S = 0

[Drew Myers 4G]

When does entropy equal zero?

[JonathanS 1H]

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]

Entropy is 0 in an isothermal reversible system.

[rabiasumar2E]

It's zero in an isothermal reversible reaction.

[Jessica Katzman 4F]

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

[Shivam Rana 1D]

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

[Nick Lewis 4F]

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]

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]

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

[Nathan Rothschild_2D]

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.

[Ivan Tadeja 1G]

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]

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]

its zero for an isothermal reversible reaction!

[Renee Grange 1I]

Entropy = 0 in an isothermal reversible system

[Sanjana K - 2F]

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]

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]

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]

It's zero in an isothermal reversible reaction.

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

[Anuradha S 1F]

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]

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]

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

[Sophia Spungin 2E]

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.