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Course: Stoichiometry11/21/2010

Department of Polymer & Process Engineering, U.E.T. Lahore

Industrial Stoichiometry

G.M.Mamoor

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DefinitionThe word Stoichiometry comes from the Greek stoicheion, whichmeans to measure the elements A good definition of the terms meaning in the study of

chemistry is the quantitative study of reactants and productsin a chemical reaction

Stoichiometry allows one to calculate how much of a givenproduct a reaction is expected to produce based on how much ofthe reactants are available

Given the mass, volume and density, or the number of moles ofreactants, one can calculate the mass, volume (if the density isknown) or moles of product

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Why do we care about stoichiometry?

a. This is real chemistry! That is, you will be able to predict how

much of some chemical will be produced based on the starting

amounts of the reactants. Also, you will be able to calculate howmany grams of reactants will be needed to produce a given amount

of some other chemical.

b. Example: If I know how much steel I need, then how many tons

of iron and carbon will be needed to produce that quantity of steel?

c. Example: If I know how many tons of flour, eggs, milk, and

sugar that I have, then how many cakes could I produce using a

given recipe?

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Molar Ratios

Calculations using stoichiometry depend on the molarrelationships in chemical equations; this is why a properly

balanced chemical equation is so importantA properly balanced chemical equation shows the molarratios of each of the species present, whether they arereactants or products

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Take the combustion of propane as an example:

C3H8 + 5O2 --> 3CO2 + 4H2O

The ratios found in this equation are as follows:1 mol propane:5 mol oxygen

(each mole ofC3H8 requires five moles of O2 to burn completely)

1 mol propane: 3 mol carbon dioxide(each mole of completely burned C3H8 produces three moles ofCO2)

1 mol propane: 4 mol water(each mole of completely burned C3H8 produces four moles ofH2O)

5 mol oxygen: 3 mol carbon dioxide

(for every five moles of O2 consumed, three moles ofCO2 are produced)

5 mol oxygen: 4 mol water(for every five moles of O2 consumed, four moles ofH2O are produced)

3 mol carbon dioxide:4 mol water(for every three moles ofCO2 produced, 4 moles ofH2O are produced)

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A review of how chemical reactions occur and the meaning of a chemical equation

a. What is happening to atoms and molecules during a chemical reaction?

1. . Consider the unbalanced chemical equation for the reaction of hydrogen and

oxygen below:

ii. Now, consider the actual molecules reacting with each other:

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What is the meaning of the coefficients in a chemical equation?

i. The coefficients in the equation, therefore, tell us how many molecules or moles of

each substance are needed for the reaction to occur.

ii. It is important to remember that these coefficients do NOT tell us the ratio of grams

of each substance. Just because there are two moles of H2 needed to react with each mole

of O2 does NOT mean that there are two GRAMS of hydrogen needed for every GRAM of

oxygen. That would only be the case of each mole of O2 weighed as much as each mole of

H2, and the periodic table shows that this is clearly not the case.

iii. Thus, in order to use a chemical equation to predict the amounts of substances usedin chemical reaction, we must always solve such a problem using moles as our unit of

matter. Additional conversion steps will be required if the problem does not actually

supply or ask for the number of moles.

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#Course: SHMT11/21/20107

Topics to be covered today

What does polymer and process engineer do for aliving

Units and dimensions

SI units American engineering system units

SI prefixes

Conversion of units

Gravitational conversion factor Numerical problems.

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WHAT DOES ACHEMIST DO ?

WHAT DOES ACHEMICAL ENGINEER DO ?

WHAT DOES A POLYMER ENGINEER DO ?

WHAT DOES A PROCESS ENGINEER DO ?


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It i tr t at pr ngin r ar comfortable with

chemistry, b t t d r wit t i kn wl dg

t an j t ak i al . In fa t, t term process

engineer" i n t v n int nd d t d rib t t p f

w rk a pr ngin r p rf r . In t ad it is meant

to reveal what makes the field different fr t other

branches of engineering.

All engineers employ mathematics, physics, and the

engineering art to overcome technical problems in a

safe and economical fashion.


Process Engineer

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Yet, it i t e pr ess engineer al ne t at draws up n t e

vast and p werful science of chemistr to solve a wide

range of problems. The strong technical and social tiesthat bind chemistr an pr ocess engineering are unique in

the fields of science and technolog . This marriage

between chemists and pr ocess engineers has been

be

nefi

cial t

ob

oth s

ides

andha

srig

htf

ull br

oug

ht t

he

env of the otherengineering fields.


Process Engineer

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Universal engineer

The breadth of scientific and technical knowledgeinherent in the profession has caused some todescribe the process engineer as the "universalengineer. Despite a title that suggests aprofession composed of narrow specialists, processengineers are actually extremely versatile and ableto handle a wide range of technical problems.


