From APChempedia, the free AP prepbook

    Phase diagrams, vapor pressure, and heating/cooling curves are all topics that pertain to phases or states of matter and changes associated with them. Phase diagrams express the physical state of a substance in terms of its temperature and pressure exerted.Vapor pressure is the relative pressure exerted by the vapor of a substance. Heating/cooling curves illustrate the phase changes a substance undergoes as energy (heat) is added to the substance in the case of a heating curve, or as energy is emitted from the substance as in the case of a cooling curve.

Contents [hide] 1 Overview         1.1 Phase Diagrams 1.2 Vapor Pressure 1.3 Heating/Cooling Curves 3 Key Terms 4 Works Cited 5 Further Reading 6 About Our Lab Group

 

Overview

 

Phase Diagrams

    Phase diagrams show the states of matter of a substance with respect to the temperature and pressure. The triple point corresponds to the temperature and pressure where all three phases of a substance exist. On the other hand, the critical point refers to the temperature above which a gas cannot be liquefied no matter how much pressure is applied to it.

 

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Vapor Pressure

    Vapor pressure is the pressure of the vapor above the liquid at equilibrium. It is caused by evaporation at the surface of the liquid. The evaporated molecules fly around in the air and can rejoin the liquid. At equilibrium vapor pressure, there is no net change in the vapor pressure even though molecules are constantly evaporating and combining back into the liquid. High vapor pressures are caused by molecules with weak intermolecular forces and high energy.

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Heating/Cooling Curves

 

Heating and cooling curves are a graph of a substance's phase changes over time as heat is added or lost. In a heating curve, an upward sloping line represents the solid, liquid, and gaseous phases, while a horizontal line represents the melting and vaporizing processes. In a cooling curve (the opposite of a heating curve), a downward sloping line passes through the substance's gaseous, liquid, and solid phases. A horizontal line shows the time it takes for the substance to condense and solidify. Heating and cooling curves show that no temperature change takes place while a substance is in the process of a phase change.

 

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Key Terms

• Phase Diagram - a graphical representation of the phase of a substance at different combination of temperatures and pressures.
• Phase Change - a change in the physical state of matter of a substance, phase changes are dependent on temperature and pressure.
• Critical Point - the point on a phase diagram where the temperature and pressure have reached their end point of the liquid-vapor line and thus a phase boundary ceases to exist.
• Critical Pressure -the lowest pressure needed to liquefy a substance at its critical temperature.
• Critical Temperature - the temperature where vapor cannot be liquefied, despite the amount pressure applied.
• Triple Point - the point on a phase diagram where all three states of matter coexist.
• Vapor Pressure - the pressure of the vapor over a liquid or solid when at equilibrium.
• Vaporization (evaporation) - the process whereby liquid is physically transformed into gas.
• Heat of Vaporization (Enthalpy of vaporization (ΔHvap) - the energy (heat) needed to convert 1 mole of a liquid into gas at a pressure equal to one atmosphere. 
• Condensation - the process in which a substance changes physical state or phase from that of a gas into a liquid. 
• Equilibrium - the condition where chemical reaction occurs at rates forwards and backwards. In a physical sense, when a particular system is undergoing forward and backward physical equal change, causing no overall change in the amount of a substance at either state.
• Equilibrium Vapor Pressure - the pressure of the vapor present when a system is at equilibrium.
• Sublimation - the physical process by which a substance goes directly from the solid to the gaseous state without passing through the liquid state. Typically, Sublimation occurs at low pressures. 
• Heating Curve - a graphical representation of the phases that a substance undergoes as a constant amount of heat (energy) is added to it over a period of time.
• Cooling Curve- a graphical representation of the phases that a substance undergoes as the substance loses energy (heat) over a period of time.
• Enthalpy (heat) of Fusion (ΔHfus) -the amount of heat energy that must be added to 1 mole of a particular substance for it to change phases from solid to liquid or liquid to solid.
• Normal Boiling Point - the boiling point when the vapor pressure of a liquid is equal to one atmosphere.
• Normal Melting Point - the melting point when the vapor pressure of a liquid is equal to one atmosphere.
• Supercooled - to cool a liquid below is freezing point; however, not freezing it  
• Superheated - to heat a liquid above its boiling point; however, not boiling it

 

Works Cited

Further Reading

• Coulter, Bruce. "Mr. Coulter's AP Chemistry Lectures." Lowell High School. 13 Mar. 2006. 30 May 2009.

  <http://www.mrcoulter.com/lectures.htm>.

• Nave, Carl R. "Phase Changes." HyperPhysics. 2006. Georgia State University. 30 May 2009
  <http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/phase.html>.

• Nave, Carl R. "Vapor Pressure." HyperPhysics. 2006. Georgia State University. 30 May 2009
  <http://hyperphysics.phy-astr.gsu.edu/Hbase/Kinetic/vappre.html>.

• Nelson, Stephen A. "Two Component Phase Diagrams." Tulane University. 2 Apr. 2003. 30 May 2009
  <http://www.tulane.edu/~sanelson/geol212/2compphasdiag.html>.

• Zetie, Ken. "Heating and Cooling Curves." Practical Physics. 22 Feb. 2008. Nuffield Curriculum
  Centre. 30 May 2009 <http://www.practicalphysics.org/go/SubmitWebsiteExperiment_207.html>.

 

About Our Lab Group

• 
• So, this picture pretty much sums up our AP Chem lab group

• Ravi Patel (lower right corner), looks like he is preparing to strangle Timoslav after he left the toxic iodine bottle open.

• Samantha Ngo (lower left corner) and Leana Tran-Le (center) can’t seem to contain their excitement for AP Chem.

• Then, there is Timothy (or Timoslav as we prefer). Like always, he is as cool as a cucumber. We’ll see if he can maintain that composure next year at UC Berkeley.

• Random guy standing behind Leana. We really don't know who he is or why he wanted to be in our lab picture. He probably wanted to join our lab group because its just hella cool.

 

Webpage Created by Ravi Patel, Timothy 'Timoslav' Jang, Leana Ngoc Tran-Le, & Samantha Ngo Mods 14/15 May 30, 2009.