Is entropy 'S' measured on some fixed scale?

[jackson6612]

I'm not a science student. Therefore, please keep your replies as simple and straightforward as possible so that your help can be fully appreciated. Thanks.

Is entropy 'S' measured on some fixed scale? If yes, then what's the maximum value?

When oxygen and hydrogen react to form water, the overall entropy decreases at the expense system losing energy and setting at lower energy state (exothermic reaction). Could you please give me an example where entropy increases and the system settles at somewhat higher energy state?

Please help me. Thanks.

 

[Mapes]

Is entropy 'S' measured on some fixed scale? If yes, then what's the maximum value?

Entropy is measured on a fixed scale, but I don't see why that would imply that there's a maximum value.

Could you please give me an example where entropy increases and the system settles at somewhat higher energy state?

This occurs in evaporation.

 

[jackson6612]

Entropy is measured on a fixed scale, but I don't see why that would imply that there's a maximum value.

Thanks a lot, Mapes. I have read Moh's, I think it's for hardness measurement, has fixed upper and lower values.

 

[Redbelly98]

Temperature is also measured on a fixed scale, but has no maximum.

 

[jackson6612]

Hi Red

Thanks. You are correct. Temperature has only minimum value, no maximum. I think on Moh's scale diamond is given the maximum hardness. Don't remember about the object given the least hardness value - perhaps, it's graphite.

 

[caracole]

Just out of curiosity, is it not true that there is a maximum amount of entropy that you could have in a given space? Like in black holes or something?

 

[espen180]

The black hole entropy is given by

$$S_{BH}=\frac{A}{4}$$ expressed in units of Planck area.

if we assume that entropy is distributed evenly throughout the hole (it may not be).

Since $$A \propto V^{\frac{2}{3}}$$, there is no upper bound on the black hole entropy density.

 

[dav2008]

Hi Red

Thanks. You are correct. Temperature has only minimum value, no maximum. I think on Moh's scale diamond is given the maximum hardness. Don't remember about the object given the least hardness value - perhaps, it's graphite.

That's just the definition of the scale. Diamond is set to 10 and talc is set to 1. That doesn't mean there aren't materials softer than talc or harder than diamond. (Although there's a limit to the hardness of a material from both a discovery and theoretical material science point of view)

 

[jackson6612]

That's just the definition of the scale. Diamond is set to 10 and talc is set to 1. That doesn't mean there aren't materials softer than talc or harder than diamond. (Although there's a limit to the hardness of a material from both a discovery and theoretical material science point of view)

Thanks, Dav.

If there is a material twice harder than diamond, then how would you rate its hardness on Moh's scale? Please guide me. Thank you.

 

[Mapes]

Thanks, Dav.

If there is a material twice harder than diamond, then how would you rate its hardness on Moh's scale? Please guide me. Thank you.

You wouldn't. The Mohs scale is just an arbitrary ranking, not a true scale with well-defined spacing. You could give your material a Mohs value of 11, if you wanted.

 

[dav2008]

Thanks, Dav.

If there is a material twice harder than diamond, then how would you rate its hardness on Moh's scale? Please guide me. Thank you.

It's purely a comparative scale (an "ordinal" scale) where certain baseline minerals were given hardness values from 1 to 10. Then you could compare any given material to these and if it was harder than a 7, but softer than an 8 you could say it's a 7.5. If something is harder than diamond you would just say it's >10 on the Moh's scale. The hardness increase between each step on the scale is not constant so you can't really say "if something is twice as hard as 10 it should have this hardness" http://en.wikipedia.org/wiki/Mohs_scale

There are other scales of hardness that are more useful and are based on an indentation measurement. Basically you have a standard indenter that's pushed into a specimen at a standard load, and a hardness value is determined from the size of the resulting indentation.

In any case, you shouldn't compare hardness to entropy since the two properties are completely different. Hardness depends on how you make the measurement and it's not really a true property of a material.

Entropy, however, is well-defined for a particular system. Looking from a statistical mechanics point of view, entropy involves nothing more than counting the possible states of a system. There is no subjectivity in counting the states. You count them and then an equation relates that number to the entropy of the system.

As you said, there is a lower bound to entropy and that is 0. However, you can imagine that in any system with entropy S you can always do something to the system to increase the entropy.

There are theories that say that the universe as a whole can potentially reach a maximum amount of entropy, but I don't know anything about these or how likely they are: http://en.wikipedia.org/wiki/Heat_death_of_the_universe

 

[jackson6612]

Dav, thank you very much. You've done a good job. By the way, I rarely refer to Wiki articles because they're are possibly written for science persons, not for a layman like me. Or, it is just that I'm a qualified stupid.