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So What Exactly Does This "Universal Engineer" Do?

During the past Century, process engineers havemade tremendous contributions to our standard of

living. To celebrate these accomplishments, theAmerican Institute of Chemical Engineers (AIChE)has compiled a list of the "10 GreatestAchievements of process Engineering." Thesetriumphs are summarized Next:


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The Atom, as Large as Life

The Plastic Age

The Human Reactor

Wonder Drugs for the Masses

Synthetic Fibers, a Sheep's Best Friend

Process Engineer

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Liquefied Air, Yes it's Cool

The Environment, We All Have to Live Here

Food, "It's What's For Dinner

Petrochemicals, "Black Gold, Texas Tea

Running on Synthetic Rubber


Process Engineer

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Process Engineering Today & Tomorrow

The "Big five" engineering fields consist ofcivil, mechanical,electrical, chemical and Process engineers. Of these,chemical/process engineers are numerically the smallestgroup. However, this relatively small group holds a veryprominent position in many industries, and process

engineers are, on average, the highest paid of the "Big five" (WAGES).

More typically, process engineers concern themselves withthe chemical processes that turn raw materials into valuableproducts. The necessary skills encompass all aspects of

design, testing, scale-up, operation, control, andoptimization, and require a detailed understanding of thevarious "unit operations", such as distillation, mixing, andbiological processes, which make these conversions possible.


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Today there are around 25,000 practicingchemical engineers and about 7,000process engineers in Pakistan .polymerand process engineering is not a professionthat has to dwell on the achievements of thepast for comfort, for its greatestaccomplishments are yet to come.


Process Engineer

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Introduction : UNITS

Describe the basic techniques for thehandling of units and dimensions incalculations.

Describe the basic techniques forexpressing the values of process variablesand for setting up and solving equationsthat relate these variables.

Develop an ability to analyze and workengineering problems by practice.


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Units and Dimensions

Convert one set of units in a function orequation into another equivalent set for mass,length, area, volume, time, energy and force

Specify the basic and derived units in the SI andAmerican engineering system for mass, length,volume, density, time, and their equivalence.

Explain the difference between weight and

mass Apply the concepts of dimensional consistency

to determine the units of any term in a function


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Units andD

imensions Dimensions: are properties that can be measured such as

length, time, mass, temperature, or calculated by multiplyingor dividing other dimensions, such as velocity (length/time)

Units: are means of expressing the dimensions such as feetor meter for length, hours/seconds for time.

Measured units are specific values of dimensions defined bylaw or custom. Many different units can be used for a singledimension, as inches, miles, centimeters are all units used tomeasure the dimension length.

Every valid equation must be dimensionally homogeneous:that is, all additive terms on both sides of the equation musthave the same unit

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Units and Dimensions

Consider

1. 110 mg of sodium

2. 24 hands high

3. 5 gal of gasolineWe'll break them up this way


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Types ofDimensions

Fundamental dimensions

Derived dimensions

The "fundamental dimensions" (length, time, mass,

temperature, amount) are distinct and are sufficientto define all the others. We also use many deriveddimensions (velocity, volume, density, etc.) forconvenience.


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Dimensions

Dimension Symbol

Length

Mass

time

force

electric current

absolute temperature

luminous intensity

[L]

[M]

[T]

[F]

[A]

[UA

?/]

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Units and Calculations

It is always good practice to attach unitsto all numbers in an engineeringcalculation. Doing so

1. attaches physical meaning to the numbersused,

2. gives clues to methods for how theproblem should be solved, and

3. reduces the possibility of accidentallyinverting part of the calculation


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Addition and Subtraction

Values MAY be added if UNITS are the same.

Values CANNOT be added ifDIMENSIONSare different.

Examples:1:

different dimensions: length, temperature --so cannot be added.

2:

same dimension: length, different units -- can add


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Multiplication and Division

Values may be combined; units combine insimilar fashion.

Examples:

You cannot cancel or lump units unless theyare identical.


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Functions

Trigonometric functions can only haveangular units (radians, degrees). All otherfunctions and function arguments, including

exponentiation, powers, etc., must bedimensionless.

Examples:

Is OK but

is meaningless


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CONVERSION OF UNITS

A measured quantity can be expressed interms of any units having the

appropriate dimension To convert a quantity expressed in terms

of one unit to equivalent in terms ofanother unit, multiply the given quantity

by the conversion factor


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CONVERSION OF UNITS

EXAMPLE: Convert 5 m.p.h. to yds/week

EXAMPLE: What is the conversion factor between Btu/h and W?


