Are the definitions of reversible processes in thermodynamics listed below equivalent?Why?
538671
Since entropy has a rather simple (statistical) definition, I would start with that and then define a reversible process as one which does not change the entropy (of an isolated system).\n\nBut if starting with definition 2, yes it would be best to make it clear that it applies to any pair of intermediate states even though it does follow logically (because the only way it's possible to recover the initial state with no net change in the environment is when the initial and final states have the same entropy. Since entropy is nondecreasing, the entire process must be isoentropic).\n\nThe relation between definitions (1) and (2) is this: If a system is arbitrarily close to equilibrium at all points in a process (definition 1) it takes only arbitrarily tiny nudges to cause it to move in any direction and that is the sense in which it's reversible by definition (2). That is, it takes an arbitrarily small external manipulation to move it in either direction - just as a static mechanical system can be moved in either direction along a path of constant potential energy with no resistance.\n\nGenerally an irreversible process occurs when a system is allowed to move spontaneously in a direction that it "wants" to move (in a direction of increasing entropy). Simple example: allowing heat to flow directly from a hot object to a colder object in contact with it.
20347
He invented a cycle, which is externally and internally reversible, and gives the highest efficiency that any thermal machine will give between a given range of temperatures.\n\nThis cycle, however, can not be taken to practical applications, for all the four processes in the cycle involve irreversibilities that cannot be eliminated in reality.
1123465
Na2S + 2 HCl > H2S + 2 NaCl  \n\nH2SO4 + BaOH > H20 + BaSO4  \n\nNH4Cl + NaOH > NaCl + NH4OH\n\nAgNO3 + NaCl > AgCl + NaNO3\n\nnot sure about complete or reversible..:)
883295
Evaporation- liquid changes to a gas\nCondensation- gas changes to a liquid
1150533
First Law of Thermodynamics: Energy can be changed from one form to another, but it cannot be created or destroyed. \n\n"You can't win."  Because you can never get more energy than you start with.\n\nThe Second Law of Thermodynamics states that "in all energy exchanges, if no energy enters or leaves the system, the potential energy of the state will always be less than that of the initial state." \n\n"You can't break even."  Because you lose potential energy.  It changes to heat.
674447
The second law of thermodynamics states that "the entropy of an isolated system not at thermal equilibrium will tend to increase over time, approaching a maximum value."\n\nThe Second Law is a statistical law and thus applicable only to macroscopic systems. When one part of an isolated system interacts with another part, energy tends to distribute equally among the accessible energy states of the system. As a result, the system tends to approach thermal equilibrium, at which point the entropy is at a maximum and the free energy is zero.
96040
The phrasing is wierd, shouldn't there be a from between flow and the?\n\nIf two substances have different _temperatures_, heat will flow [from] the hotter [substance] to the colder [substance].\n\nThis is because heat, at the molecular level, is related to how fast molecules are moving. When a substance whose molecules are moving faster comes in contact with an object that's moving slower, the faster molecules will collide with the slower molecules of the second object, slowing down the faster molecules while speeding up the slower ones. Thus, heat (average kinetic energy of a substance) is transferred from the hotter substance to the colder one.
276230
in an ideal turbine the process is entirley reversible, meaning there is no entropy change during the process.  a real turbine involves friction and therefore entropy changes
390030
heat mainly - the energy is wasted in the form of heat instead of transferable energy
226939
First Law of Thermodynamics: Energy can be changed from one form to another, but it cannot be created or destroyed. The total amount of energy and matter in the Universe remains constant, merely changing from one form to another. The First Law of Thermodynamics (Conservation) states that energy is always conserved, it cannot be created or destroyed. In essence, energy can be converted from one form into another.\nWhen electrical fan is rotating, electrical energy is transformed to mechanical energy.