Give me some responses to the questions below and I'll give you some extra credit.

SID#:

Laboratory Section: 1 2 3 4 5 6

1. Before beginning the animation indicate what conditions of pressure (high, intermediate, or low) and what conditions of temperature (high, intermediate, or low) favor the solid phase? the liquid phase? and the gas phase?

Expert Response:

Conditions that favor the solid phase are low temperature and high pressure. Conditions that favor the gas phase are high temperature and low pressure. Conditions that favor the liquid phase are intermediate temperature and intermediate pressure.

2. After the phase diagram is drawn indicate the name of the phase changes that occur on the line between the solid phase and the gas phase; the liquid phase and the gas phase; the solid phase and the liquid phase.

Expert Response:

Sublimation/deposition is the phase change that occurs on the line between the solid phase and the gas phase. Evaporation/condensation is the phase change that occurs on the line between the liquid phase and the gas phase.
Freezing/melting is the phase change that occurs on the line between the solid phase and the liquid phase.

3. What is the triple point for a pue substance?

Expert Response:

The triple point is the point on the phase diagram where the three phase transition lines meet. It is defined as the pressure and temperature at which all three phases of a substance are in equilibrium.

4. What phase(s) are present at point A? What phase(s) are present at point B? What phase(s) are present at point C? What phase(s) are present at point D? What phase(s) are present at point E? (You have to be careful as the mouse click after the letter apears reveals the answer.)

Expert Response:

Point A: Solid phase

Point B: Solid and Liquid phase

Point C: Liquid phase

Point D: Liquid and Gas phase

Point E: Gas phase

5. What phase(s) are present at point F? What phase(s) are present at point G? What phase(s) are present at point H? What phase(s) are present at point I? What phase(s) are present at point J? (You have to be careful as the mouse click after the letter apears reveals the answer.)

Expert Response:

Point F: Gas phase

Point G: Solid and Gas phase

Point H: Solid phase

Point I: Solid and Liquid phase

Point J: Liquid phase

6. What is interesting about moving along the line from F to J?

Expert Response:

Moving along the line at constant temperature as the pressure increases causes the sample, initially in the gas phase, to first solidify. We might normally expect a sample to liquify as pressure increase. When a sample in the gas phase at constant temperature is compressed, the density begins to increase. For water the density of the solid is lower than the density of the liquid. So as the volume is compressed the density of the sample will continuously increase, it will reach the density of the solid before that of the liquid. So in this case the sample moves directly from the gas phase to the solid phase. Only as the pressure is increased further does the solid melt forming a liquid.

7. Is there anything about this animation that you feel you do not understand? List your concerns/questions.

What is a phase diagram? A phase diagram is a pictorial representation of the conditions of temperature and pressure for each phase of a pure substance. The phase diagram also describes the temperatures and pressure where the phases are in equilibrium. We have been discussing the three phases and we've talked about the liquid/vapor equilibrium condition as described by the Clausius-Clapyron equation. The phase diagram places this information in a context. There are other phase diagrams; P-V-T 3 dimensional phase diagrams; solution/mixtures phase diagrams; and others. The P-T phase diagram is just one example. Check out PS2.1 to see the kind of question I might ask using a phase diagram.

What is a pure substance? A pure substance is either an element or a compound. For example if we are discussing a pure substance such as sodium (an element) than the sample only contains sodium atoms, it is pure. If the substance is a compound like NaCl, sodium chloride, than the sample only contains sodium ions and chloride ions and no other atoms, molecules or ions.

What is the critical point? The critical point is the point at which no matter how high the pressure exerted on the sample we can not change the phase of the pure substance. At a temperature below the critical point we can expect that increasing the pressure can cause a phase change from liquid to vapor or visa versa. Above the critical point an increase in pressure will not change the phase. It is interesting that if we look at a sample at any point on the line separating the liquid from the gas we would expect to see a liquid and some vapor. As we approach the critical point the ability to see the different phases disappears. That is at the critical point we see only a single phase. The phase appears most like a vapor. As we move to higher temperatures or pressures above the critical point the sample remains in a single phase, but the density of the sample changes. Super-critical fluids (not really exactly a liquid or exactly a gas) have very interesting properties and are used in a variety of unique industrial processes. See the sidebar on page 433 in your textbook.

What is the phase on an axis? Any point where the pressure is zero, or the temperature is -273 degrees Celsius we must be careful attempting to describe the phase. So do not attempt to interpret any phases on the x-axis or on the y-axis of the graph.