Lecture 1

Lecture 1 - Thermodynamics is a funny subject. The...

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Unformatted text preview: Thermodynamics is a funny subject. The first 6me you go through the subject, you don’t understand it at all. The second 6me you go through it, you think you understand it, except for one or two small points. The third 6me you go through it, you know you don’t understand it, but by that 6me you are so used to the subject that it doesn’t bother you any more.  ­ Arnold Sommerfeld (1868 ­1951) What is Thermodynamics? •  Thermodynamics deals with energy content and its flow. •  Thermodynamics concerns with heat and its connec6on to other forms of energy. •  Thermodynamics is the study of the connec6on between heat and work and the conversion of one into the other. Why To Study Thermodynamics? •  Thermodynamics are used everywhere. Any situa6on where energy transfer is desirable, thermodynamic principles are applied. The car engines use heat to work, power plants transfer heat from some hot source to heat water into electricity. A refrigerator converts work into hea6ng and cooling. •  Thermodynamics is also used in designing chemical reac6ons •  Human bodies also apply the principles of thermodynamics. Human respiratory systems, skin, mouths, tongues, and other specialized organs and systems apply thermodynamics to regulate and maintain internal temperature in a wide range of ambient condi6ons. •  Understanding larger issues such as global warming. As living and non ­ living things go through their life cycles, and eventually into a state of decay, there is a dissipa6on of energy in the form of heat. Not all of that heat can be recycled into the system (the earth and everything on it). Greenhouse effect—trapping of solar energy by CO2. Forms of Energy & Their Interconversion •  Thermal (energy due to mo6ons of atoms/molecules) •  Electrical (Movement of electron between atoms of material generates current) •  Chemical (stored as chemical; bond break down of glucose by reac6ng with oxygen releases energy) •  Electrochemical (both chemical and electrical energy are stored in ba_ery) •  Nuclear (energy created by disintegra6on of unstable atoms) •  Solar (moves as electrical and magne6c energy) First Law of Thermodynamics ΔE = q + w Euniverse = Esystem + Esurroundings ΔEsystem =  ­ΔEsurroundings ΔEsystem + ΔEsurroundings = 0 = ΔEuniverse •  Energy cannot be created not destroyed; That is total energy of universe is a constant. •  Energy can be converted from one form to another or transferred from a system to the surrounding or vice versa. Energy diagrams for the transfer of internal energy (E) between a system and its surroundings ΔE = Efinal  ­ Eini6al = Eproducts  ­ Ereactants A system transferring energy as heat only The Meaning of Enthalpy w =  ­ PΔV H = E + PV ΔH ≈ ΔE in 1. Reac6ons that do not involve gases. where H is enthalpy ΔH = ΔE + PΔV qp = ΔE + PΔV = ΔH 2. Reac6ons in which the number of moles of gas does not change. 3. Reac6ons in which the number of moles of gas does change but q is >>> PΔV. Limita6ons of the First Law of Thermodynamics ΔE = q + w Euniverse = Esystem + Esurroundings ΔEsystem =  ­ΔEsurroundings ΔEsystem + ΔEsurroundings = 0 = ΔEuniverse The total energy of the universe is constant. However, this does not tell us anything about the direc6on of change in the universe. Spontaneous Processes evacuated •  Spontaneous processes proceed without any outside interven6on. •  The gas in red vessel will spontaneously effuse into blue vessel, but once the gas is in both vessels, it will not spontaneously reversed. Iron Rus6ng Spontaneous in one direc6on but nonspontaneous in the reverse direc6on. Spontaneous processes could be temperature dependent: •  Above 0°C mel6ng of ice is a spontaneous process. •  Below 0°C forma6on of ice is a spontaneous process. Enthalpy and Spontaneity Many exothermic processes ( ­ΔH) are spontaneous. All mel6ng and vaporizing processes are endothermic; these processes are also spontaneous. Therefore, the sign of enthalpy change does not indicate if a process is spontaneous or not. Why Are Some Processes Spontaneous? How to Predict Spontaneity of a Process? Thermodynamics: Entropy, Free Energy, and the Direc6on of Chemical Reac6ons 20.1 The Second Law of Thermodynamics: Spontaneous Change Predic6ng 20.2 Calcula6ng the Change in Entropy of a Reac6on 20.3 Entropy, Free Energy, and Work 20.4 Free Energy, Equilibrium, and Reac6on Direc6on ENTROPY "Energy spontaneously disperses from being localized to becoming spread out if it is not hindered from doing so.” A rock falling A hot frying pan cooling down Iron rus6ng Air leaving a punctured 6re Ice mel6ng in a warm room Dispersing Energy is internal energy, Which is molecular “mo6onal energy”: the transla6onal, vibra6onal, and rota6onal energy of molecules. ...
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