南昌大学材料热力学答案

氧化亚铜（氧化亚铜）正被在一炉中于1000K降低氢， （一）写为氧化亚铜的减少一摩尔化学反应

（二）有多少热量释放或每摩尔吸收反应的？鉴于热量和状态量的热量是否演变（放热反应）或吸收（吸热反应）

DATA: heat of formation of 1000K in cal/mol Cu2O=-41900 H2O=-59210 solution

Cu2O?H2?Cu?H2O?H?59210?41900?17310(cal/mol),exothermic reaction

1.14(a) what is the enthalpy of pure, liquid aluminum at 1000K? (b) an electric resistance furnace is used to melt pure aluminum at the rate of 100kg/h. the furnace is fed with solid aluminum at 298K. The liquid aluminum leaves the furnace at 1000K. what is the minimum electric powder rating (kW) of furnace.

DATA : For aluminum : atomic weight=27g/mol, Cp,s=26(J/molK), Cp,L=29(J/molK), Melting point=932K, Heat of fusion=10700J/mol Solution?26?(932?298)?29?(1000?932)?10700?27184(J/mol)

298932Hl,1000??CP,SdT??P?9321000SCP,LdT?HL271841?1000??279.7(W)?0.28(kW)2736001.15 A waste material (dross from the melting of aluminum) is found to contain 1 wt% metallic aluminum. The rest may be assumed to aluminum oxide. The aluminum is finely divided and dispersed in the aluminum oxide; that is the two material are thermally connected.

If the waster material is stored at 298K. what is the maximum

temperature to which it may rise if all the metallic aluminum is oxidized by air/ the entire mass may be assumed to rise to the same temperature. Data : atomic weight Al=27g/mol, O=16g/mol, Cp,s,Al=26(J/molK), Cp,s, Al2O3=-1676000J/mol Solution;

11676000??27?2?T?302(K)T?600(K)1?16?1.5?27?9927?104??T102Al2O3=104J/mol, heat formation of

1.16 Metals exhibit some interesting properties when they are rapidly solidified from the liquid state. An apparatus for the rapid solidification of copper is cooled by water. In the apparatus, liquid copper at its melting point (1356K) is sprayed on a cooling surface, where it solidified and cools to 400K. The copper is supplied to the apparatus at the rate of one kilogram per minute. Cooling water is available at 20℃, and is not allowed to raise above 80℃. What is the minimum flow rate of water in the apparatus, in cubic meters per minute?

DATA; for water: Cp=4.184J/g k, Density=1g/cm3; for copper: molecular weight=63.54g/mol

Cp=7cal/mol k, heat of fusion=3120 cal/mol

QCopper/min?[3120?7?(1356?400)]?Solution:Q100063.54?minWater/min?1(80?20)V

V?2.573?10?3(m3/min)1.17 water flowing through an insulated pipe at the rate of 5L/min is

to be heated from 20℃ to 60℃ b an electrical resistance heater. Calculate the minimum power rating of the resistance heater in watts. Specify the system and basis for you calculation. DATA; For water Cp=4.184J/g k, Density=1g/cm3

Solution: W?4.184?(60?20)?5?1000?13947(W)

601.18 The heat of evaporation of water at 100℃ and 1 atm is 2261J/mol

(a) what percentage of that energy is used as work done by the vapor?

(b)if the density of water vapor at 100℃ and 1 atm is 0.597kg/m3 what is the internal energy change for the evaporation of water?

P?V?101325?Solution:

%?3101 ?7.6"61?18?U?W?Q??3101?2261?18?37597(J/mol)373?0.0224?3101(J/mol)2731.19 water is the minimum amount of steam (at 100℃ and 1 atm pressure) required to melt a kilogram of ice (at 0℃)? Use data for problem 1.20 Solution

m(2261?4.18?100)?1000?334,m?125(g)

1.20 in certain parts of the world pressurized water from beneath the surface of the earth is available as a source of thermal energy. To make steam, the geothermal water at 180℃ is passed through a flash evaporator that operates at 1atm pressure. Two streams come out of the evaporator, liquid water and water vapor. How much water

vapor is formed per kilogram of geothermal water? Is the process reversible? Assume that water is incompressible. The vapor pressure of water at 180℃ is 1.0021 Mpa( about 10 atm) Data: CP,L=4.18J/(g k), CP,v=2.00J/(g k), △HV=2261J/g, △Hm=334 J/g Solution:

(2261?2?80?4.18?80)x?4.18?80?(1000?x),x?138(g)

irreversibleThe problems of the second law

2.1 The solar energy flux is about 4J cm2/min. in no focusing collector the surface temperature can reach a value of about 900℃. If we operate a heat engine using the collector as the heat source and a low temperature reservoir at 25℃, calculate the area of collector needed if the heat engine is to produce 1 horse power. Assume the engine operates at maximum efficiency.

太阳能通量为约4J平方厘米/分钟。在没有聚焦集电极的表面温度可达到约900℃的值。如果操作使用集电极作为热源和低温贮存器的热机，在25℃，计算所需集电极的面积如果与热机是产生1马力。假设在发动机工作在最大效率。 Solution