Surroundings energy flow

In this text the same conventions also apply to the flow of work. If the system does work on the surroundings (energy flows out of the system), w is... 

System and Surroundings Energy Flow to and from a System Heat and Work Energy Conservation Units of Energy State Functions... 

In this text the same conventions apply to the flow of work. If the system does work on the surroundings (energy flows ouf of the system), w is negative. If the surroundings do work on the system (energy flows into the system), w is positive. We define work from the system s point of view to be consistent for all thermodynamic quantities. That is, in this convention the signs of both q and w reflect what happens to the system thus we use AE = q + w. 

Schematic diagrams showing energy flows that accompany reactions, (a) When a reaction releases energy, the change in energy (A S ) is negative for the chemical reaction and positive for the surroundings, (b) When a reaction absorbs energy.

Figure 6-17 illustrates a constant-volume calorimeter of a type that is often used to measure q for combustion reactions. A sample of the substance to be burned is placed inside the sealed calorimeter in the presence of excess oxygen gas. When the sample bums, energy flows from the chemicals to the calorimeter. As in a constant-pressure calorimeter, the calorimeter is well insulated from its surroundings, so all the heat released by the chemicals is absorbed by the calorimeter. The temperature change of the calorimeter, with the calorimeter s heat capacity, gives the amount of heat released in the reaction. 

To summarize the total energy flow in space surrounding the conductors has two components as follows ... 

Figure 5 shows that almost all that great EM energy flow—pouring out of the terminals of the generator or battery and out through the surrounding space... 

Figure 4. Poynting (caught) energy flow contours surrounding a transmission line.

The principle of conservation of energy plays a fundamental role in thermodynamics and is. therefore, also called the first law of thermodynamics. In ils mosl general form il postulates ihc existence of a function of stale, called the internal energy of the system V. such that its chnnge per unit lime is equal lo some flow, called the energy flow from the surroundings. 

So far, we have not seen how to calculate the work done by a system except for the simple case of raising a weight. At this point, we start to consider real chemical reactions taking place in containers of various kinds and begin to explore how energy flows from the reaction system into the surroundings, or vice versa. 

Heat can be defined as a portion of the total energy flow across a system boundary and is caused by a temperature difference between the system and the surroundings. Heat can be exchanged by conduction, convection and/or radiation. We can evaluate heat transfer by use of the energy balance, which will be discussed later. 

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