What is entropy?

Question

Never had a very good explanation of this, despite studyting thermodynamics at degree level, so please someone put me in the picure!

Answer 1

The entropy of a system is a measure for the amount of "chaos" or randomness of the system. It is used in the Second Law of Thermodynamics, which states that spontaneous processes always involve an increase in entropy, never a decrease.

This explain why coffee and milk mix spontaneously when you combine them, but never spontaneously separate, etc.

From a statistical point of view, the law of entropy is explained by the fact that the chaotic situations are much, much more likely than the less chaotic ones. The fundamental relationship is that

[1] ... S ~ -ln P

where S is the entropy and P the probability of a situation.

Answer 2

I personally think that entropy is an interaction between matter and energy on the one hand and empty space on the other. It is said to be a measure of randomness, but I think it is more than that. I think the best way to envision entropy is to imagine an open wide mouth jar containing about 1,000 tadpoles, and you gently sink the jar to the bottom of a pond. In not much time the tadpoles will be all over the pond, which is an increase in entropy. The tadpoles are the same and the pond is the same except for the distribution of tadpoles. If this principle did not exist, then airconditioners would not work. Entropy drives the drop in temperature of the freon, otherwise it simply would not get any cooler. Furthermore, the sun could not exist without entropy, since it would never form into a nice tidy sphere unless it was able to continuously dump huge amounts of light and heat into the empty void of space. The heat would consequently build up inside and the sun would re-expand into a nebula to the point that it got so big and rarefied that the fusion would shut off, never to re-start. Furthermore, hydrogen fusion would come to a standstill if it weren't for the fact that huge numbers of solar neutrinos are lost to empty space every second. It is the loss of nutrinos that drives the equation in the direction of Helium and away from Hydrogen. The human body has evolved to take advantage of entropy in the form of sweat glands, since sweat evaporating from your skin would not cool you without the rise in entropy that drives the evaporation. Entropy is a real part of the natural world and the universe just would not be the same without it. I hope this helps.

Answer 3

Entropy is themeasure of disorder present ina system. A system in a highly ordred state will have low entropy and a system ina disordered state will have high entropy.
If molecules in a gas are in same direction,they are in ordered state and has low entropy.Here the orderly motion of molecules can be completely converted intowork of driving the piston. If molecules move in all drections some of them will not participate in moving the piston,hence there is loss of work.This is the reason why heat energy cannot be completely converted into work.
When a system absorbs heat energy, a part is used to increase internal energy, apart to do work and other to increase the entropy.
Hence entropy is the measure of amount of energy in asystem that cannot be used to do work.
Entopy can also be used to define 2nd law of thermodynamics "The entropy of the universe is increasing".
Entropy denoted by "S". Change in entropy=Delta S
Entropy is a state function and is an extensive property.
Delta S = q/T Cal/Kelvin or Joules/Kelvin or e.u.

Answer 4

Literally it is the change in heat with respect to temperature, or dQ/T. More colloquially, it is the "disorder" in the universe (the universe is the system and its surroundings.)

The classic example used to explain entropy is a cup of ice water (the system) in a room with temperature 298K (the surroundings.) In this example, heat energy from the room will move into the cup, which can be notated as dQ. As long as there is ice in the cup, the temperature of the system is 273 kelvin. Thus, the change in entropy of the reaction that melts the ice is dQ/273K.

It is also important to know that entropy of the universe is always increasing. In the ice melting example, the entropy of the system went up by dQ/273K, whereas the entropy of the room only went down by dQ/298K.

Answer 5

entropy is a measure of the potential amount of disorder within a system. eg there are many combinations of gas molecules in a given volume, it is extremely unlikely that the molecules in tour room will all be lined up against one wall as there are very few ways of doing this but when spread throughout the room they can take many different combinations. Consider a bottle with one end evacuated, and they other filled with gas. open the seal and the gas rushes through, as the same amount of gas has a larger volume in which to organise itself there are many more combinations and hense the entropy of the system has increases

Answer 6

Entropy states that the universe as a whole tends toward a state of disorder. In other words, no process is 100% efficient and useful forms of energy such as mechanical and electrical are converted into thermal, which is not as useful. Order can increase in one area, such as a refrigerator removing thermal energy, but entropy must increase someplace else.

Answer 7

Entropy is the degree of disorder of a system. As Entropy always increases the overall disorder of a system will always tend to increase.

Answer 8

Entropy is a measure of the disorder of a system. Generally the entropy of a system with certain macroscopic characteristics (temperature, pressure, composition...) is proportional to

ln ( # microscopic states with those macroscopic characteristics )

Answer 9

I think this summarises entropy: "The world tends towards chaos."

As a sideline, I came across this while studying this topic before, which is quite similar (but not exactly), and it has ever since got stuck in my mind: Murphy's law which states that whatever can go wrong will go wrong... Something to chew on?

Answer 10

Man.. I'm with you. I have a BS in mechanical engr and I never really understood "S". I know it makes a T-S chart work. Somebody told me it measured chaos in a system.. Huh??

Enthalpy.. now that's something you can sink your teeth into.