CHE 203 – Chemical Engineering Thermodynamics I
2010 - 2011 (102)
HW#7
Due date: Saturday, May 7, 2011
Q1.
A continuous chemical vapor deposition (CVD) reactor is used to deposit thin and
uniform silicon dioxide film. The following CVD process involves the reaction between
silane and oxygen at very low pressure:
SiH4 ( g )  O2 ( g )  SiO2 ( s )  2H 2 ( g )
The feed gas, which contains oxygen and silane in a ratio (8.00 mol O2 /mol SiH 4 ), enters
the reactor at 298 K and 3.00 torr absolute. The reaction products emerge at 1375 K and
3.00 torr absolute. All of the silane in the feed is consumed.
1. Taking a basis of 1 m 3 of feed gas, calculate the moles of each component of the
feed and product mixtures and the extent of reaction,  (mol).
2. Calculate the standard heat of the silane oxidation reaction (kJ/mol). Then, taking
the feed and product species at 25°C as references, prepare an inlet—outlet
enthalpy table and calculate and fill in the component amounts (mol) and specific
enthalpies (kJ/mol).
3. Calculate the required rate of heat transfer (kJ) to or from the reactor (state which
it is).
Data:
Ĥ 
Ĥ 
0
f
SiH 4 ( g )
0
f
SiO2 ( s )
 61.9 KJ / mol
 851 KJ / mol
C 
[KJ/(mol.K )]  0.01118  12.2 * 10 -5 * T - 5.548 * 10 -8 * T 2  6.84 * 10 -12 * T 3
C 
[KJ/(mol.K )]  0.04548  3.646 * 10 -5 * T - 1.009 * 10 3 / T 2
p SiH ( g )
4
p SiO ( s )
2
Q2.
Normal heptane is dehydrocyclicized to toluene and hydrogen in a continuous vaporphase reaction:
C7 H 16  C 6 H 5 CH 3  4H 2
Pure heptane at 400 °C is fed to the reactor. The reactor operates isothermally at 400 °C
and the reaction goes to completion. The average heat capacity of n-heptane between
25°C and 400 °C is 0.2427KJ/(mol. °C).
Calculate the required heat transfer to or from the reactor in KJ using the heat of
formation method.
Q3.
Ammonia is oxidized with air to form nitric acid oxide. The following reactions occur:
4 NH 3  5O2  4 NO  6 H 2 O
2 NH 3 
3
O2  N 2  3 H 2 O
2
The reactants data:
100 mol NH3(g)/min at 25°C and 8 bar.
900 mol air/min (21% O2 and 79 % N2) at 150 °C and 8 bar.
The products are gases at 700°C and 8 bar:
90 mol NO/min
150 mol H2O(v)/min
716 mol N2/min
69 mol O2/min