What is this called?
A phase diagram
What phases are shown?
solid, liquid, gas, supercritical fluid
What relatively common phase of matter is not shown, where would you expect it to be and why is it not shown?
Plasma
It would be on the right side of the diagram, at higher temperatures.
It is not shown because carbon dioxide cannot exist as a plasma. It would break down into its individual atoms first.
What is the structure of the substance shown in this diagram?
This is a phase diagram for carbon dioxide which is made of 2 oxygen atoms, each bound to a carbon atom by a double bond.
What is the solid phase of this substance called?
Solid carbon dioxide is called dry ice.
What scale is used for pressure?
A logarithmic scale
What unit is used for temperature and what other units might have been used?
Kelvin is used in this diagram.
Celcius and Fahrenheit are other common temperature scales.
What unit of measure is used for pressure and what other units might have been used?
Pressure is measured in bars in this diagram.
Pressure has many different units that are commonly used in different situations.
| Unit | Equivalent to atmospheric pressure | Uses |
| 1 atmosphere (atm) | 1 atm | chemistry |
| bar | 1.01 bar | weather |
| millibar (mbar) | 1013 mbar | weather |
| torr | 760 torr | vacuum chambers |
| pounds per square inch (psi) | 14.7 psi | tire pressure |
| Pascal (the SI unit of pressure = N/m2) | 101,325 Pa | SI units, engineering, weather |
| kiloPascal (kPa) | 101.325 kPa | weather |
| millimeters of mercury (mm Hg) | 760 mm Hg | blood pressure cuffs |
| centimeters of water (cm H2O) | 1033 cm H2O | ventilators |
Where is room temperature and standard atmospheric pressure on this diagram?
Room temperature is about 20°C, which is 293 K.
1 atm = 1.01 bar
Therefore, the point with standard temperature and pressure is barely on this diagram, just above the lower edge and just to the left of the 300 K tick mark.
What is the triple point?
It is the pressure and temperature at which the substance can exist in equilibrium as a solid, liquid and gas.
Approximately what is the triple point on this diagram?
The triple point of carbon dioxide is 216 K and 5.16 atm.
Why is the triple point closer to the 10 bar tick mark than the 1 bar tick mark on the diagram?
It is a logarithmic scale. 100 = 1, 101 = 10. Halfway between is 100.5 = 3.16…
The triple point of carbon dioxide is at 5.17 bar. The log10(5.17) = 0.71…, much closer to 1 than to 0.
What is the consequence of the triple point being as high as it is?
Carbon dioxide cannot exist at room temperature. Instead, it sublimates directly from gas to solid, thus being “dry ice”.
What are the phase transitions from solid->liquid, liquid->solid, liquid->gas, gas->liquid, solid->gas and gas->solid called?
| From | To | Process |
| Solid | Liquid | Melting |
| Liquid | Solid | Freezing |
| Liquid | Gas | Evaporation (Boiling) |
| Gas | Liquid | Condensation |
| Solid | Gas | Sublimation |
| Gas | Solid | Deposition |
What is the difference between evaporation and boiling?
Evaporation occurs any time that a liquid changes to a gas. This can occur at any temperature.
Boiling occurs at the temperature at which the vapor pressure of the liquid reaches the atmospheric pressure.
CoMo Science 
Leave a comment