MAE 115 – Applied Engineering Thermodynamics
Examination #1
2023
Conceptual Short Answer (25 points):
1. Answer the following questions with a single short sentence, expression, or word.
a. For a given molecule, what type of energy does hf(o) represent?
b. State the direction of energy flow in a system to produce the following molecules:
a. Acetylene (C2H2 , hf(o) = +226,730 KJ/Kmol)
b. Propane (C3H6, hf(o) = −103,850 KJ/Kmol)
c. Hydrogen (H2, hf(o) = 0 KJ/Kmol)
c. Will a mixture of gases always reach chemical equilibrium quickly?
d. You have Kp data for the following reaction: H2 + ½ O2 ↔ H2O. If the stoichiometric coefficients of this reaction are doubled, how can you use the original Kp data?
e. Using the table to the right, at approximately what temperature will the forward reaction occur as frequently as the reverse reaction?
H2 ↔ 2 H
Temperature (K)
ln(KP)
2200
-2.534
2400
-1.516
2600
-0.609
2800
0.202
3000
0.934
3500
2.486
4000
3.725
4500
4.743
5000
5.590
General Thermodynamic Properties (20 points):
2. Prove that the enthalpy of an ideal gas is a function of temperature only.
Recall:
Combustion (40 points):
3. A mixture of 1 kmol Methane (CH4) and 80% excess air, both originally at 350 K, are combusted at a constant pressure of 1 atm
Determine the following:
(a) The balanced chemical reaction if complete combustion occurs (b) The equivalence ratio φ
(c) Using the table below, calculate how much energy is present in the reactants only
(d) You need t代 写MAE 115 Applied Engineering Thermodynamics 2023 Examination #1Java
o calculate the adiabatic flame temperature for this mixture. You’re first
temperature guess produces a total combustion products enthalpy of -40,000 kJ/kmol. Based on the reactant enthalpy calculated in (c), should your next temperature guess be higher or lower?
(e) If combustion were incomplete, and CO existed in the products, what system of equations (neglecting the first law for a reacting system) would be used to solve for the concentration of products? Assume the only dissociation to create CO is the following the equilibrium reaction: CO2 ↔ CO + ½ O2.
(f) If the air and methane mixture were initially heated to 600 K before any chemical
reaction occurred, would the adiabatic flame temperature increase, decrease, or remain the same? Provide a one sentence explanation for your answer.
(g) Would the adiabatic flame temperature increase or decrease if the combustion occurred at constant volume? Provide a one sentence explanation for your answer.
Species
Enthalpy of formation, hfo (kJ/kmol)
Enthalpy at 298 K (kJ/kmol)
Enthalpy at 350 K (kJ/kmol)
CH4
-74,850
11,744
13,824
O2
0
8,682
10,213
N2
0
8,669
10,180
Mixtures (15 points):
4. An insulated rigid tank contains a gas mixture. The gas mixture consists of 30 percent hydrogen, 40 percent nitrogen, and 30 percent Argon by volume. Determine the heat addition per kg required to raise the temperature of the mixture by 100 K. Assume constant specific heats.
Species
CP (kJ/kgK)
CV (kJ/kgK)
MW (kg/kmol)
N2
1.039
0.743
28
H2
14.307
10.183
2
Ar
0.5203
0.3122
40
WX：codehelp
