Constant temperature change in a system

Question

Constant temperature change in a system

Ozone (Chemical)

(OP)

14 May 03 05:04

Hi,
i had always believed that when heat is transfered from surrounding to a system, temperature must respond within the system (an increase in this case). but recently i came across an example in a text where heat was added to a system and temperature remained constant. could it be that i have had a wrong notion all this while?

quark (Mechanical) · Answer 1 · 2003-05-14 05:13:20

Yes. Your notion was wrong. For example consider melting of Ice or boiling of water.

In both cases, you should supply latent heat to change the phases but temperature remains constant.

Ozone (Chemical) · Answer 2 · 2003-05-14 06:04:22

I am aware of latent heat, i forget to state that the heat added was not latent. Visible heat tranfer to a gas that is what i am talking about here.

25362 (Chemical) · Answer 3 · 2003-05-14 07:06:15

An ideal gas (pV = nRT) can be expanded reversibly and isothermally by the absorption of heat. Since the internal energy of an ideal gas cannot change in an isothermal process, dU= 0 = dQ + dW. For a mechanical reversible non-flow process Q = -W = RTln(V₂/V₁), since P₁/P₂ = V₂/V₁, one can also write Q = -W = RT ln(P₁/P₂).

hacksaw (Mechanical) · Answer 4 · 2003-05-14 09:16:49

visible heat that is a new one. unless you are alluding to real gas supercritical behavior, 25362 comments are right on.

Ozone (Chemical) · Answer 5 · 2003-05-15 03:30:55

thanks to all who contributed to clarify me. Especially 25362 and to HACKSAW , i actually meant sensible heat thanks for the observation. hoping we could share knowledge the more in this forum.

hacksaw (Mechanical) · Answer 6 · 2003-05-15 09:37:07

any ideas on how estimate the specific of molten iron at 1000 m hydrostatic head?

phex (Chemical) · Answer 7 · 2003-05-15 09:48:06

i'd like to help, but what 'specific' are u looking for?

;)

quark (Mechanical) · Answer 8 · 2003-05-16 00:00:27

First of all I am very sorry to trivialize the original post and I agree that I should have a little bit high estimation.

25362 is correct asusual. But that is possible (and is evident from his equation) if and only if work is done by the system external to it.

Once again I am sorry.

Ozone (Chemical) · Answer 9 · 2003-05-19 09:27:05

to hacksaw, ur question is not clear. specific what of iron?
to quark: u are really a nice guy. u need not apologise, i completely understand.

hacksaw (Mechanical) · Answer 10 · 2003-05-19 09:49:20

the constant pressure and constant volume specific heat

phex (Chemical) · Answer 11 · 2003-05-19 10:04:39

to hacksaw:

perhaps this is of some worth for you.

http://www.moderncasting.com/archive/WebOnly/0802/02_146.pdf

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Constant temperature change in a system