[cvc121]

Hi,

I am having a little bit of trouble relating equilibrium to some real life situations.

Ex. Which of the following are equilibrium situations. Briefly explain.

a) During a football game, 22 players are on the field and the rest are on the bench.
b) The student population at a school is constant over a period of 5 years.
c) The mercury vapour in a thermometer when the temperature is constant.
d) A glass of iced tea, which has undissolved sugar at the bottom after being stirred for half an hour (there is no ice remaining).
e) During school hours, 15% of the students are in gym class (disregard before and after school hours).
f) A well-fed lion in its cage. The lion's weight is constant.

Here are my attempts:

a) Yes; although there are substitutions, there are always 22 players on the field at a time and the rest on the bench so there are no observable changes.
b) No; although the same number of people are coming and leaving each year, it is not a closed system.
c) Yes; a thermometer is a closed system and there are no observable changes since temperature is kept constant.
d) Not sure about this one...
e) Yes; no observable changes throughout the school day.
f) Really confused about this one...

Any clarifications would be greatly appreciated. Thanks!

[Corribus]

I agree with most of your answers. These things aren't cut and dry, though. Applying simple chemical equilibrium concepts to complex systems can be difficult and not always useful. For (d).. it is a closed system? This would be an easy way to get at a potential answer for that one. The salt may be in equilibrium with the water, but is there anything else about the system that may not be?

For (e)  what does it mean to say the lion's weight is constant? It won't be, if you don't continue to feed it. But until the source of energy is removed, the system won't exhibit any significant macroscale changes. (Within reason, of course. Eventually the system will gradually change, because the lion will age. So, I think you could probably make a reasonable argument either way.)