Test 2013, questions and answers PDF

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Example Questions Chemical Engineering Thermodynamics 1. A fuel consisting of 75 methane (CH4) and 25 ethane (C2H6) enters a furnace with excess air at 250C. If J per mole of fuel is transferred as heat to boiler tubes from the furnace, at what temperature does the flue gas leave the furnace? (9 mar...

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Example Questions Chemical Engineering Thermodynamics

1. A fuel consisting of 75 mol% methane (CH4) and 25 mol% ethane (C2H6) enters a furnace with 80% excess air at 250C. If 800000 J per mole of fuel is transferred as heat to boiler tubes from the furnace, at what temperature does the flue gas leave the furnace? (9 marks) Assume complete combustion of the fuel. Reactions to consider: CH4 (g) + 2O2 (g)

CO2 (g) + 2H2O (g)

C2H6 (g) + 3.5O2 (g)

2CO2 (g) + 3H2O (g)

Heat of formation: CH4 = -74520 J/mol C2H6 = -83820 J/mol CO2 = -393509 J/mol H2O = -241818 J/mol Specific Heat (Cp) : CH4 = 35.06 J/mol K C2H6 = 52.95 J/mol K CO2 = 37.13 J/mol K H2O = 35.46 J/mol K O2 = 29.41 J/mol K N2 = 29.12 J/mol K Here, Q = ∆H for the complete process. 2. One mole of an ideal gas is compressed isothermally but irreversibly at 1300C from 2.5 bar to 6.5 bar in a piston/cylinder device. The work required is 30% greater than the work of reversible, isothermal compression. The heat transferred from the gas during the Q2 is not compression flows to a heat reservoir at 250C. Calculate the entropy changes of the gas, the relevant to Test heat reservoir, and ∆Stotal. (6 Marks)

1 2016

∆S = Cp * ln(T2/T1) - R* ln(P2/P1) Also, Work done for reversible, isothermal compression = R*T* ln(P2/P1) (R = 8.314 J/mol K)

Faculty of Science and Engineering Department of Chemical Engineering

Chemical Engineering Thermodynamics 223 Test 1 (15 marks) Friday, 23rd August 2013

1. A system is taken through a series of processes as a result of which it is restored to the initial state. The work and heat interactions for some of the processes are measured and they are as given below: Process W (kJ) Q(kJ) ∆U (kJ) 1-2 120 220 2-3 -130 220 3-4 -230 4-1 320 70 Complete the table and determine the net work done and net heat interaction (No marks will be provided if steps are not shown correctly). (5 marks)

2. One mole of an ideal gas (PV/T = constant), initially at 30°C (303.15K) and 1 bar, is changed to 130°C (403.15K) and 10 bar by two mechanically reversible processes: (a) The gas is first heated at constant volume until its temperature is 130°C (403.15K); then it is compressed isothermally until its pressure is 10 bar [5 marks] (b) The gas is first heated at constant pressure until its temperature is 130°C (403.15K); then it is compressed isothermally to 10 bar [5 marks] Calculate Q, W, ΔU, and ΔH in each case. Given: R = 8.314 J mol-1 K-1

C P = (7/2) R

C V = (5/2) R

Question 1 Process 1 to 2 2 to 3 3 to 4 4 to 1

Question 2

W (kJ) 120 350 -230 320 560

Q(kJ) 220 -130 -400 -250 -560

dU (kJ) 340 220 -630 70 0...