heat generated is constantly rejected to theThe body heat generated is constantly rejected to theenvironment.

The human comfort is closely tied to the rate of thismetabolic heat rejection.

We try to control this heat transfer rate by adjusting ourclothing to the environmental conditions.

Applications of Thermodynamics

The energy‐efficient home is designedon the basis of minimizing heat loss inwinter and heat gain in summer.

solar hot water system

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Applications of ThermodynamicsMany ordinary household utensils أواني and appliances الأجھزة are designed, in whole or in part, by using the 

principles of thermodynamics

Electric or gas range,

Heating/air‐conditioning sys.,

Refrigerator,

Humidifier,

Pressure cooker,

Refrigerator

,

Water heater,

Shower,

Iron,

Computer and TV.

Applications of ThermodynamicsIt plays a major part in the design and analysis of

rigerator

Boats Cars

Refr

AircraftPower plants

Food processing

Piping network

Wind turbines

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Lecture 1 

Introduction and 

Basic ConceptsBasic Concepts

UNITS OF MEASUREMENT The United States has traditionally used the English system,

although use of the metric system has become more common

The volume printedon this soda can inboth English units(fluid ounces fl oz)(fluid ounces, fl oz)and metric units(milliliters, mL).

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SI Base UNITS In 1960 an international agreementwas reached specifying a particularchoice of metric units for use inscientific measurements.

These preferred units are called SIunits, after the French SystèmeInternational d’Unités.te at o a d U tés.

This system has seven base unitsfrom which all other units are derived

ExercisesWhich quantity is the smallest: 1 mg, 1 g, or 1 pg? 1 pg

What is the name of the unit that equals (a) 109 gram , (b)106 second (c) 103 meter? ng s mm10 6 second, (c) 10 3 meter? ng, s, mm.

Howmany picometers are there in one meter? 1012 pm

Express 6.0 ×103m using a prefix to replace the power often? 6.0 km.

Use exponential notation to express 4.22 mg in grams?4.22 ×103 g.

Use decimal notation to express 4.22 mg in grams? 0.00422 g

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Derived SI Units (Volume) Volume is not a

fundamental SI unitbut derived fromlength.

A cube that measuresA cube that measures1 meter (m) on eachedge has a volume of(1 m)3 =1 m3.

Because 1m = 10 dm,the volume of thiscube is (1 m)3 = (10dm)3 = 1000 dm3.

A cubic decimeter (1dm)3 is commonlycalled a liter (L)

1L = (1 dm)3 = (10cm)3 = 1000 cm3

Other Derived SI Units

DefinitionDerived Unit

Name of SI unit

Symbol (s)

Physical quantity

s1HzHertzν, fFrequency

2 1kg m s2  = J m1NNewtonFForce

N m= kg m2 s2JJouleE, H,V, etcEnergy

N m2 = kg m1s2PaPascalPPressure

J s1 = kg m2 s3WWattpPower

A sCCoulombQCharge

JA s1VVoltE,…etcPotential

V A1ΩOhmRResistance

Ω1SSiemensGConductance

C V1FFaradCCapacitance

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Other UnitsSI unitSymbolPhysical quantity

m2

m3

m s1

AV

U, V, c

AreaVolumeVelocity

m s2

Nkg m3

dm3

105 Nmol dm3

4.18 J

, ,a, gG,Wp

liter (l)dyne (dyn)Molar (M)Calorie (Cal)

yAcceleration

WeightDensityVolume Force

ConcentrationEnergy 4.18 J

107 J1.013 x 105 Pa133.322 Pa133.322 Pa105 Pa

760 mm Hg = 76 cm Hg

Calorie (Cal)Erg (erg)

Atmosphere (atm)(mm Hg)Torr (torr)

BarAtmosphere

EnergyEnergyPressurePressurePressurePressurePressure 

Mass vs. weightThe term weight is often incorrectly used to express mass.