\nEntropy and the Second Law of Thermodynamics\nThe second law of thermodynamics (the entropy law or law of entropy) was formulated in the middle of the last century by Clausius and Thomson following Carnot's earlier observation that, like the fall or flow of a stream that turns a mill wheel, it is the "fall" or flow of heat from higher to lower temperatures that motivates a steam engine. The key insight was that the world is inherently active, and that whenever an energy distribution is out of equilibrium a potential or thermodynamic "force" (the gradient of a potential) exists that the world acts spontaneously to dissipate or minimize. All real-world change or dynamics is seen to follow, or be motivated, by this law. So whereas the first law expresses that which remains the same, or is time-symmetric, in all real-world processes the second law expresses that which changes and motivates the change, the fundamental time-asymmetry, in all real-world process. Clausius coined the term "entropy" to refer to the dissipated potential and the second law, in its most general form, states that the world acts spontaneously to minimize potentials (or equivalently maximize entropy), and with this, active end-directedness or time-asymmetry was, for the first time, given a universal physical basis. The balance equation of the second law, expressed as S > 0, says that in all natural processes the entropy of the world always increases, and thus whereas with the first law there is no time, and the past, present, and future are indistinguishable, the second law, with its one-way flow, introduces the basis for telling the difference. \nThe active nature of the second law is intuitively easy to grasp and empirically demonstrate. If a glass of hot liquid, for example, is placed in a colder room a potential exists and a flow of heat is spontaneously produced from the cup to the room until it is minimized (or the entropy is maximized) at which point the temperatures are the same and all flows stop.\nThird Law of Thermodynamics\n\nThe third law of thermodynamics states that if all the thermal motion of molecules (kinetic energy) could be removed, a state called absolute zero would occur. Absolute zero results in a temperature of 0 Kelvins or -273.15° Celsius.\n\nAbsolute Zero = 0 Kelvins = -273.15° Celsius\nThe Universe will attain absolute zero when all energy and matter is randomly distributed across space. The current temperature of empty space in the Universe is about 2.7 Kelvins.\nAt the absolute zero of temperature, there is zero thermal energy or heat. Since heat is a measure of average molecular motion, zero thermal energy means that the average atom does not move at all. Since no atom can have less than zero motion, the motion of every individual atom must be zero when the average molecular motion is zero. When none of the atoms which make up a perfectly ordered crystal move at all, there can be no disorder or different states possible for the crystal
744754
In a reversible reaction, the products can be the reactants and the reactants can be the products and the whole thing goes the other way around, sort of like an 'undo'. Many reactions are at least partly reversible, and they establish an equilibrium where nothing seems to be happening because at the same time one is going the opposite is. A nonreversible reaction only goes one way or goes in one way to such a high percent it is virtually nonreversible.
1177708
Please expand on which type of "equivalents" you mean as in substitutes or normality equivalents.  For suppliers, go here:\n\nhttp://www.chemcyc.com/ME2/Default.asp
1000410
2nd Law of Thermodynamics....the irreversible trend toward equilibrium and total disorder.....its the law of the universe and nature.
271632
A heat engine typically uses energy provided in the form of heat to do work and then exhausts the heat which cannot be used to do work. Thermodynamics is the study of the relationships between heat and work. The first law and second law of thermodynamics constrain the operation of a heat engine. The first law is the application of conservation of energy to the system, and the second sets limits on the possible efficiency of the machine and determines the direction of energy flow. \nHeat engines are typically illustrated on a PV diagram  Heat engines such as automobile engines operate in a cyclic manner, adding energy in the form of heat in one part of the cycle and using that energy to do useful work in another part of the cycle.
409423
You have to specify the energy migration profile. Either adiabatic (zero energy transfer) or iso-volumetric (a lot of energy entering the system) or something in between.\n\nAlso, you have to specify the thermal units (Celsius/Fahrenheit/Kelvin/Rankin).
432767
The most fundamental equation to both areas is:\n\nAccumulation = Inputs - Outputs + Generation - Consumption\n\nMost everything else builds on that basic equation.  The thing is, there are entire textbooks for mass transfer and thermodynamics.  Similarly, different fields of engineering use different specialized forms of the equations.  I would suggest reading some textbooks.  If you have a more specific question, ask it, but for such a broad question, you need to refer to the text books and read.\n\nAs a chemical engineer, I would suggest:\n\nThermodynamics:\nJ Richard Elliott and Lira's Intro to Thermo book\n\nMass Transfer:\nBird, Stewart, and Lightfoot Transport Phenomena (THE Bible of fluid flow)\nMcCabe, Smith, and Harriet Mass Transfer Operations (more about unit operations... distillation, pumping, etc)
799142
Hi Kitty,\nHere is what, I think, you need.\n\nExothermic, dH < 0, Entropy increases (dS > 0), Reaction is spontaneous and dG < 0\n\nExothermic, dH < 0, Entropy decreases (dS < 0), Reaction is spontaneous only at low temps, if |T dS| < |dH|\n\nEndothermic, dH > 0, Entropy increases (dS > 0), Reaction is spontaneous only  at high temps, if T dS > dH\n\nEndothermic, dH > 0, Entropy decreases (dS < 0), Reaction is not spontaneous, dG > 0