May 09 2018

- the study of macroscopic properties of systems - the study of heat and its transformation to mechanical energy Temperature and Heat - thermodynamic equilibrium - where macroscopic properties are no longer changing - of two systems in thermal contact where heating one system changes the other - temperature - two systems have the same temperature if they are in thermodynamic equilibrium - it is the "intensity" of something - zeroth law of thermodynamics - two systems in thermodynamic equilibrium with a third system - are in thermodynamic equilibrium with each other - heat - energy being transferred from one object to another because of a temperature difference alone - it is the "amount" of something - internal energy - following heat transfer - the internal energy of an object has increased - heat capacity - the capacity of an object to absorb heat without changing temperature - amount of heat = heat capacity x change in temperature - heat transfer methods - conduction - heat transfer through direct physical contact - molecules in a hotter region collide with and transfer energy to those in an adjacent cooler region - convection - heat transfer by fluid motion - heated fluid becomes less dense and therefore rises - radiation - energy loss by emitting electromagnetic waves - objects are identically effective at emitting and absorbing radiation Thermal Behavior of Matter - matter responds to heating in a variety of ways in addition to changing temperature - other responses include changes of volume, pressure, and phase - gases - the macroscopic state of a gas in thermodynamic equilibrium - is determined by its temperature, pressure, and volume - all gases exhibit, to a very good approximation, the same relation among these quantities - ideal gas law - pressure x volume = temperature x molecules x constant - temperature is a measure of the average kinetic energy associated with random translational motion of the molecules - phase changes - heat of transformation - energy per unit mass required to change phase (solid to liquid to gas) - the reverse requires removing the same energy Thermodynamics - first law of thermodynamics - extends the conservation of energy to include internal energy - the change in the internal energy of a system - equals the net heat transferred to it and the net work done to it - second law of thermodynamics - heat engines convert internal energy to useful work in a reversible cycle - we cannot build a perfect heat engine - ideal efficiency = 1 - heat ratio = 1 - temperature ratio - entropy - the second law precludes converting heat to mechanical energy with perfect efficiency - entropy quantifies the loss of the quality of energy associated with energy transformations - the entropy of a closed system can never decrease