Unlike mass, weight W is a force. It is the gravitationalforce applied to a body, and its magnitude is determinedf N t ’ d lfrom Newton’s second law,

where m is the mass of the body, and g is the localgravitational acceleration (g is 9.807 m/s2 at sea level and45° latitude)

)(NmgW

45 latitude).

The mass of a body remains the same regardless of itslocation in the universe. Its weight, however, changes witha change in gravitational acceleration. A body weighs lesson top of a mountain since g decreases with altitude.

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Work It is a form of energy and can simply be defined as force

times distance; therefore, (N∙m),” which is called a joule (J).That is,

NmJ 1The amount of energy needed to raise the temperature of 1 

g of water at 14.5°C by 1°C is defined as 1 calorie (cal), and 1 cal = 4.1868 J.

NmJ1

Feel the UnitIf you light a typical match and let itburn itself out, it yieldsapproximately one kJ of energy

Power It is the time rate of energy or the rate of doing work

Its unit is joule per second (J/s), which is called a watt (W)

Electrical energy typically is expressed in the unit kilowatt‐hour (kWh), which is equivalent to 3600 kJ.

An electric appliance with a rated power of 1 kW consumes1 kWh of electricity when running continuously for onehour

When dealing with electric power generation, the units kWand kWh are often confused.

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PowerNote that kW or kJ/s is a unit of power, whereas kWh is a

unit of energy.

Therefore, statements like “the new wind turbine willgenerate 50 kW of electricity per year” are meaninglessand incorrect.

A correct statement should be something like “the newwind turbine with a rated power of 50 kW will generatewind turbine with a rated power of 50 kW will generate438000 kWh of electricity per year.”

Dimensional Analysis  (unit factor method)

It is a method used to convert a given result from one system ofunits to another. Apples and oranges do not add

Consider a pin measuring 2 85 centimeters in length What is its Consider a pin measuring 2.85 centimeters in length. What is itslength in inches?

======================================================= From Tables, we know that 2.54 cm = 1 in If we divide both sides of this equation by 2.54 centimeters, we

getis called a unit factor

cm

in

542

11 Multiplying any expression by this unit factor will not change its

value.

The unit factor does not affect the significant figures

cm54.2

inincm

incm 12.154.2

.852

54.2

1 85.2

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Chemical oxygen demand (COD) 

In environmental chemistry, COD test is commonlyused to indirectly measure the amount of organiccompounds in water.

AnEMBR (1) Gr‐HFM bundle, (2)bioanode, (3) power source, (4)

Anaerobic electrochemical membrane bioreactors

( ) p ( )external resistor, (5) gas bag, (6)pressure sensor, (7) pump, and (8)permeate. Bubbles representdifferent gases: CO2 (light blue),H2 (green), and CH4 (yellow).

Environ. Sci. Technol. 2016, 50, 4439−4447

Energy from Wastewater

ExerciseWhat is potential energy benefit of maximum energy recovery

using domestic wastewater to a town of 100,000 people?

a) Calculate the maximum energy production for assuming500 L/d per capita 300 mg/L of COD and 14 7 kJ/g COD500 L/d per capita, 300 mg/L of COD, and 14.7 kJ/g COD(based on wastewater solids)?

b) How much is this electricity worth at $0.44/kW‐h?

c) How many homes would this power, assuming 1.5kW/home?

AnswerAnswerCalculate power in megawatts (MW)

MW

kW

MW

h

d

 kJ

kWh

g

kJ

mg

g

d

L

L

mgP

 6.2

 10 24

 1

3600

 1

COD 

 7.14

10cap10

cap 

 005COD 300

33

5

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b) The result above is for continuous power generation, soconverting it to kWh and using the given electricity cost, wecalculate the value of this power as (SI Unit of year (Julian) is“a”)

163

1010$1

 3652410.440 $ 6.2

yr

h

MW

kW

kWhMWValue

Thus, power could be worth as much as $10 million per year.

c) The number of homes ( h ) served with this power is just the ratioof the power generated to electricity needed per home, or

