Thus the freezing of water is accompanied by a flow of heat (the heat of fusion) into the surroundings, causing Δ S surr to increase. The only way the entropy of the surroundings can be affected is by exchange of heat with the system: Δ S total = Δ S system + Δ S surroundings (3-1)
#What is the second law of thermodynamics plus#
but its the entropy of the system plus surroundings that counts! It is important to understand that the criterion for spontaneous change is the entropy change of the system and the surroundings- that is, of the world, which we denote by Δ S total: At first sight, this might seem to be inconsistent with our observations of very common instances in which there is a clear decrease in entropy, such as the freezing of a liquid, the formation of a precipitate, or the growth of an organism. In other words, all spontaneous change leads to an increase in the entropy of the world.
#What is the second law of thermodynamics free#
In any spontaneous macroscopic change, the entropy of the world increasesĪll natural processes that allow the free exchange of thermal energy amongst chemically-significant numbers of particles are accompanied by a spreading or dilution of energy that leaves the world forever changed. In the third case, the thermal energy gets concentrated into a smaller volume as the gas contracts. In the first two examples, thermal energy (dispersed) gets concentrated into organized kinetic energy of a macroscopic object- a book, a propellor. What do all these scenarios that conform to the First Law but are neverthless never seen to occur have in common? In every case, energy becomes less spread out, less "diluted". (To the extent that air behaves as a perfect gas, this doesn't involve the First Law at all.) Because motion of the air molecules is completely random, there is no reason why all of the molecules in one half of a room cannot suddenly "decide" to move into the other half, asphyxiating the unfortunate occupants of that side.As long as the work done to turn the propellor is no greater than the heat required to melt the ice, the First Law is satisfied. One might propose a scheme to propel a ship by means of a machine that takes in seawater, extracts part of its thermal energy which is used to rotate the propellor, and then tosses the resulting ice cubes overboard.Similarly, why can't the energy imparted to the nail (and to the wood) by a hammer not pop the nail back out? According to the First Law, there is no reason why placing pre-warmed book on a warmed table top should not be able to propel the book back into the air. The kinetic energy contained in the falling book is dispersed as thermal energy, slightly warming the book and the table top. Suppose you drop a book onto a table top.For simple mechanical operations on macroscopic objects, the First Law, conservation of energy, is all we usually need to determine such things as how many joules of energy is required to lift a weight or to boil some water, how many grams of glucose you must metabolize in order to climb a hill, or how much fuel your car needs to drive a given distance.īut if you think about it, there are a number of "simple mechanical operations" that never occur, even though they would not violate energy conservation.
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