can someone pleassee help?!...on physics! =(?

Question

hey, can u please help me on some physics!!....i mean, its only basic, says the teachers, but i dont seem to understand the concept!

There are two questions:
1] Why are there no 'ideal' system in existence?
2] Which has greater internal energy-liquid alcohol at 78 degrees C or gaseous alcohol at 78 degrees C? explain.
( is it gaseous, because the particles are far apart?)

Answer 1

The first question is not a basic question. It is not even a good question. "Ideal" is what you decide to call your model. It is your definition and you may use it as you see fit. I doubt your teacher wants that particular answer to the first question, but it is a true one.

You have the right idea for the second one, but you could describe it better. First, you must heat alcohol up to turn it into a gas, so you know that the gas has more internal energy... because you added some to make it gaseous. The reason that gas molecules tend to be spaced farther apart from each other than liquids is that increased energy causes atomic motion to increase. The atoms jiggle more and more until they jiggle away into a gaseous state, so, really, the molecules are farther apart because of an increased energy, not the other way around.

Answer 2

Sounds maybe more like chemistry.
In an ideal gas, the atoms (or molecules) are theoretically like a bunch or marbles bouncing off the walls and off each other. In reality they are a bunch of marshmellows and kind of stick to each other sometimes or don't bounce very well if they hit on a face instead of a corner. Real atoms are not perfect spheres that bounce perfectly, but that's a close enough description to get some idea of what's happening at a microscopic level.
As for #2, you're correct, the gaseous has greater internal energy, but the explanation is more than particles (alcohol molecules) being farther apart. Energy must be added to a 78 degree liquid in order to get a 78 degree gas. I think this is called the energy of vaporization. This added energy is part of the new internal energy of the system when it becomes a gas. That's why alcohol on your skin will feel cold, because it sucks out energy (heat) as it evaporates.
(plenty of nerds like me still awake)

Answer 3

Simple

1. Ideal does not exist because we rely on models to make our calculations, but these are just our best models, were not sure if they are real. Also, many physical proces depend on randomness which we cannot calculate.

2. This question is ambigous since, you dont explain if the alcohol is confined in a chameber or not.

-->Remember the tripple point of gas, liquid, solid.

If they ar confined in a chamber then the liquid alcohol must have a greater internal preasure than the gaseous alcohol, Therefore, the liquid will have greater internal energy. However, if they are in a vacume than the opposite would be true.

Answer 4

1)
By definition, there are no forces acting between the molecules of an ideal gas, either attractive or repulsive. And the molecules are all points, with zero size.

Obviously, no real gas can be "ideal".

2)
The internal energy of the gaseous state is higher. It needs heat to change from liquid to gaseous state! This heat is stored as internal energy.