1

yyrMWkWh

eskWes

MWh hom170010hom

623

Hint: These calculations all assume 100% energy recovery, which isnot reasonable. As a goal, it is hoped to recover 25‐50% of theenergy and thus the above numbers should be reduced by one halfor more to obtain more practical results.

esMWkW

MWh hom1700 5.1

 6.2

Exercise A school is paying $0.12/kWh for electric power. To reduce its

power bill, the school installs a wind turbine with a rated powerof 30 kW. If the turbine operates 2200 hours per year at therated power, determine the amount of electric power generatedp , f p gby the wind turbine and the money saved by the school per year.

AnswerCalculate the total amount of electric energy generated per year

ervaltimetimeunitperEnergyEnergyTotal )int( kWhhkW

ervaltimetimeunitperEnergyEnergyTotal

 000,66) 2200(  30                         

)int( 

$7920 )($0.12/kWh ) 000,66(                          

) ost ( nergy otalavedoney 

kWh

of EnergycUnitETSM

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Alternatively

The annual electric energy production also could bedetermined in kJ by unit manipulations as

kJ

kW

skJ

h

shkWEnergyTotal

1038.2                         

 1

/ 1 

 1

 3600 ) 2200(  30 

8

which is equivalent to 66,000 kWh (1 kWh = 3600 kJ).

Temperature Temperature, a measure of the hotness or coldness of an object,

is a physical property that determines the direction of heat flow.

Heat always flows spontaneously from a substance at highertemperature to one at lower temperaturetemperature to one at lower temperature.

We feel the influx of heat when we touch a hot object.

The temperature scales commonly employed in science are theCelsius and Kelvin scales.

The Celsius scale was originally based on the assignment of 0 °Cto the freezing point of water and 100 °C to its boiling point atsea level

The Kelvin scale is the SI temperature scale, and the SI unit oftemperature is the kelvin (K).

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TemperatureZero on the Kelvin scale is the lowest attainabletemperature, 273.15 °C, referred to as absolutezero

The Celsius and Kelvin scales have equal‐sizedunits.

K = °C + 273.15

The common temperature scale in the UnitedThe common temperature scale in the UnitedStates is the Fahrenheit scale.

Water freezes at 32 °F and boils at 212 °F.

rison

)32(59 CF

K = °C + 273.15

les compar

Sca

)32(95 FC

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ExercisesNormal body temperature is 98.6°F. Convert this temperature tothe Celsius and Kelvin scales?

======================================================= The number of Fahrenheit degrees between 32.0°F and 98.6°F isf g

66.6°F. We must convert this difference to Celsius degrees:

Thus 98.6°F corresponds to 37.0°C. Now we can convert to the

 Co37.032.0)(98.695Cο

Kelvin scale:

Note that the final answer has only one decimal place (37.0 islimiting)

ExercisesOne interesting feature of the Celsius and Fahrenheit scales isthat 40°C and 40°F represent the same temperature, asshown in Fig. R.5. Verify that this is true?

=======================================================

• The difference between 32°F and 40°F is 72°F. The differencebetween 0°C and 40°C is 40°C. The ratio of these is

CoFo

CoFo

CoFo

59

5898

4072

as required. Thus 40°C is equivalent to 40°F.

CCC 55840

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SystemsA system: a quantity of matter or a region in space chosenfor study or volume of interest (e.g., reaction vessel, test tube)Surroundings: the mass or region outside the system.The boundary: the real or imaginary surface that separatesThe boundary: the real or imaginary surface that separatesthe system from its surroundings.

is the contact surface shared by both thesystem and the surroundings

The boundary of a system

can be fixed or movable.

Mathematically speaking, the boundaryhas zero thickness, and thus it canneither contain any mass nor occupy anyvolume in space.

Definitions

• Open system: matter can passbetween system & surroundings

• Closed system: matter cannot pass

surroundings

system

Open System

Energy

Matter

between system & surroundings

• Isolated system: Neither matternor energy can pass betweensystem & surroundings

• Diathermic Walls: Walls that doit t f h t

Open System

surroundingsystem

Closed System

Energy

permit energy transfer as heat(such as steel and glass) ('dia' isthe Greek word for "through").

