### negative entropy

Posted:

**Sun Feb 04, 2018 12:32 pm**Does a negative entropy mean no disorder?

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=131&t=26833

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Posted: **Sun Feb 04, 2018 12:32 pm**

Does a negative entropy mean no disorder?

Posted: **Sun Feb 04, 2018 12:45 pm**

The change in entropy can be negative, and when this is the case, you can think of it as a system becoming more ordered. An example would be of condensation, in the transition from a gas (high entropy state) to a liquid (low entropy state).

Posted: **Sun Feb 04, 2018 12:48 pm**

The formula used to determine entropy, S= lnW requires that W be a positive number, since you can't have a negative number of microstates, and thus, can't have a negative degeneracy. Because of this, I don't think there is any way that you'd be able to have a system with a negative entropy.

Posted: **Sun Feb 04, 2018 4:56 pm**

There is no such thing as negative entropy, but a negative change in entropy exists. For example, a reaction that condenses from a gas to liquid would have a negative delta S because the liquid would occupy less possible states than the gas due to the decrease in temperature and volume.

Posted: **Sun Feb 04, 2018 7:40 pm**

Entropy must practically always be positive, since S approaches 0 as T approaches 0. The third law of thermodynamics holds that "The entropies of all perfect crystals approach zero as the absolute temperature approaches zero."

Posted: **Mon Feb 05, 2018 12:44 am**

A negative entropy just means that the system is becoming more ordered, it doesn't mean that there isn't any entropy.

Posted: **Mon Feb 05, 2018 9:59 am**

no, it just means the system is becoming more ordered.

Posted: **Mon Feb 05, 2018 12:11 pm**

There is no such thing as negative entropy. The negative delta entropy means a decrease in disorder.

Posted: **Mon Feb 05, 2018 12:39 pm**

Look at the signs in entropy as a change rather than positive and negative entropy.

Posted: **Mon Feb 05, 2018 2:17 pm**

Negative entropy simply means that there is a decrease in disorder, or rather an increase in order of the system.

Posted: **Mon Feb 05, 2018 2:54 pm**

I think an important delineation to make is whether or not you're referring to entropy (S) or change in entropy (ΔS).

Entropy in its absolute value is calculated by using the Boltzmann equation, S= k ln W. In terms of entropy in its absolute value (calculated through the previous equation), no, negative entropy does not exist. A system either has no disorder (which results in a 0 value for S), or some disorder (which results in a positive value for S).

But, I think your question here involves calculating change in entropy, aka the second law of Thermodynamics, ΔS= -qrev/T. In this scenario, it is perfectly acceptable for the obtained value to be negative-- as many other people in this thread have already clarified, that just indicates that the system is becoming more ordered through whatever change is taking place.

Entropy in its absolute value is calculated by using the Boltzmann equation, S= k ln W. In terms of entropy in its absolute value (calculated through the previous equation), no, negative entropy does not exist. A system either has no disorder (which results in a 0 value for S), or some disorder (which results in a positive value for S).

But, I think your question here involves calculating change in entropy, aka the second law of Thermodynamics, ΔS= -qrev/T. In this scenario, it is perfectly acceptable for the obtained value to be negative-- as many other people in this thread have already clarified, that just indicates that the system is becoming more ordered through whatever change is taking place.