The work done by a gas at constant pressure is W = p dV, where W is work, p is pressure and dV is change in volume.įor non-constant pressure, the work can be visualized as the area under the pressure-volume curve which represents the process taking place. When work is done by a thermodynamic system, it is usually a gas that is doing the work.
The internal energy may be increased by transferring energy to the object from a higher temperature (hotter) object - this is called heating. An object does not possess "heat" the appropriate term for the microscopic energy in an object is internal energy. Heat may be defined as energy in transit from a high temperature object to a lower temperature object. If the water were tossed across the room, this microscopic energy would not necessarily be changed when we superimpose an ordered large scale motion on the water as a whole. But on the microscopic scale it is a seething mass of high speed molecules. For example, a room temperature glass of water sitting on a table has no apparent energy, either potential or kinetic. It is separated in scale from the macroscopic ordered energy associated with moving objects it refers to the invisible microscopic energy on the atomic and molecular scale. Internal energy is defined as the energy associated with the random, disordered motion of molecules. It is used extensively in the discussion of heat engines. The first law makes use of the key concepts of internal energy, heat, and system work. open systems: exchange of both matter and energy.
closed systems: no exchange of matter but some exchange of energy.isolated systems: no exchange of matter or energy.The first law is the starting point for the science of thermodynamics and for engineering analysis.īased on the types of exchange that can take place we will define three types of systems: The potential energy stored in the chemical bonds of the molecules.The kinetic energy associated with the motions of the atoms.The energy transfer between different systems can be expressed as: To work out thermodynamic problems we will need to isolate a certain portion of the universe, the system, from the remainder of the universe, the surroundings. However, energy can be transferred from one part of the universe to another. The 1st Law of Thermodynamics tells us that energy is neither created nor destroyed, thus the energy of the universe is a constant.
0 kommentar(er)
