Download 기초물리화학 2001년 (담당: 장윤희)

기초물리화학 2001년 2학기 (담당: 장윤희)
중간고사
2001/11/7(수) 오후 7시
Hint: Atomic weight: H 1.0076, C 12.01, N 14.01, O 16.00, Ar 39.95
Unit conversion: 1 L = 1  103 m3, 1 kPa = 1  103 N m2, 1 V A s = 1 J
Constants: gas constant R = 8.31451 J K1 mol1
(Concept of moles)
1. What amount (that is, how many moles) of H2O molecules is present in 1.00 L of
water? (5 pts)
2. Calculate the mole fractions of N2, O2, and Ar in dry air at sea level, given that
100.0 g of air consists of 75.5 g of N2, 23.2 g of O2, and 1.3 g of Ar. (5 pts)
(Perfect and real gases)
3. (a) What is the "ideal (or perfect)" gas? (5 pts)
(b) In which condition real gases behave ideally (perfectly)? (5 pts)
4. Water vapor is at the pressure of P = 3.5 kPa and the temperature of T = 25oC.
(a) If this vapor behaved ideally, what would be its molar volume? (5 pts)
(b) However, when the molar volume was actually measured at this condition, it
was 18 L/mol, which was different from our expectation in (a). Based on the
results, find which interaction, repulsions or attractions, are dominant in the
intermolecular interactions between water molecules at this condition. (5 pts)
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5. The gas in an aerosol container exerts a pressure of 125 kPa at 18oC. What would
be the pressure of this can, if the temperature rose to 700oC. Assume that the gas
behaves perfectly and that the can does not melt up to 700oC. What lesson
regarding to safety can you draw from the result? (10 pts)
(1st law of thermodynamics: isothermal process versus adiabatic process; 10 pts)
6. A perfect gas is going to be subjected to an isothermal expansion or an adiabatic
expansion. The initial and the final volume is both processes will be the same.
(a) In which of these two processes will the gas have lower final temperature?
(b) In which of there two processes will the gas have lower final pressure?
(Answer and explain.)
(1st law of thermodynamics: Thermochemistry: energy and enthalpy; 20 pts)
7. We are going to measure the "heat content" of n-octane (n-C8H18(l), MW 114.23)
using a bomb calorimeter (constant-volume calorimeter) at 298.15 K.
(a) For a calibration of the calorimeter, an electric current of 1.27 A from a 12.5
V supply was passed for 157 s through a heating coil inside. The temperature
rose by 3.88 K. What's the heat capacity, Cv, of the calorimeter?
(b) In the same calorimeter, 114.23 g of n-octane was burned with an excess of
oxygen and converted completely into water and carbon dioxide gas. The
temperature rose by 8.51 K. How much heat was evolved out of this reaction?
(c) Based on the measurement in (b), calculate the standard enthalpy of
combustion, cHo, (in kJ/mol) of n-C8H18(l) and complete the
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thermochemical equation of this combustion reaction. Assume that the gases
involved are ideal.
(d) Based on the result in (c), calculate the standard enthalpy of formation, fHo, of nC8H18(l). Use the following data: fHo(CO2(g)) = 393.51 kJ mol1 and
fHo(H2O(l)) = 285.83 kJ mol1
(2nd law of thermodynamics and Gibbs free energy; 10 pts)
8. The rusting of iron is due to the following reaction:
4 Fe (s) + 3 O2 (g)  2 Fe2O3 (s).
(a) Using the data below, calculate Ho, So, and Go for the reaction at 25oC.
Data Compound fHo (kJ mol1) So (J K-1 mol1)
Fe (s)
0
27.28
O2 (g)
0
205.138
Fe2O3 (s)
-824.2
87.40
(b) Over what range of temperatures is the rusting of iron spontaneous? Assume
that gases are at 1 bar and that the values tabulated above are independent of
temperature.
(Phase transition and phase diagram; 15 pts)
9. 등산하기 좋은 계절입니다. 지금은 법으로 금지되었지만 예전에는 산에 올라
밥을 지어먹곤 했지요. 쌀이 익고 물 안의 나쁜 병균들이 죽으려면 물의 온도
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가 거의 100oC가 되어야 한다고 합시다. 오늘도 한 등산객이 라면 끓이는 데
쓰던 보통 남비를 몰래 가져와 밥을 짓고 있는데 아무래도 밥이 설익은 듯하
고 맛이 없습니다.
(a) 제대로 익은 밥을 위해서 여러분 같으면 이 등산객에게 어떻게 충고해주
겠습니까? 더 높이 올라가서 밥을 지으라고 권하겠습니까, 아니면 더 낮
은 곳으로 내려가서 밥을 지으라고 하겠습니까?
(b) 자리를 이동하지 않고 밥을 제대로 익히는 방법으로 어떤 게 있을까요?
(c) 이렇게 해서 맛있게 지어진 밥을 먹고 난 후 이 등산객이 그 이유를 듣고
싶어 한다면 여러분은 어떻게 이 현상을 설명하겠습니까? 물의 끓는점이
압력에 따라 어떻게 변하는 지가 설명의 요점이 되겠죠. 각 phase의 Gm과
T 사이의 관계 graph를 이용하거나, phase diagram의 liquid-vapor phase
boundary를 이용해서 설명해 보세요. 어느 쪽 설명이나 무방합나다. 다만
각각의 경우 graph나 boundary의 대략적 모양이 어떤 근거에서 나왔는지도
함께 설명하도록 하세요. 다행히도 이 등산객이 dGm = Vm dP  Sm dT 의 관
계식 정도는 알고 있다고 가정합시다.
(화학계 동향)
10. 2002년 노벨화학상이 어떤 분야에 돌아갔는지 간략하게 설명해보자. (5 pts)
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