The Laws of Thermodynamics.ppt

Chapter 12 The Laws of Thermodynamics Principles of Thermodynamics Energy is conserved FIRST LAW OF THERMODYNAMICS Examples: Engines (Internal - Mechanical) Friction (Mechanical - Internal) All processes must increase entropy SECOND LAW OF THERMODYNAMICS Entropy is measure of disorder Engines can not be 100% efficient Converting Internal Energy to Mechanical Example Solution Quiz Review Some Vocabulary Example Example Example Work from closed cycles Work from closed cycles Work from closed cycles Example One More Example Solution Solution Solution Continued Example Give Quiz Entropy Measure of Disorder of the system(randomness, ignorance) S = kBlog(N) N = # of possible arrangements for fixed E and Q Entropy Total Entropy always rises! (2nd Law of Thermodynamics) Adding heat raises entropy Why does Q flow from hot to cold? Efficiencies of Engines Consider a cycle described by:W, work done by engineQhot, heat that flows into engine from source at ThotQcold, heat exhausted from engine at lower temperature, Tcold Efficiency is defined: Carnot Engines Idealized engine Most efficient possible Carnot Cycle Example Refrigerators Heat Pumps Example Solution Give Quiz Work done by expansion A cylinder of radius 5 cm is kept at pressure with a pistonof mass 75 kg.  a) What is the pressure inside the  cylinder? b) If the gas expands such that the  cylinder rises 12.0 cm, what work was  done by the gas? c) What amount of the work went into  changing the gravitational PE of the  piston? d) Where did the rest of the work go? Given: M =75, A = p?0.052, Dx=0.12, Patm = 1.013x105 Pa a) Find Pgas = 1.950x105 Pa b) Find Wgas = 183.8 J c) Find Wgravity = 88.3 J d) Where did the other  work go? Compressing the outside air A massive copper piston traps an ideal gas as shown to the right. The piston is allowed to freely slide up and down and equilibrate with the outside air. Pick the most correct statement? A. The pressure is higher