## S = 0

Volume: $\Delta S = nR\ln \frac{V_{2}}{V_{1}}$
Temperature: $\Delta S = nC\ln \frac{T_{2}}{T_{1}}$

Drew Myers 4G
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### S = 0

When does entropy equal zero?

JonathanS 1H
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### Re: S = 0

Entropy total is equal to 0 when there is a reversible reaction since the reaction is 'at equilibrium' throughout the whole time. Entropy of the surroundings is equal to 0 with an expansion against a vaccum.

805383532
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### Re: S = 0

Entropy is 0 in an isothermal reversible system.

rabiasumar2E
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### Re: S = 0

It's zero in an isothermal reversible reaction.

Jessica Katzman 4F
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### Re: S = 0

When your system is isothermal and your reaction is reversible, s = 0 because the reaction is considered at equilibrium throughout.

Shivam Rana 1D
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### Re: S = 0

Entropy can also equal zero at absolute zero when the molecules only have one orientable state (no residual entropy).

Nick Lewis 4F
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### Re: S = 0

Entropy is considered 0 in an isothermal reversible expansion reaction because entropy is a state function and ends in the same final state that it initially starts in.

Shutong Hou_1F
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### Re: S = 0

S just means entropy, rather than change in entropy that should be denoted as ΔS. Entropy is almost never 0 (the entropies of all perfect crystals approach zero as the absolute temperature approaches zero; "perfect crystal" refers to a substance in which all the atoms are in a perfectly orderly array.), because even at absolute 0 where all molecular motion has ceased, positional (residual) entropy, present because of different microstates, still exists.

VioletKo3F
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### Re: S = 0

S, or entropy, is zero in an isothermal reversible system since it it always at equilibrium.

Nathan Rothschild_2D
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### Re: S = 0

An example would be a perfect crystal like diamond at absolute zero. However absolute zero is impossible to reach at the moment and can only be reached theoretically.

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### Re: S = 0

Shutong Hou_1F wrote:S just means entropy, rather than change in entropy that should be denoted as ΔS. Entropy is almost never 0 (the entropies of all perfect crystals approach zero as the absolute temperature approaches zero; "perfect crystal" refers to a substance in which all the atoms are in a perfectly orderly array.), because even at absolute 0 where all molecular motion has ceased, positional (residual) entropy, present because of different microstates, still exists.

What would be the meaning/differences of positive/negative entropies?

Rhea Shah 2F
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### Re: S = 0

In an isothermal reaction, the change in surrounding entropy is zero because energy is not transferred to the surroundings. In a reversible reaction, the total entropy change is equal to zero because the system is in equilibrium.

Sreyes_1C
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### Re: S = 0

its zero for an isothermal reversible reaction!

Renee Grange 1I
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### Re: S = 0

Entropy = 0 in an isothermal reversible system

Sanjana K - 2F
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### Re: S = 0

Shutong Hou_1F wrote:S just means entropy, rather than change in entropy that should be denoted as ΔS. Entropy is almost never 0 (the entropies of all perfect crystals approach zero as the absolute temperature approaches zero; "perfect crystal" refers to a substance in which all the atoms are in a perfectly orderly array.), because even at absolute 0 where all molecular motion has ceased, positional (residual) entropy, present because of different microstates, still exists.

What would be the meaning/differences of positive/negative entropies?

Entropy > 0 means the reaction is favoring an increase in disorder and entropy < 0 means it's favoring order (or less disorder).

Philip
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### Re: S = 0

The total change in entropy is 0 if the system is isothermal and reversible expansion. The entropy change of the surrounding is 0 if the system is isothermal and irreversible expansion.

William Chan 1D
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### Re: S = 0

Having zero entropy is theoretical. The substance must be in a perfect crystal structure at absolute zero. This would eliminate any positional entropy as well as any entropy from movement.

Mariah
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### Re: S = 0

rabiasumar2E wrote:It's zero in an isothermal reversible reaction.

Can you explain how we know whether or not it is isothermal?

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### Re: S = 0

Mariah wrote:
rabiasumar2E wrote:It's zero in an isothermal reversible reaction.

Can you explain how we know whether or not it is isothermal?

The problem usually say whether or not a reaction is isothermal

AJForte-2C
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### Re: S = 0

Having S=0 will never occur in reality. Theoretically it would occur in an object/system that it is at absolute 0, and is in a perfect crystal. This would mean that it would have no residual entropy.

Sean Wang 1F
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### Re: S = 0

S will equal 0 when the system is an isothermal reversible reaction.

Sophia Spungin 2E
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### Re: S = 0

I believe entropy=0 when there is only 1 structural configuration. For example, O2 gas only has 1 structural configuration and therefor has an entropy of 0.