WHAT IS A PHASE DIAGRAM? It is a “map” that tells us which state(s) of matter (solid, liquid, gas) exist for a given set of temperature and pressure conditions.

Temperature A measure of the average kinetic energy (energy of motion) of particles (atoms or molecules) in matter in Celsius, Kelvin, or Fahrenheit.

Pressure A measure of how tightly matter is squeezed together in units of atmospheres (atm), bars, torrs, Pascals (Pa) or even pounds/in 2 (psi).

Two Allotropes of Carbon Which one is “stable” depends on both temperature and pressure!

Phase Diagram of Carbon Phase Diagrams are determined empirically by a large number of laboratory experiments! General Electric Co. helped determine the Carbon Phase Diagram.

Phase Diagram for Carbon Dioxide (CO 2 ) 1atm 10 atm 25  C In a 1 phase field, only one state is possible. On a phase boundary, two states will coexist. At a triple point, three states coexist.

Triple Point: A unique temperature and pressure at which three phases (usually solid, liquid, and gas) can exist together. Critical Point: The temperature and pressure at which gas and liquid merge together to form a supercritical fluid. Beyond this temperature, no amount of pressure will condense the gas to a liquid. Normal Melting Point – At 1 atm pressure, the temperature at which the solid melts to liquid. Normal Boiling Point – At 1 atm pressure, the temperature at which the liquid vaporizes to become a gas.

Dry Ice – CO 2 (s) vs. CO 2 (g) -78 °C, K, -109 °F

In general, 1)High pressures favor liquids and solids because the atoms are packed closer together (more dense). 2)Low pressures and high temperatures favor gases (less dense). 3) High temperatures favor liquids and gases because the atoms are less tightly packed, and are more mobile and energetic.

In other words….for most cases SolidsLiquids Temperature Pressure Gases

The H 2 O Phase Diagram  = 1.00 g/ml  =.92 g/ml  =.0006 g/ml

Note the negative slope of the ice-water phase boundary! What phase is most dense? Two ways to vaporize water….?? H 2 O Phase Diagram - continued

Fan n’ Pick Activity to Review Phase Diagrams Groups of 4 (mainly) 12 Cards Rotate Jobs 30 sec to answer 4 Coach if necessary, Paraphrase, then Praise 1 Fan the Cards and Run the Timer 2 Pick a Card and Read 3 Answer the Question Pass Card With Answer

Experiments to Determine the Phase Diagram of Boron From “Experimental Pressure-Temperature Phase Diagram of Boron: resolving the long standing enigma” Parakhonskiy, et al. Scientific Reports 1: article 96, 2011