# Question related to Zeroth law of thermodynamics

1. Jun 5, 2012

### LEGEND_XEON

I have given enough thought to this but couldn't get anywhere.I would be glad if you express your thoughts on this.

Q:Zeroth law of thermodynamics is not valid for which one of the following,

(a) 50 ml of water at 25°C is mixed with 150 ml of water at 25°C

(b) 500 ml of milk at 15°C is mixed with 100 ml of water at 15°C

(c) 5 kg of wet steam at 100°C is mixed with 50 kg of dry and saturated steam

(d) 10 ml of water at 20°C is mixed with 10 ml of Sulfuric acid at 20°C

Last edited by a moderator: Jun 5, 2012
2. Jun 5, 2012

### Studiot

So what were your thoughts?

Can you for instance say that it is valid for any of them?
If so what is the difference.

Presumably the cases refer to mixing the said components.

Does this result in any change when you do this and does the zeroth law apply to that change?

Edit are you sure you have copied (c) correctly?

Last edited: Jun 5, 2012
3. Jun 5, 2012

### LEGEND_XEON

That's where i am confused. There is no reference to third body.
Probably it is asking for a mixture in which there is Heat Transfer.

In my case it is (d) since reaction between water and sulfuric acid is an exothermic reaction. It could be (c) also. Not sure in both the cases.

4. Jun 5, 2012

### Studiot

Due to some glitch in the system the mods combining your threads didn't alert me to your reply so I thought you hadn't.

Moral don't double post.

~As to the issue

Well the zeroth law (contracted a bit) says

Two bodies in contact are at the same temperature when in thermal equilibrium.

No third body is actually necessary.

Now if we turn that round and ask what is thermal equilibrium?

Well it means no heat flows between contacting bodies in equilibrium.

Now apply that to the four cases you have offered.

What happens in each case?

1)Is there any heat flow?
2)Does anything else happen?

You have already answered (d2)
Yes something does happen there is a chemical reaction.
So are they in equilibrium?

How about C1 and C2?

Can the wet steam get any drier or the dry steam any wetter?
Can anything else happen?
So is there any heat transfer?
So are they in equilibrium?

So which case is not in equilibrium?

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