Heat and Work Two Forms of Energy Transfer

The total change in a system s internal energy is the sum of the energy transferred as heat and/or work  

CHAPTER 6 Thermochemistry Energy Flow and Chemical Change 

Energy Transfer as Heat Only For a system that does no work but transfers energy only as heat (q), we know that = 0. Therefore, from Equation 6.2, we have A = q + 0 = q. The two possibilities are  

Animation Energy Flow Online Learning Center 

Energy Transfer as Work Only For a system that transfers energy only as work (vr ), 7 = 0 therefore, AE = 0 -I- w = w. The possibilities are 

---

Energy Transfer to and from a System 190 Heat and Work Two Forms of Energy Transfer 190... 

List and define in your own words the three components of the total energy of a process system and the two forms of energy transfer between a system and its surroundings. State the conditions under which heat and work are positive. Convert an energy or power (en-ergy/tirae) expressed in any unit (e.g., J, dyne-cm, Btu, ft-lbf/h, kW, hp) to its equivalent in any other dimensionally consistent units. 

Thermodynamics studies two forms of energy transfer heat and work. Heat can be defined as transfer of energy caused by the difference in temperatures of two systems. Heat is transferred spontaneously from hot to cold systems. It is an extensive thermodynamic quantity, meaning that its value is proportional to the mass of the system. The SI (Systeme International de Unites) unit of the heat is the joule (J). The earlier unit of calorie is not in use any more. 

Once an appropriate choice of a system has been made, the concept of conservation of energy immediately becomes useful. Because we said that heat and work are the only possible forms of energy transfer, we can attribute the overall change in energy, E, of a system to these two components. Heat is commonly designated as q and work as iv, so we can write... 

Heat is a form of energy transfer caused by the difference in temperature between a system and its surroundings. Within thermodynamics, heat and work are two different forms of energy exchange between a system and its surroundings. 

We have attempted to introduce the concept of temperature as a thermodynamic parameter without any necessary reference to the concept of heat, although not necessarily avoiding that term. This was done by saying that diathermal walls exist tliat allow two bodies to interact energetically while excluding mechanical interaction and mass transfer. Since we limit forms of energy to work and heat (as discussed next), then if energy is transferred and work is eliminated, it follows that diathermal... 

Energy in the form of either work or of heat can be transferred to a thermodynamic system. As shown in the following, work and heat represent two fundamentally different forms of energy exchange. 

To derive the condition for thermodynamic equilibrium, we start with an isolated system consisting of two subsystems as shown in Figure 5.6. Subsystem A is the one of primary interest in that it is the one in which the chemical process is occurring. Subsystem B is a reservoir in contact with subsystem A in such a way that energy in the form of heat or work can flow between the two subsystems. If left alone, the system will come to equilibrium. Energy will be transferred between the subsystems so that the temperature and pressure will be... 

Energy is measured in terms of its ability to perform work or to transfer heat. Mechanical work is done when a force / displaces an object by a distance d w =/ x d. The basic unit of energy is the joule. One joule is the amount of work done when a force of 1 newton acts over a distance of 1 m thus 1 J = 1 N-m. The newton is the amount of force required to accelerate a 1-kg mass by 1 m/sec2, so the basic dimensions of the joule are kg m2 s 2,Thc other two units in wide use, the calorie and the BTU (British thermal unit), are defined in terms of the heating effect on water. Because of the many forms that energy can take, there are a correspondingly large number of units in which it can be expressed. A few of these are summarized in Table 1. 

---