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Systems of Units

Most engineering problems use one of two systemsof units

SI (Systeme Internationale): is commonly used byscientists. It is in everyday use in most of the

world. The so-called "metric system" is asubset/variant of the SI system, which was officiallystandardized in 1960.

Engineering (American, English, fps): is thetraditional system of the US and UK. Although the

UK changed official systems in the 1970s, the UShas not. The vast majority of US industrial concernsstill specify parts and equipment using these"Engineering" units.


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SYSTEMS OF UNITS

Components of a system of units:

Base units - units for the dimensions of mass,length, time, temperature, electrical current, andlight intensity.

Derived units - units that are obtained in oneor two ways;

By multiplying and dividing base units also referred to

as compoundunits

Example: ft/min (velocity), cm2(area), kg.m/s2 (force)

SI and American engineering system units.


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Common Systems of Units

B a s e U n i ts

Q u a n t i ty S I s y m b o l A m e r ic a n E n g . s y m b o l

L e n g t h M e t er m F o o t f t

M a s s K i l o g r am k g P o u n d m a s s Ib m

M o l e s G r a m - m o l e m o l e P o u n d m o l e Ib m o l e

T im e S ec o n d s S e c o n d ,h o u r s ,h r

T e m p e r a t u r e K e l v i n 0K / K R a n k i n e 0R /R


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33

SI UnitsDimension SI Unit Definition

Length meters (m) Distance traveled by light

in 1/(299,792,458) s

Mass kilogram (kg) Mass of a specificplatinum-iridium hallow

cylinder kept by Intl.

Bureau of Weights and

Measures at Svres, France

Time seconds (s) 9,192,631,700 oscillations

of cesium atom


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SI Units

Standard Kilogramat Svres


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SI Prefixes

nano

micro

milli

centi

deci

deka

hecto

kilo

mega

giga

PrefixDecimal Multiplier

Symbol

10-9

10-6

10-3

10-2

10-1

10+1

10+2

10+3

10+6

10+9

n

Q

m

c

d

da

h

k

M

G

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FORCE, WEIGHT AND MASS

Force is proportional to product of mass and accelerationand is defined using derived units to equal the naturalunits;

1 Newton (N) = 1 kg.m/s2

1 dyne = 1 g.cm/s2

1 Ibf = 32.174 Ibm.ft/s2

Weight of an object is force exerted on the object bygravitational attraction of the earth i.e. force of gravity, g.

To convert a force from a derived force unit to a naturalunit, a conversion factor, gc must be used.

A ratio of gravitational acceleration, g to gc may be usedfor most conversions between mass and weight.

cg

maF !

2f

mc

seclb

ftlb32.174g !


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FORCE, WEIGHT AND MASS

1. F = m a /g c : W = m g /g c

k g . m / s 2 g . c m / s 2 I bm. f t / s 2

2 . gc = 1 --------- = 1 --------- = 32 .174 -----------N d y n e Ib f

3 . g = 9 .8066 m /s 2 ===> g /g c = 9 .8066 N /kg

g = 980 .66 cm /s 2 ===> g /g c = 980 .66 d yn e /g

g = 32.174 f t /s 2 ===> g /g c = 1 Ib f / Ib m

4 . E x a m p l e : W a t er h a s a d e n s i t y o f 6 2 .4 Ib m/ft3 . How

m u c h d o e s 2 .0 00 f t 3 o f w a te r w e i g h ?


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Example

The density of a fluid is given by the empiricalequation

V = 1.13 exp(1.2 x 10-10 P)

Where V = density in g/cm3

P = pressure in N/m2

a) What are the units of 1.13 and 1.2 x 10-10?

b) Derive the formula for V(Ibm/ft3) as a function of P(Ibf/in2)

A column of mercury is 3 mm in diameter x 72 cmhigh. If the density of mercury is 13.6 g/cm3, what isits weight in N. What is its weight in Ibf? What is itsmass in Ibm?


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Example The Reynolds number is the dimensionless quantity

that occurs frequently in the analysis of the flow offluids. For flow in pipes it is defined as DVV/Q,where D is the pipe diameter, V is the fluid velocity,V is the fluid density, and Q is the fluid viscosity.For a particular system having D = 4.0 cm, V = 10.0ft/s, V = 0.700 g/cm3, and Q = 0.18 centipoise (cP)(where 1 cP = 6.72 x 10-4 Ibm/ft.s). Calculate the

Reynolds number.


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Course: Stoichiometry11/21/2010 Department of Polymer & Process Engineering, U.E.T. Lahore

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Course: Stoichiometry11/21/201 Department of Polymer & Process Engineering U E T Lahore

Documents

Intro 4Nov