Neraca Massa Dan Energi

MASS AND ENERGY BALANCES

Wa Ode Cakra Nirwana, ST., MT.

Chemical Engineering DepartmentEngineering Faculty

University of Brawijaya

Presented by

Introduction

Aspek penilaian Unsur penilaian PresentasePemahaman Tugas 20 %

Quiz 1 dan 2 @ 20 %Ujian Akhir Semester (UAS) 30 %

Softskill Kreativitas dalam diskusi, kedisiplinan pengumpulan tugas, partisipasi di kelas, dsb

Tata Cara Penilaian

Chemical Engineering Calculations

Unit & Dimension

Dimensions: our basic concepts of

measurements such as length, time, mass,

temperature and so on

DEFINITION

Unit: expressing the dimensions, such as feet or centimeters for length, or hours or seconds for time

You can add, substract or equate numerical quantities only if the units of thequantities are the same

5 kg + 2 J

Example

Can not carrried out because the units of the two tems aredifferent

10 lb + 5 gr Can be performed (because the dimensions are the same, mass)Only after the units are transformed to be the same, either lb, gr and so on

Example:

Add the following:a) 1 ft + 3 sb) 1 hp + 300 W

Solution:

Add the following:a) 1 ft has the dimensions of length whereas 3 s has the dimensions of time, so it

has no meaning since the dimensions of the two terms are not the same

b) 1 hp + 300 W The dimensions are the same (energy per unit time) but the units are different.The two quantities must be transformed into like units, such as hp or watts before the addition can be carried out.1 hp = 746 watts 1 hp + 300 W = 746 W + 300 W = 1046 W

Physical Quantity

Name of Unit Symbol for Unit

Definition of Unit

BASIC SI UNITS

Length meter m

Mass kilogram kg

Time second s

Temperature Kelvin K

Amount of substance

mole mol

DERIVED SI UNIT

Energy joule J kg.m2.s-2

Force newton N kg.m.s-2 or J. m-1

Pressure Newton per square meter, pascal

N.m-2, Pa

Heat capacity Joule per (kilogram.kelvin)

J.kg-1.K-1

Physical Quantity

Name of Unit Symbol for Unit

BASIC AMERICAN SYSTEM UNITS

Length feet ft

Mass pound lbm

Force pound lbf

Temperature Degree Rankine 0R

Time Second, hour s, hr

DERIVED AMERICAN SYSTEM UNIT

Energy Foot pound (force) Btu, (ft)(lbf)

Power horsepower hp

Pressure Pound (force) per square inch Lbf/in2

Heat capacity Btu per pound (mass) per degree F

Btu/(lbm.0F)

Conversion of Units and Conversion Factors

Conversions factors are statements of equivalent values of different units in the same system or between systems of

The concept is to multiply any number and its associated units with dimensionless ratios termed

conversion factors to arrive at the desired answer and its associated units

Example:

Solution:

If a plane travels at twice the speed of sound (assume that the speed of sound is 1100 ft/s), how fast is it going in miles per hour?

Conversion of SI units is simpler than conversions in the American Engineering system

Example: We use Newton’s Law to compare the respective units:F = Cma

F = ForceC = a constant whose numerical value and units depend on those selected for F, m and am = massa = acceleration

SI Unit:

American Engineering System:

In the SI system, unit of force is newton (N) if C = 1 N/(kg)(m)/s2 then when 1 kg is accelerated at 1 m/s2

In the American Engineering system, unit of force is pound (force), (lbf) if C then when the inverse of the conversion factor with the

Numerical value 32.174 included is given the secial symbol gc

Note:The pound (mass) and pound (force) are not the same units in the American Engineering system

Example:

Solution:

One hundred pounds of water is flowing through a pipe at the rate of 10.0 ft/s. What is the kinetic energy of this water in (ft)(lbf)

Kinetic energy = K = ½ mv2

Assume that the 100 lb of water means the mass of the water

Dimensional ConsistencyA basic principle exists that equations must be dimensionally consistent

The principle: Each term in an equation must have the same net dimensions and units as every other term to which it is

added or substracted or equated

Dimensional considerations can be used to help identity the dimensions and units

of terms or quantities in an equationExample:

The microchip etching roughly follows the relation:d is the depth of the etch in µm and t is the time of the etch in seconds. What are the units associated with the number 16.2 and 0.021? Convert the relation sothat d becomes expressed in inches and t in minutes! Solution:

Both values of 16.2 must have the units of microns. The exponential must be dimensionless So that 0.021 must have the units of 1/s

The mole Unita mole is a certain number of molecules, atoms, electrons or other specified types of particles.

In the SI a mole is composed of 6.02 x 1023 molecules g mol is equal to mole

The g mol = mass in g molecular weight

The lb mol = mass in lb molecular weight

Mass in g = (mol. wt)(g mol)

Mass in lb = (mol. wt)(lb mol)

Example:

Solution:

If a bucket holds 2.00 lb of NaOH (mol.wt. = 40.0), how many(a) Pound moles of NaOH does it contain(b) Gram moles of NaOH does it contain

Conventions In Methods of Analysis and Measurement

DensityDensity is the ratio of mass per unit volume (kg/m3 or lb/ft3)Density for liquids and solids do not change significantly at ordinary conditions with pressure but they do change with temperature

Specific GravitySpecific gravity is a dimensionless ratio that can be considered as the ratio of two

Densities – that of the substance of interest, A, to that of a reference substance

The reference substance for liquids and solids is normally waterThe specific gravity of gases frequently is reffered to air or maybe referred to other gases

Example:

Solution:

Specific VolumeThe spesific volume of any compound is the inverse of the density, that is, the

volume per unit mass or unit amount of material. Units of specific volume might be ft3/lbm, cm3/g, m3/kg.

Mole Fraction and Mass (Weight) Fraction

Example:

Solution:

Analyses

Example:

Solution:

Concentration

Example:

Solution:

The current OSHA 8 hours limit for HCN in air is 10 ppm. A lethal dose of HCN in air(from the Merck Index) is 300 mg/kg of air at room temperature. How many mg HCN/kg air is the 10 ppm? What fraction of the lethal dose is 10 ppm?

Basis: 1 kgmol of the air/HCN mixture

The 10 ppm is because the amount of

HCN is so small. Then

Example:

Solution:

NOTESIt is important to remember that in an ideal solution, such as in gases or in

a simple mixture of hydrocarbon liquids or compounds of like chemical nature, the volumes of the components maybe added without great error to get the total volume of the mixtureFor the so-called nonideal mixtures this rule does not hold and the total volume

of the mixture is bigger or smaller than the sum of the volumes of the pure components

Example:

Solution:

Example:

Solution:

Temperature

Temperature Scales

Example:

Solution:

Pressure

Example:

Solution:

Example:

Solution:

Example:

Solution:

The Chemical Equation and Stoichiometry

Example:

Solution:

Example

If more than one product and more than one reactant are involved, the reactant upon which the yield is to be based must be clearly stated. Supposethat we have a reaction sequence as follows:

Example:

Solution:

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