## 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
Posts: 100
Joined: Sat Aug 17, 2019 12:17 am

### S = 0

When does entropy equal zero?

JonathanS 1H
Posts: 101
Joined: Thu Jul 11, 2019 12:17 am

### 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
Posts: 53
Joined: Thu Jul 11, 2019 12:16 am

### Re: S = 0

Entropy is 0 in an isothermal reversible system.

rabiasumar2E
Posts: 108
Joined: Thu Jul 11, 2019 12:15 am

### Re: S = 0

It's zero in an isothermal reversible reaction.

Jessica Katzman 4F
Posts: 35
Joined: Mon Jun 17, 2019 7:24 am

### 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
Posts: 106
Joined: Fri Aug 09, 2019 12:16 am

### 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
Posts: 111
Joined: Wed Sep 18, 2019 12:18 am

### 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
Posts: 117
Joined: Sat Sep 14, 2019 12:17 am

### 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
Posts: 103
Joined: Sat Sep 07, 2019 12:18 am

### Re: S = 0

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

Nathan Rothschild_2D
Posts: 131
Joined: Fri Aug 02, 2019 12:15 am

### 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.

Posts: 81
Joined: Fri Sep 28, 2018 12:28 am

### 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
Posts: 97
Joined: Thu Jul 25, 2019 12:17 am

### 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
Posts: 90
Joined: Fri Sep 28, 2018 12:19 am

### Re: S = 0

its zero for an isothermal reversible reaction!

Renee Grange 1I
Posts: 56
Joined: Fri Aug 30, 2019 12:16 am
Been upvoted: 1 time

### Re: S = 0

Entropy = 0 in an isothermal reversible system

Sanjana K - 2F
Posts: 102
Joined: Sat Sep 07, 2019 12:17 am
Been upvoted: 1 time

### 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
Posts: 100
Joined: Sat Sep 07, 2019 12:16 am

### 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
Posts: 102
Joined: Sat Sep 14, 2019 12:15 am

### 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
Posts: 104
Joined: Fri Aug 02, 2019 12:16 am

### 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?

Posts: 50
Joined: Fri Sep 27, 2019 12:29 am

### 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