Chapter_5_Systems-processes-cycles

# Chapter_5_Systems-processes-cycles - Chapter 5 Systems...

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Chapter 5 – Systems, processes, and cycles: The language of thermodynamics In thermodynamics, the totality of the world is usually termed the universe , and is divided into two parts. 1. The system is the part of the universe in which we are particularly interested. 2. The rest of the universe is the surroundings . Separating the system from the surroundings is the system boundary (see Fig. 5.1). Fig. 5.1. The system, the surroundings, and the system boundary. Systems can be of three types, depending on what can pass through the system boundary. 1. If matter, heat, and work can pass through the system boundary, then the system is an open system . 2. If heat and work can pass through the boundary, but matter cannot, then the system is a closed system . 3. If neither matter, not heat, nor work can pass through the boundary, then the system is an isolated system . Properties of systems are sometimes divided into two types as follows. 1. Extensive properties : these depend on the mass of substance present, for example volume, the greater the mass of air, the greater will be the volume. 2. Intensive properties : these do not depend on the mass of substance present, for example pressure and temperature. Specific volume is defined as the volume per unit mass, and so must be an intensive property. Extensive properties are usually given an upper case symbol, for example V for volume. Intensive properties are usually given a lower case symbol, such as p for pressure, and v for specific volume. However, the use of T for the intensive property temperature is an exception to this rule. 36

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Processes and reversibility A process is a change in the system from one state to another. Hence the change in the pressure and temperature of a mass of ideal gas from ( p 1 , v 1 ) to ( p 2 , v 2 ) is a process. The state defined by ( p 1 , v 1 ) is the initial state of the system, and the state defined by ( p 2 , v 2 ) is the final state of the system. Processes can be divided into two types as follows: 1. Reversible processes : these can be reversed so that both the system and surroundings are returned to their original condition after the process and the reverse process have been carried out. 2.
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Chapter_5_Systems-processes-cycles - Chapter 5 Systems...

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