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1、2-1.Please explain the following thermodynamic terms:,1).internal energy( p2-2 L1-3,L6-7) Answer:Internal energy is the energy of the molecules making up the substance, including kinetic energy and potential energy. 2). closed system(P2-3, para5, L1-3); Answer:If the boundary of a system does not pe
2、rmit the transfer of matter between the system and surroundings,the system is said to be closed,and its mass is necessarily, the system is said to be closed.,3). state functions(p.2-5, L.13-17); Answer:These properties do not depend on the past history of the substance or on the path it has before o
3、r on the path it has followed in reaching a given state.They depend only on the present conditions. 4).critical point(p.3-1, L.9-11); Answer: The coordinates of this point are called the critical pressure Pc and the critical temperature Tc.These represent the highest temperature and temperature at w
4、hich a pure material can exist in vapor-liquid equilibrium.Homogeneous fluids are normally divided into two classes, liquids and gases. However, the distinction cannot always be sharply drawn, because the two phases become indistinguishable at what is called the critical point .,5).ideal gas(p.3-8,
5、para2,L6-10); Answer: Their actual volume becomes infinitesimal compared with the total volume cccupied by the gas,and the intermolecular forces of attraction approach zero.A gas which meets these conditions is known as an ideal gas. 6).compressibility factor(p.3-9, L.11). Answer: The ration PV/RT i
6、s called the compressibility factor,2-2 Give the statement and formulation of the first law of thermodynamics(P2-2,L25-26),Answer: 1.The first law of thermodynamics may be stated formally in many ways.one of these is as follows:the total quantity of energy is constant,and when energy disappears in o
7、ne form it appears simultaneously in other forms 2.（Energy of the system）+(energy of surroundings)=0,2-3 What is the difference between the state function and work or heat?(p2-5,2-6),Answer:1. State function are properties of the system,while work and heat are not state propertities,they are depende
8、d on the path followed. 2.The values of state function can always be represented by points on a graph,but work and heat can represented by points on a graph,rather are represented by areas,3.The differential of a state function is spoken of that as an infinitesimal chang in the property,and is not r
9、eferred to as a quantity.The differentials of heat and work are not referred to as changes, but are regarded as infinitesimal quantities of heat and work. 4.Another difference between state functions and heat or work follows from the fact that a state function represents an instantaneous (瞬间的) prope
10、rty of a system and always has a value (有一确定值). Work and heat appear only when changes are caused in a system by a process, which requires time.,2-4.What are the necessary conditions for the steady state flow process?(p.2-12) Answer: The term steady state implies that conditions at all point in the
11、apparatus are constant with time. It means that all rates must be constant, and there must be no accumulation of material of energy within the apparatus over the period of time considered. Moreover, the total mass flow rate must be the same at all point along the path of flow of the fluid.,2-5.Pleas
12、e indicate in which condition that the expression of first law U = W Q or H = W Q can be used respectively? Answer: The expression ofH = W Q is used for a steady-state flow process, and the expression of U = W Q is used for a nonflow process. (p.2-14,upward 1st line; p.2-15,L.1-3),2-6.What is the wo
13、rd equilibrium denoting? Answer: Equilibrium is a word denoting a static condition, the absence of change. In thermodynamics it is taken to mean not only the absence of change but the absence of any tendency toward change on a macroscopic scale.(p.2-18,upward 7-10th line),2-7.What is the meaning of
14、a phase in thermodynamics?(p.2-20,L.4-5) Answer: A phase is a homogeneous region of matter. It is not necessary that a phase be continuous .,2-8.What are the characteristics of reversible process? Answer: In summary, a reversible process is frictionless; it is never more than differentially removed
15、from equilibrium; the driving forces are differential in magnitude; and the process can be reversed, leaving no more than an infinitesimal change in the system or surroundings. (p.2-26, upward 6-9th line),2-1 An insulated and nonconducting container filled with 9.07(kg)of water at 20 is fitted with
16、a stirrer.The stirrer is made to turn by lowering a weight having a mass of 22.68(kg). The local acceleration of gravity is 9.75(m)/(s2).The weight slowly falls a distance of 9.144(m)while turnning the stirrer.Assumig that all the work done by gravity on the weight is transferred to the water,determine:,2l 一装有20C9.07Kg水的隔离又不导热的容器,配备的搅拌器靠质量为22.6kg的重物下落 来带动。当地重力速度为9.75(m)/(s2)。当搅拌器转动时，重物缓慢下降9.144(m)，假设重力力对重物所作的功都传给了水，试确定，c水的最终温度(C)d使水恢复到原始温度需要移走的热量e下还各过程的总能量变化：(1)重物下降过程(2)使水冷却到原始温度的过程 3）统一考虑这两个过程,
