Gases, Vapors, Liquids, and Solids

1
Gases, Vapors, Liquids, and Solids As
Engineers, we face processes, operations that
require knowledge of properties such as P, T,
V, (these can be measured) H,U,S, (these are
calculated from measured ones) Some Data for
properties of pure substances and mixtures are
available But not all data are available
Dr. F. Iskanderani ChE
201 Spring
2003/2004
2

• gt we need to predict the data required.
• Predictions
• some predictions have theoretical background
• some are empirical

Dr. F. Iskanderani ChE
201 Spring
2003/2004
3
THE IDEAL GAS LAW 1) For pure substances PVnRT R
can be calculated R PV/nT at standard
conditions Standard conditions are P1atm,n
1kg mole, T273.15K V22.415m3 Any equivalent
units can be used to generate an R value at these
units
Dr. F. Iskanderani ChE
201 Spring
2003/2004
4
THE IDEAL GAS LAW For a gas changing from state
1 to state 2 P1 V1n1RT1 (1) and
P2 V2n2RT2 (2) Divide equation
1 by equation 2
Dr. F. Iskanderani ChE
201 Spring
2003/2004
5
THE IDEAL GAS LAW GAS Density is
mass/Volume nm/Mwt gt ? m/V n x Mwt

V (PVnRT Thus n/V P/RT) Therefore ? P x
MWt
RT
Dr. F. Iskanderani ChE
201 Spring
2003/2004
6
2) Ideal Gas Mixtures a- Dalton's Law (of
partial pressures)
N2 gas
H2 gas
O2 gas
O2 N2 H2
V is fixed
V is fixed
V is fixed
V is fixed
pN2 V nN2RT pH2 V nH2RT pO2 V nO2RT
ptot V ntotRT Or in general pi V
niRT
Dr. F. Iskanderani ChE
201 Spring
2003/2004
7
pi ptot ni/ntot ptot x yi THUS
p1p2p3 .. .. ptot(y1 y2 y3 ..)
ptot PARTIAL PRESSURE Pressure that would be
exerted by a single component in a gaseous
mixture if it existed alone in the same volume
occupied by the mixture at the same T of the
mixture.
Dr. F. Iskanderani ChE
201 Spring
2003/2004
8
b- Amagat's Law (of partial volumes) P is fixed.
T is fixed
O2 gas
N2 gas
H2 gas
O2 N2 H2
V is variable
P VN2 nN2RT P VH2 nH2RT P VO2 nO2RT P
Vtot ntotRT Or in general P Vi
niRT
Dr. F. Iskanderani ChE
201 Spring
2003/2004
9
Vi Vtot ni/ntot Vtot x yi THUS
V1V2V3 .. .. Vtot(y1 y2 y3 ..)
Vtot PARTIAL VOLUME Volume that would be
occupied by a single component in a gaseous
mixture if it is put alone under the same (total)
pressure of the mixture at the same T of the
mixture.
Dr. F. Iskanderani ChE
201 Spring
2003/2004
10
Example A gas mixture contains 14 CO2, 6O2
and 80 N2 at 400oF and 750 mmHg. Calculate the
partial pressure of each component. If the total
volume of container is 2 ft3, calculate the
partial volume of each component.
Dr. F. Iskanderani ChE
201 Spring
2003/2004
11
Material balance involving gases Example1 Find
F in m3/min
0.0917 m3/min of CO2 at 7oC and 131 KPa
Vol
CO2 3.4
Others 96.6
100
A
Vol
CO2 1.2
Others 98.8
100
F
P

At 15oC and 105 KPa
At 15oC and 105 KPa
Dr. F. Iskanderani ChE
201 Spring
2003/2004
12
Example 2 10 of CO does not burn. Find the ft3
of air supplied per ft3 of entering gas. Find the
ft3 of flue gas at given conditions per ft3 of
entering gas
40 excess Air at 70oF and 29.4 in Hg
CO2
O2
CO
H2O
N2
Mole
CO2 6.4
O2 0.1
CO 39.0
H2 51.5
CH4 0.6
N2 2.1
COMBUSTION CHAMBER
At 400oF and 29.4 in Hg
At 90oF and 35 in Hg