Quick Chemistry Question on Entropy?

Question by bandgeek44: Quick Chemistry Question on Entropy?
Okay, my question is for which process is delta S (entropy) negative?
a. evaporation of 1 mol of CCl4 (l)
b. mixing 5ml ethanol with 25 ml water
c. raising the temperature of 100g Cu from 275K to 295K.
d. grinding a large crystal of KCl to powder
e. compressing one mol Ne at constant temperature from 1.5 atm to .5 atm

I narrowed it down to C or E, but I’m still not completely sure…Can anyone be so kind as to help me and tell me why it is what it is? :]

Best answer:

Answer by Dragon
I suggest “e” is the answer since it increases order / organization.

“a”, “b”, “c”, and “d” decrease order / organization by increasing random motion and/or distance between molecules.


In many processes in modern technology, for example conversion of energy from one form to other the net availability of energy decreases. This decrease of available energy is called entropy. It is on this principle the engines worked. All such processes have efficiencies less than one. That is the net output energy is always less than input. As a rule the entropy is increasing. We are moving from organization to disorganization or from order to disorder. The second Law of Thermodynamics states that the entropy of a system tends to get higher as time progresses because disorganization increases. The law of entropy is considered to be a basic law of nature and the universe.

Negative Entropy

However living things behave in oppsite manner. All living things attempt to modify their environment for their own needs, by creating what for them is order. In 1943 Erwin Schrödinger, Nobel Lauriate in Physics, used the concept of “negative entropy” in his popular-science book What is life? A living system imports negentropy and stores it. Life feeds on negative entropy!

The creation of order is one definition of negative entropy. One of the definitions of life might be the ability of a life form to create order. Rocks or other inanimate objects do not possess this property called negative entropy. Death might be defined as the inability of a living thing to continue to create negative entropy for its use. As long as a life form exists, it creates negative entropy, which we observe as the creation of order. The creation of negative entropy is a reversal of the law of entropy.

What is the source of negative entropy? The Sun’s energy is highly organized and carried by photons. Our Biosphere absorbs this energy and then releases it back to the Universe -the global balance of energy is zero. The black body radiation of the Sun at a temperature of 5800 degrees Kelvin is absorbed by the Biosphere and the black body radiation from the Biosphere and Earth at 280 degrees Kelvin flows to the Universe, which is at a temperature of 3 degrees Kelvin.

How does life steal energy from the Sun? This is done through a process called photosynthesis. With this process the green matter in plants converts the Sun’s energy to usable energy for the plant growth. Herbivores and carnivores sustain and reproduce themselves by using the Sun’s energy through plants. This process is not available to non-living things.

Thus biological processes creating negative entropy, unlike the mechanical processes, produces more energy that they take. The efficiency is always greater than one. Typically it is about 2.5. That is for one unit of energy (calories) input say in a ‘primitive’ sustainable farm in the form of human and animal energy we get two calories of consumable energy output! How do we get more out put from less input? As we said above we are not including the input from the Sun. And this is not available to non-biological processes.

Compare this with American ‘agribusiness’, which in 1976 took 5 calories of fertilizers, tractor fuel and depreciation, human labour and chemical sprays to produce one calorie of food and an incredible extra 20 calories of energy to clean, package, transport and cook the food ready for eating in the city. Thus the primitive self-sufficient peasant life is at least 50 times more efficient than industrialised food production. The reason is that the primitive agriculture uses mainly biological or life processes, which have normally efficiencies greater than one whereas industrial processes use mainly non-biological input and processes.

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