state of matter

States

• state of matter (or phase of matter)
  • gaseous state
    • gas – “a state of matter with neither fixed volume nor fixed shape” (Wikipedia)
    • vapor
  • liquid state
    • ”a state of matter with a definite volume but no fixed shape” (Wikipedia)
    • liquid (n. and adj.) (נוזלי, נוזל)
  • soild state
  • supercritical fluid (SCF)

Gas

• elemental gases
  • monatomic: noble gases
  • diatomic: $\mathrm{H}{}_2,\mathrm{N}{}_2,\mathrm{O}{}_2,\mathrm{F}{}_2,\mathrm{Cl}{}_2$
• Gas laws
• inert gas (גז אינרטי)

Vapor

• vapor (אד, אדים)
  • “a substance in the gas phase at a temperature lower than its critical temperature, which means that the vapor can be condensed to a liquid by increasing the pressure on it without reducing the temperature of the vapor” (Wikipedia)
  • “gaseous state of any substance that normally exists as a liquid or solid” (Brown, 2012)
  • water vapor (or aqueous vapor)
    • steam

Phase diagram

(source: commons.wikimedia.org)

• phase diagram
  • lines of equilibrium (or phase boundaries)
  • The critical point (specifically liquid–vapor critical point) is the point $(T_c,P_c)$ in which the liquid–gas equilibrium curve ends. Beyond this point, the distinction between liquid and gas vanishes, and the substance becomes a supercritical fluid.
    • $T_c$ is the critical temperature
    • $P_c$ is the critical pressure
  • The triple point is the point $(T_{tp},P_{tp})$ in which all three phases coexist in dynamic equilibrium
• standard temperature and pressure (STP)
  • until 1982: $T=273.15\mathrm{K},P=1\text{atm}$
  • since 1982: $T=273.15\mathrm{K},P=1\text{bar}$
• threshold temperatures for a substance at a given pressure:
  • melting point (or liquefaction point) (נקודת התכה, נקודת היתוך)
  • freezing point (or crystallization point) (נקודת קיפאון)
  • boiling point (נקודת רתיחה)
    • “the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor” (Wikipedia)
      • the temperture $T_{\text{b}}$ such that $P_{\text{vap}}(T_{\text{b}})=P_{\text{ext}}$
    • stronger intermolecular forces require more energy (higher temperature) to overcome, resulting in higher boiling points
    • normal boiling point (or atmospheric boiling point)
    • standard boiling point

Example: water

(source: commons.wikimedia.org)

Phase transition

(source: commons.wikimedia.org)

• phase transition (or phase change) (מעבר פאזה)
  • melting (התכה, היתוך, (המסה))
  • condensation (התעבות)
  • vaporization
    • evaporation (התאיידות, התאדות, אידוי)
    • boiling (or ebullition) (הרתחה)
  • sublimation (המראה, סובלימציה)
  • freezing (הקפאה, התמצקות)
• see latent heat

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• determining state of matter at room temperature:
  • ionic compound → usually solid
  • network solid → almost always solid
  • alloy or pure metal → usually solid (exception: Hg is liquid)
  • molecular compound:
    • bigger/heavy molecule → higher boiling point
    • higher polarity → higher boiling point
    • capable of hydrogen bonding → higher boiling point
• volatility (נדיפות)
  • weak IMFs → high volatility (evaporates easily) → low boiling point
  • strong IMFs → low volatility (evaporates slowly) → high boiling point
  • higher vapor pressure ↔ higher volatility

References

• Brown, Theodore L. (2012). Chemistry. Prentice Hall.