ChE 471 - Washington University in St. Louis



ChE 471 Homework Set 1 2008

(Due Friday, September 5)

1. Express each of the reaction systems listed below ( a to c) in the form:

[pic]

and identify all Ajs, S and [pic]

a) CaCO3 = CaO + CO2

b) 3H2 + N2 = 2NH3

c) NC(CH2)4 CN + 4H2 = H2N (CH2)6 NH2

2. For the reaction

C6H6 + C12 = C6H5 C1 + HC1

and the molar feed rate of

[pic]

a) Find the limiting reactant.

b) Calculate the molar flow rates and mole fractions at the outlet of all species

at 99% conversion of the limiting reactant.

3. Consider steam reforming of natural gas

CH4 + H2O = 3H2 + CO

at 1300oK and P = 1 atm. Assume constant pressure and temperature.

Given:

Feed rate: 0.01 kmol CH4/s; 0.02 kmol H2O/s

Conversion of limiting reactant is 90% of the equilibrium conversion.

Calculate:

a) The equilibrium conversion and actual conversion.

b) Q/Qo i.e the ratio of the exit and feed volumetric flow rate.

c) Molar concentration of all species at the exit.

d) Equilibrium conversion at 1300 K and 10 atm. Do you expect it to be higher or lower than at 1 atm?

4. Reaction A + B = R proceeds in the gas phase at constant pressure and temperature.

The feed contains CAo = CBo = CIo = 0.01 (mol/m3) where I stands for gaseous

inert. Find CA and CB and CR when A is 95% reacted i.e xA = 0.95.

5. The rate of reaction of SO3 at a given set of conditions is found to be:

0.01 (kmol/m3 reactor s). The reaction is [pic]

a) Find the rates of reaction of SO2 and O2 at these conditions.

b) If the catalyst bulk density is 1.2 (g catalyst/cm3 reactor); catalyst pellet

density is 2.1 (g/cm3); catalyst surface area is Sg = 80 (m2/g) and bed

porosity is 0.45 (m3 voids/m3 reactor) find the rate of reaction

expressed per

i) unit volume of reaction mixture or voids

ii) unit volume of catalyst

iii) unit catalyst area

iv) unit catalyst mass

6. We have shown that for a single gas phase reaction [pic] conducted at constant temperature and pressure the volume changes with reaction progress as [pic].

Derive the relationship for V/Vo (volume change) for ideal gases at P, T constant when a set of R multiple reactions occurs in the system

[pic]

Recall that now

[pic]

where Xi is the extent of the i-th reaction.

7. Consider the following reaction system and assume ideal gas behavior:

CH4 + H2O = CO + 3H2

CO + H2O = CO2 + H2

Initially you have a mixture of methane, CH4, and water vapor, H2O in a 1:1 molar ratio with no CO, CO2 or inerts present. After all of the water has reacted you find CO/CO2 at a 3 to 1 ratio.

a) Find the mole fractions of all the species present at the end of reaction.

b) Find the V/Vo for this system when reaction ends.

Hint: Assume a basis. Use the formula suggested in problem 1 for calculating the number of moles and from the information given find the extent of each reaction. Recall that [pic].

8. Solve the following problems from Chapter 1in the textbook

:

a) Problem 1,

b) Problem 3.

9. On a separate sheet of paper write down reaction system(s) or process(es) involving chemical reactions that you would like to learn more about. Be specific as much as possible.

Please, list your name on the top of this sheet and submit it separately. Credit will be given for submitting this.

Thank you for your cooperation.

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