• Adiabatic Walls: Walls that do notpermit energy transfer as heat.

surroundingssystem

Isolated System

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• Energy is the capacity of a system to do work

Hint: Heat flows by virtue of a temperature difference. Heatwill flow until temperature gradients disappear.

• Work is the transfer of energy by interaction between thesystem and the surroundings.system and the surroundings.

Mechanical work: the movement of an object through adistance

W = F . d = m . g . h (J)

(force) . (distance) = (mass).(acceleration) .(height)

=        P     .        A       .        h          =    P    .      V

(pressure) . (area ).(height) (pressure) . (volume)

Homogeneous (continuous) systems

The system has the same properties throughout itsextension (a single phase)

Heterogeneous (discontinuous) systems

The system is composed of a number of homogeneous parts(called phases)

A phase

Is a homogeneous, physically distinct, and mechanicallyseparable portion of any heterogeneous system.

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General conventions

The system can do work on the surroundings. Thesurroundings can also do work on the system.

If the system does work on the surroundings, then work (W) is negative.

If the surroundings does work on the system, then work (W) is positive.

If the system loses  heat to the surroundings, then work (q) is negative.

If the system gains  heat from the surroundings, then work (q) is positive.

State property (Functions): Functions which depend on the initialand final states of the system, not on the path it takes. (e.g.,Internal energy, Temperature, Volume, Pressure).

Path or non‐State property (Functions): Functions which dependnot only on the initial and final states of the system but also onnot only on the initial and final states of the system, but also onthe path it takes. (e.g., Heat and Work; written as dq or dW.Never written as Δq or ΔW).

Extensive property (Functions): Functions which depend on themass of the material (e.g., Internal energy, Volume )

Intensive Property (Functions): Functions which are independentof the mass of the material (e.g., Pressure, Temperature, Density,Molar quantities )Thermodynamics is largely concerned with the relations between 

state functions which characterize systems.

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Closed SystemsA closed system (also known as acontrol mass or just system whenthe context makes it clear) consistsof a fixed amount of mass and noof a fixed amount of mass, and nomass can cross its boundary. Thatis, no mass can enter or leave aclosed system.

Energy, in the form of heat or work, cancross the boundary of a closed system

System:  Gas

dy f y

The volume of a closed system does nothave to be fixed.

If, as a special case, energy is notallowed to cross the boundary, thatsystem is called an isolated system.

Boundary: inner surfaces of the piston and the 

cylinder

A Closed System with a moving boundary

Volume is changed

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Open SystemsAn open system, or a control volume, is a properly selected region in space. 

It usually encloses a device that involves mass flow such ast h t di t t bia water heater, a car radiator, compressor, turbine, or

nozzle.

Both mass and energy can cross the boundary.

A proper choice of an open system: consider the flow of airthrough a nozzle, a good choice for the control volumewould be the region within the nozzle.would be the region within the nozzle.

The boundaries of a control volume are called a control surface,and they can be real or imaginary.

In the case of a nozzle, the inner surface of the nozzle forms thereal part of the boundary, and the entrance and exit areas formthe imaginary part, since there are no physical surfaces there.

Open Systems

A control volume (CV) ith l d i i

A control volume (CV) with with real and imaginary 

boundariesfixed and moving boundaries as 

well as real and imaginary boundaries

A control volume can also involve heat and work, in addition to mass interaction.

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Example: a water heaterHow much heat must we transfer to thewater in the tank in order to supply asteady stream of hot water?

Since hot water will leave the tank and bereplaced by cold water, it is not convenientto choose a fixed mass as our system forthe analysis.

Instead, we can concentrate our attentionon the volume formed by the interiorsurfaces of the tank and consider the hotsurfaces of the tank and consider the hotand cold water streams as mass leavingand entering the control volume.

