ENTROPY
1.
a thermodynamic quantity representing the unavailability of a system's thermal energy for conversion into mechanical work, often interpreted as the degree of disorder or randomness in the system.
"the second law of thermodynamics says that entropy always increases with time"
2.
lack of order or predictability; gradual decline into disorder.

As I understand it, there is a constant increase of entropy in the universe, meaning that the universe grows colder and colder.
As energy gets converted from one form to another (for example heat->mechanical) there is a net energy loss and entropy increases.
When entropy is 100%/maximum in a system all matter have a temperature of zero kelvin. (?)
In a closed system with maximum entropy there is no energy left (?) - What about gravitational forces? from the definition (1.) above it only states that there is no thermal energy left which I understand as all matter being at zero kelvin.

Anyways my main problem with understanding the definition of entropy comes from the conflicting ideas of 1. and 2.

When entropy is at it's highest all matter stand still (no vibration of molecules, atoms - what about electrons?), which to me means that there is a higher amount of predictability and order.
It seems to me that matter at extreme temperatures vibrating and acting more "volatile" would collerate to a higher degree of disorder and unpredictability.

I would appreciate if someone knowledable on the subject could enlighten me.

When a system is at 0K entropy is minimized, you have it backwards.

a thermodynamic quantity representing the unavailability of a system's thermal energy for conversion into mechanical work - The way I read this statement, it is the opposite? It says here entropy is used to quantify the UNavailability of a system's thermal energy?
This is the part that really has me confused about the definition and meaning of entropy in this sense (as it makes more sense to me that given the meaning of the word entropy, it should be used like you said in your quote).

Also Entropy always increases in a closed system? "the second law of thermodynamics says that entropy always increases with time"
When energy is converted from one form to another there is always a net energy loss.

The way I read your statement in comparison to the second law is that in a closed system everything will always get hotter (which is wrong).

Can you care to elaborate a bit?

This post was edited by Dragon_Reborn on Oct 14 2015 08:45am

A system doesn't need to be at 0k for it to be impossible for the system to do work. A system will naturally reach the same temperature as it's surroundings, and when that happens and energy is evenly dispersed no work can be done even though there is thermal energy in the system.

Oh I understand what you say, and I am pretty sure I understand.
Thanks for taking the time to explain, I were thinking about it the wrong way.

I just thought about what makes the earth cool down at "night" (even though there is day everwhere but you know), and that is a part of the process where entropy increases, thermal energy is being converted to work in one way or another. Through this process there is a sustained net loss of energy. Say there was no sun (or stars etc), eventually there would be no available way to convert energy even though there still is thermal energy. Everything would eventually have the same thermal energy (what about the core though? higher gravitational force and pressure = higher temperature? irrelevant?), no way to convert energy and maximum entrophy. The sun is what makes or system "not closed" and keeps entropy in balance.

Did I get it?

I still feel that a system with high entropy (same thermal energy, no energy changing forms, lifeless) seems more orderly and predictable than the other way around

This post was edited by Dragon_Reborn on Oct 14 2015 09:00am

On the macro level it is more predictable, but at the molecular level you have maximized the number of potential states for each molecule, so it's harder to predict the state of the system. Entropy is a feature that arises from the number of potential microstates. To calculate the entropy you actually use the following formula.

Kb ln(W). Where kb is the boltzman constant, ln is natural log, and W is the number of potential microstates the system can take on and express the same macro variables (temp, pressure, volume).

As for the center of the earth I'll address that.

The center of the earth is heated by heavier stuff falling down to the center. When you drop a ball and it bounces, eventually it stops bouncing and releases that bouncing energy as heat. That same process happens as heavy stuff like iron drops to the center, it releases heat which can't easily dissipate. Eventually though it will dissipate. Mars has a cold core for this reason.

https://en.wikipedia.org/wiki/Introduction_to_entropy

For an irreversible process in an isolated system, the thermodynamic state variable known as entropy is always increasing.