Transitions between states of matter: It's more complicated, scientists find

Transitions between states of matter: It's more complicated, scientists find

The seemingly simple process of phase changes-those transitions between states of matter-is more complex than previously known, NYU Chemistry Professor Mark Tuckerman and his colleagues have found. Their study reveals the need to rethink one of science's building blocks and, with it, how some of the basic principles underlying the behavior of matter are taught in our classrooms.

In all this new complexity, where does the role of photons, energy levels, and escape velocity of electrons come in to play, in determining the gas or solid state of matter?   (The liquid state of matter is not, in the strictest sense of the word, a true state of matter at all because it is dependent almost entirely upon exterior influences). 

As research discovers new twists and turns of a river, why disconnect from the river?

"This research shows that phase changes can follow multiple pathways, which is counter to what we've previously known," explains Mark Tuckerman, a professor of chemistry and applied mathematics at New York University and one of the study's co-authors. "This means the simple theories about phase transitions that we teach in classes are just not right."

Back to the ‘river’, fundamental basics, and google with awe the twists and turns.

SOLIDS, LIQUIDS AND GASES

Before going farther in our study of the phenomenon which we call heat, it might be well to consider briefly, the three states of matter which result from the various degrees of heat energy or temperature which the matter may possess at a given time.

Let us consider first, a quantity, or block of atoms or molecules in which the total number of photons contained is small. The orbits of the electrons, and therefore the size of the atom is also small. The oscillation or ‘bouncing’ of each atom will continue, but the path of each bounce will be small because the atoms or molecules are quite close together, and their critical distance is small. Since none of the particles reach escape velocity, each particle will remain in the same relative position with respect to the others. The mass will retain its shape indefinitely, and a considerable amount of outside force would have to be applied to cause the body to change in shape. This condition is known as the solid state of matter.

If, to such a block of matter, we suddenly added a large quantity of energy in the form of photons, the orbits of the atoms would spring outward, the velocity of their oscillation would increase tremendously, and soon every particle would acquire a velocity greater than its escape velocity. The particles in the interior of the mass could not immediately escape because they would still be bouncing about among their neighbors, but the field of each particle would now be repelling all of its neighbors, and the mass would expand rapidly. The particles on the outside of the mass would move outward indefinitely, leaving the next layer free to escape and so on. Matter in this condition is known as ‘gas.’

Specifically, a gas is defined as being a body of matter in which all, or virtually all of its particles have velocities in excess of the escape velocity for the particular conditions in which they exist.

We can readily see that a gas, if released in a vacuum, will expand indefinitely, and if released within a solid container will expand until it is uniformly distributed throughout the volume of the container. Each atom or molecule, upon colliding with another, will glance off in a new direction, and will continue in that direction until another collision occurs.

The average, or ‘mean’ distance which a particle travels between such collisions is know as ‘the mean free path.’ In a dense, or ‘compressed’ gas the mean free path would be a very tiny fraction of an inch, but in a very rarified gas, it might be many feet.

The liquid state of matter is not, in the strictest sense of the word, a true state of matter at all because it is dependent almost entirely upon exterior influences, such as the earth’s gravitational field, its atmospheric pressure, etc. If we were to take a sample of almost any liquid to a remote point in space where there were no gravitational fields or atmosphere to affect the sample we would find that, even though we maintained the temperature at the same level, the liquid would have the characteristics either of a soft solid or of a gas.

A liquid can be defined as a body of matter whose particles have velocities either slightly below or slightly above their natural escape velocity. Most oils or liquid metals, for instance, can be described as matter whose particle velocities are so close to that of escape that the additional force applied by a gravitational field such as that of the earth is sufficient to cause the particles to escape, or ‘flow’ in the direction of the force applied by the field. If such matter were removed from the influence of exterior fields, and released in space, it would immediately assume the shape of a sphere, which shape it would retain indefinitely so long as no exterior force were brought to bear. It would, therefore have the characteristics of a very soft solid.

A glass of ordinary water, on the other hand, has the characteristics of a gas, which is prevented from expanding by the pressure of the atmosphere around it.

We can demonstrate this if we take a glass of water which is at, say 100 degrees Fahrenheit, place it in a bell jar, and suddenly remove the air from the jar. The water will immediately begin to boil quite briskly. If we maintain the temperature of the water at 100 degrees and pump out the gas as it is formed, the glass will soon be empty, demonstrating that its particles do have velocities above those necessary for escape. Actually, even though we do not remove the air, molecules of the water will constantly be escaping from the surface in spite of the downward bombardment of the air molecules, and the glass would eventually become empty. This, much slower process of escape by the mingling of the molecules of a liquid with the molecules of a surrounding gas is known as evaporation.