PHY 182 1st Edition Lecture 9 Outline of Last Lecture I. Heat Capacity of GasesII. Heat Capacity of SolidsIII. Molecular SpeedsOutline of Current Lecture I. Thermal Interactions and Heat EnginesII. 2nd Law of ThermodynamicsIII. EntropyCurrent LectureThermal Interactions and Heat Engines- When two objects have reached thermal equilibrium, it means that they have the same temperature and the same average translational kinetic energy.- A heat engine is a device that turns heat into work.- The process that a heat engine performs is a cyclical process, which means that the change in thermal energy is zero. (ΔEth=0 means that the system ends in the same thermalstate as when it began the process.)- When doing a problem involving heat engines, we will look at work from the perspective of the system. This means that positive work is defined as work done by the system. In the case of the heat engine, Q=W.- It is not possible for a heat engine to have 100% efficiency. This means that Qc (the heat given off by the system) will never be zero.2nd Law of Thermodynamics- The second law of thermodynamics provides and explanation for why thermodynamic processes proceed in a certain way.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Remember that the first law of thermodynamics only states that the change in thermal energy is equal to work + heat, it does not tell you which direction heat will flow.- On the atomic scale, you can't distinguish if a process is happening forwards or backwards (i.e. there is no concept of time).Entropy- Entropy is a state variable; it is the measure of the "disorder" of a system.- The entropy of a closed system will never decrease. This is how we know the way in which a process will naturally occur.- Theoretically, the entropy of a system could decrease but it is a statistical
View Full Document