The interior surfaces of the tank form the control surface for this case, and mass is crossing the control surface at two locations.

StateA state : is a condition describing a system maintained atequilibrium when all properties (Variables) (measured orcalculated) throughout the entire system are fixed(unchanged)(unchanged)

If the value of even one property changes, the state willchange to a different one.

State 1State 2

State variables:

External: macroscopicvelocities or position State 2velocities, or positioncoordinates in an externalfield

Internal: P, V, m, etc of allsubstances in the system.

Intensive/extensive

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Intensive/extensive properties of a systemAny characteristic of a system is called a property.

Examples are pressure P, temperature T, volume V, andmass m, viscosity, thermal conductivity, modulus ofelasticity, thermal expansion coefficient, electric resistivity,and even velocity and elevation.

Intensive properties are those that are independent of themass of a system, e.g., temperature, pressure, and density.

Extensive properties are those whose values depend on thesize—or extent (mass)—of the system, e.g., Total mass,total volume, and total momentum.

Extensive properties per unit mass are called specificproperties. E.g., specific volume (v = V/m) and specific totalenergy (e = E/m).

EquilibriumThermodynamics deals with equilibrium states.

The word equilibrium implies a state of balance.

In an equilibrium state there are no unbalanced potentials(or driving forces) within the system.

A system in equilibrium experiencesNo change in all of its intensive properties with time

There are many types of equilibrium (thermal, mechanical,phase, chemical), and a system is not in thermodynamicequilibrium unless the conditions of all the relevant typesof equilibrium are satisfied.

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EquilibriumThermal equilibrium indicates keeping the temperature thesame throughout the entire system. That is, the systeminvolves no temperature differential, which is the drivingforce for heat flowforce for heat flow.

Mechanical equilibrium indicates no change in pressure atany point of the system with time.

Phase equilibrium (If a system involves two phases),indicates that the mass of each phase reaches anindicates that the mass of each phase reaches anequilibrium level and stays there.

Chemical equilibrium indicates no change in the chemicalcomposition of the system with time, that is, no chemicalreactions occur.

The State PostulateIs it required to specify all the properties in order to fix a state? 

The state postulate: The state of a simple compressible system iscompletely specified by two independent, intensive properties.

Once these two properties are specified, the rest of theproperties assume certain values automatically.

“simple compressible” refers to the absence of electrical,magnetic, gravitational, motion, and surface tension effects.

“independent”: as temperature and specific volume which areindependent : as temperature and specific volume, which arealways independent, and together they can fix the state of asimple compressible system.

Temperature and pressure, however, are independent propertiesfor single‐phase systems, but are dependent properties formultiphase systems

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ProcessesAny change that a system undergoes from one equilibriumstate to another is called a process.

The series of states through which a system passes during all d h h f hprocess is called the path of the process.

To describe a process completely, one should specify theinitial and final states of the process, as well as the path itfollows, and the interactions with the surroundings.

An isothermal process is a process during which thet t T i t ttemperature T remains constant.

An isobaric process is a process during which the pressure Premains constant.

An isochoric (or isometric) process is a process during whichthe specific volume v remains constant.

CyclesA system is said to have undergone a cycle if it returns to itsinitial state at the end of the process. That is, for a cycle theinitial and final states are identical.

“Steady” implies no change with time. The opposite ofsteady is unsteady, or transient.

0dU

“Uniform” implies no change with location over a specifiedregion.

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Quasistatic processesIf a process is running (e.g., the expansion of a gas) and thesystem is subjected to external influence (e.g., pressure)encountering (exactly) the force driving the expansion sothat the system is passing by a series of equilibrium statesthat the system is passing by a series of equilibrium states,this process is called “quasistatic process”.

These processes are imaginary and considered limiting fornatural process.

Other forces as friction may act against this idealization.

