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Lecture#3
Chemical Process Calculations
( PEVA ZC321/PEAB ZC 321)
By
Samir R. Kale, Chemical Engg Faculty, BITS, Pilani
BITS Pilani samirr@pilani.bits-pilani.ac.in
Mobile No- 09030279063
Pilani|Dubai|Goa|Hyderabad
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Topic Covered so far :

Unit Conversions: Volume, Pressure, Power, Mass, Length and Time

How to do ?

Unit to be converted into which unit ?

20 Inch3 3
m

Min S

Inch3 (2.54) 3 cm3 (1 m)3 1 min

= 5.46 * 10-6 m3/S
min Denominator
Numerator/ 1 inch 3
(100) cm
3
60 sec

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Potential Energy In physics, potential energy is the energy stored in

an object due to its position in a force field or in a
system due to its configuration

In physics, the kinetic energy of an object

Kinectic Energy
is the energy that it possesses due to its
motion

F= ma in FPS system you should use conversion Factor i.e.

1 / 32.174

K.E = ½ m v2

P.E= mgh

REVISION
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Lecture 2 : Moles, Density and Concentration
• What is a mole ?
• M. W = mass/ mole
• How to calculate M.W and mole fraction
• Density = mass/ volume , ρ
• Specific Volume= volume/mass, Ṽ= V/m
• Bulk Density= total mass of solids/total empty bed volume
(g/cm3)A (kg/m3)A (lb/ft3)A
• Specific Gravity of A =
(g/cm3)ref (Kg/m3)ref (lb/ft3)ref

Reference for Liquid is water= 1 g/cm3 = 62.4 lb/ft3

Reference for gas is air = 1 g/cm3

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Lecture 2 : Moles, Density and Concentration
Mole fraction : Individual Moles/ total moles
Mole %= mole fraction * 100
Mass fraction= Individual mass/ total mass

(g/cm3)A (kg/m3)A (lb/ft3)A

(g/cm3)ref (Kg/m3)ref (lb/ft3)ref

Reference for Liquid is water= 1 g/cm3 = 62.4 lb/ft3

Reference for gas is air = 1 g/cm3

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Lecture 2 : Average Molecular weight

Discuss how to calculate it?

Avg Molecular Weight= (mole fraction )A * (M.W) A + (mole fraction )B * (M.W) B

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Concentration : Concentration refers to the quantity of some substance per unit
volume (Mass per unit volume, Moles per unit volume, parts per million)

Problem : The current OSHA 8- hour limit for HCN in air is 10 ppm. A lethal dose of
HCN in air is ( from merck Index) 300 mg/Kg of air at Room
Temperature. How many mg HCN/kg air is 10 ppm? What fraction of the
lethal dose is 10 ppm.

Solution :

1 kg mol of air/ HCN mixture HCN 10 ppm Air

You can treat that 10 ppm as 10.00 g mol/ 106 gmol air because the amount of HCN is so small
when added when added to the air in the denominator

Thus, 10 ppm is
10 g mol HCN 10 gmol HCN
106 ( air +HCN) g mol 106 gmol air

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M W of HCN = 27.03

10 g mol 27.03 g 1 g mol air 1000 mg 1000 g air

HCN HCN HCN
= 9.32 mg
106 gmol 1 gmol 29 g air 1 g HCN 1 kg air HCN / kg
air HCN air

9.31
300
= 0.031

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10 g mol 27.03 g 1 g mol air 1000 mg 1000 g air

HCN HCN HCN
= 9.32 mg
106 gmol 1 gmol 29 g air 1 g HCN 1 kg air HCN / kg
air HCN air

9.31
300
= 0.031

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You purchase a tank with a volume of 2.1 ft3 . You pump the tank out, and add first
20 lb of CO2 and then 10 lb of N2 ? What is the Analysis of the final gas in the tank

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Temperature Measuring
Instruments

• Thermometer
• Thermocouple
• Thermistor
• Pyrometers

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Temperature
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TOPICS

• Pressure

• Chemical Equations and Its Stoichometery

• Limiting Reactant, Excess reactant and Selectivity and yield

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Pressure is defined as Force Per unit Area

P=F/A

Example : Cylinder full of water

Top Pressure
exerted by
atmosphere

Force
exerted
Bottom against the
pressure water
exerted by surface
water

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  density of

F
p   gh  p0
A

P= pressure at the bottom of the

column of the fluid
F= Force
A=Area
g= Acceleration due to gravity
h = height of the fluid column
fluid
p0= pressure at the top

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Example:
Suppose the column of mercury of area 1 cm2 and height of 50 cm . Calclulate
Pressure?

Solution :
We know that specific at 200 C and hence the density , essentially of Hg is
13.55 g/cm3. Thus, force can be calculated as
F= ma = ρV.a = ρ .A.h. a { Area* h (height)= Volume, a = accleartion due
to gravity}

F= 6.64 N. Pressure on a section of a plate covered by Mercury is given by

6.64 N (100 cm)2

= 66400 N/m2
1 cm 2
1m 2

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Calculation in American system: Here g is divided by gc value

Sometimes Pressure is also represented as head of the column . For example in

Inch of mercury.

Pressure at the base of the column is calculated as

i.e. p (in inch of Hg) = p0 (in inch of Hg) + h (in inch of Hg).

Suppose you want the measure pressure in a tank of water 2 ft down from the
surface as 404.4 inch H20 . What is the pressure 4 ft down from the surface
12 inch
P= 404 inch H20 + 2 ft 1 ft = = 428.92 inch
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Pressure Measurements

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1> If the Pressure connected to N2 connected is higher than the
atmosphere, its left leg (manometer) will have higher head and the
difference between left and right leg will denote Pressure Drop

2> Hydrostatic balance is achieved by the fluid

3> In case of vaccuum the fluid will rise on the vaccum side

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PRESSURE
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Pressure Terminology

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PRESSURE
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PRESSURE
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Pressure 29
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Pressure 30
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Pressure
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Pressure
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Pressure
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Pressure
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Pressure