Entropy second law of thermodynamics
Part of the weight of the piston is removed. Step 1 : the system is in contact with a high temperature reservoir. The gas is confined in a cylinder by a piston which has weight on top. The initial situation is specified by a volume V a, a pressure p a, and a temperature T a.
#Entropy second law of thermodynamics full
One full cycle consists of two isothermal and two adiabatic processes.
#Entropy second law of thermodynamics series
The performance of a refrigerator is specified by the coefficient of performance KĪn example of a series of processes which would create a reversible engine is the carnot cycle. " It is not possible for heat to flow from one body to another body at a higher temperature Another formulation of the second law of thermodynamics states that Thus, there are no perfect engines.Ī refrigerator is a device that causes heat to flow from a cold place to a warm place. However, the second law of thermodynamics clearly states that it is impossible to change heat completely into work. The first law of thermodynamics tells us that the net work done per cycle therefore must equal the net heat transferred per cycle:Ī measure of the performance of an engine is its thermal efficiency e, which is defined as the ratio of the work done per cycle and the heat absorbed per cycleĪ 100% efficiency will be obtained if and only if Q C = 0. Since it has the same temperature at the beginning and at the end of the cycle, its internal energy did not change. After one complete cycle the gas in the system returns to its original state. The basic operation cycles of an engine consist of extracting heat from a reservoir, performing work, and supplying heat to another reservoir (see Figure 19.1). In that case, the net work and heat will be zero. In order to return the gas to its internal state we need to do work and extract heat from the system. However, in the process we have also changed the state of the gas. This shows that we have converted all extracted heat into work. From the first law of thermodynamics we conclude that Since the internal energy of the gas only depends on its temperature, the internal energy of the gas will not change. Its volume will increase while its temperature remains constant. The gas is permitted to expand by removing some weight of the piston. The gas is in contact with a heat reservoir with temperature T. Let us look at an ideal gas confined by a piston in a volume V i. " It is not possible to completely change heat into work with no other change taking place " Although work can be completely changed into heat, the reverse is not true ( second law of thermodynamics). The heat is used to expand the gas, and lift the piston. In the engine of a car the heat is generated by the combustion of an air-gas mixture. Second Law of ThermodynamicsĪn engine changes heat into work. Entropy and the Second Law of Thermodynamics 19.1.