Reversible/irreversible processes

A reversible process:

Once a cup of hot coffee cools, it will not heat up by retrieving the heat it lost from the surroundings; Irreversible process

a process that can be reversed withoutleaving any trace on the surroundings.

both the system and the surroundings arereturned to their initial states at the end ofthe reverse process.

This is possible only if the net heat and net

Frictionless pendulum/ A reversibleThis is possible only if the net heat and net

work exchange between the system and thesurroundings is zero for the combined(original and reverse) process.

Processes that are not reversible are calledirreversible processes.

A reversible process

A system passes through a series of 

equilibriumstates during a 

reversible process.

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Temperature and heat transferTemperature is a property measuring the degree of“hotness” or “coldness” of a substance.

A cup of hot coffee left on the table eventually cools offand a cold drink eventually warms up (attaining a thermalequilibrium is driving).

Two bodies reaching thermalequilibrium after being brought into

contact in an isolated enclosure

Zeroth law of thermodynamics R H Fowler / 1931

If two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other

By replacing the third body with a thermometer, the zerothlaw can be restated as:

Two bodies are in thermal equilibrium if both have the same temperature reading even if they are not in contact.

The zeroth law was recognized more than half a centuryafter the formulation of the first and the second laws ofthermodynamics.“Zeroth” since it should have preceded the first and thesecond laws of thermodynamics.

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Pressure: a normal force exerted by a fluid per unit area

It has the unit (N/m2), which is called a pascal (Pa).

1 bar = 105 Pa = 0.1 MPa = 100 kPa

1 atm = 101,325 Pa = 101.325 kPa = 1.01325 bars

kilogram‐force per square centimeter1 kgf/cm2 = 9.807 N/cm2 = 9.807 × 104 N/m2 = 9.807 × 104 Pa

= 0.9807 bar= 0 9679 atm= 0.9679 atm

In the English system, the pressure unit is pound‐force per

square inch (lbf/in2, or psi), and 1 atm = 14.696 psi. Pressure is also used on solid surfaces as synonymous to

normal stress, which is the force acting perpendicular to thesurface per unit area.

A 150‐pound person with a total foot imprint area of 50 in2

exerts a pressure of 150 lbf/50 in2 = 3.0 psi on the floor.

If the person stands on one foot, the pressure doubles.

If the person gains excessiveIf the person gains excessiveweight, he or she is likely toencounter foot discomfortbecause of the increasedpressure on the foot (the size ofthe bottom of the foot does notchange with weight gain)

This explains: how a person can walk on fresh snow without sinking by wearing

large snowshoes. how a person cuts with little effort when using a sharp knife.

change with weight gain).

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Variation of P with depthPressure in a fluid increases with depth because more fluidrests on deeper layers, and the effect of this “extra weight”on a deeper layer is balanced by an increase in pressure.

zP

zgPP

sabove

abovebelow

          

s fluidtheof  weight specific

Volume

(force) weight     

A diver experiences a high pressure when diving deeper in a 

lake

Variation of P with depthFor small to moderate distances, the variation of pressurewith height is negligible for gases because of their lowdensity (weight).

For fluids whose densitychanges significantly withelevation

gdz

dP

Pressure in a fluid (not solid surfaces) at rest is independentf th h ti f th t i It hof the shape or cross section of the container. It changes

with the vertical distance, but remains constant in otherdirections.

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Pascal’s law (1623–1662)

21 PP

The force applied by a fluid is proportional to the surface area

11

2

2

1

1

21

AFA

F

A

F

22 AF

If two hydraulic cylinders of different areas are connected,the larger exerts a proportionally greater force than thatapplied to the smaller.

Exercise Determine the atmospheric pressure at a location where the

barometric reading is 740 mmHg and the gravitationalacceleration is g = 9.805 m/s2. Assume the temperature ofmercury to be 10°C, at which its density is 13,570 kg/m3.y , y , g/

Solution

ghPatm kPaN 1123

kPa .  

 N/m

kPa

 kg∙m/s

Nm) .)(m/s.)(kg/m,(

 598         

1000

1

1

17400805957013 

22

23