1 / 25

Sublimation : solid  gas. Vaporization : liquid  gas.

Phase Changes. Sublimation : solid  gas. Vaporization : liquid  gas. Melting or fusion : solid  liquid. Deposition : gas  solid. Condensation : gas  liquid. Freezing : liquid  solid. Phase Changes. ENERGY ASSOCIATED WITH HEATING CURVES. Topics. Vapor Pressure

miracle
Download Presentation

Sublimation : solid  gas. Vaporization : liquid  gas.

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Phase Changes • Sublimation: solid  gas. • Vaporization: liquid  gas. • Melting or fusion: solid  liquid. • Deposition: gas  solid. • Condensation: gas  liquid. • Freezing: liquid  solid.

  2. Phase Changes

  3. ENERGY ASSOCIATED WITH HEATING CURVES

  4. Topics • Vapor Pressure • Normal Boiling Point • Normal Freezing • Specific Heat • Enthalpy (Heat) of Vaporization • Enthalpy (Heat) of Fusion

  5. Vapor Pressure • THE PRESSURE OF A VAPOR IN EQUILIBRIUM WITH ITS LIQUID (OR ITS SOLID)

  6. NORMAL BOILING POINT & FREEZING POINTS • NORMAL BOILING PT. - THE TEMPERATURE @WHICH VAPOR PRESSURE = 1 atm • NORMAL FREEZING PT. – THE TEMPERATURE @ WHICH THE VAPOR PRESSURE OF THE SOLID AND THE LIQUID ARE THE SAME

  7. Heat Capacity aka Specific Heat (C) • Specific Heat (C) = the amount of energy required to raise the temperature of 1 gram of substance 1 degree celcius

  8. Specific Heat (C) aka Heat Capacity • Units for:specific heat (C) = J/g-oC where J = joules oC = temperature in oC g = mass in grams

  9. Specific Heat (C) Values(aka Heat Capacity) • Example: Water • LIQUID: CLiq = 4.18 J/ (oC . g) • LIQUID: Csol = 2.09 J/ (oC . g) • LIQUID: Cgas = 1.84 J/ (oC . g)

  10. Use of Specific Heat • q = mCDT • q = gm substance x specific heat x DT • where: • M = mass of substance in grams • q = amount of heat (energy) • C = specific heat • And DT = change in temperature

  11. Enthalpy of Vaporizationaka heat of vaporization (DHvap) • Is the amount of heat needed to convert a liquid to a vapor at its normal boiling point

  12. Enthalpy of Fusion aka heat of fusion (DHfus) • Is the amount of heat needed to convert a solid to a liquid at its normal melting (freezing) point

  13. Units for DHvap, DHfus and heat(q) Heat of fusion DHvap = kJ/mol Heat of vaporization DHfus = kJ/mol Heat (q) = Joules

  14. Therefore: • To come up with Joules which is the unit of heat, if: (1) DH is given, then: qvap = DHvap x moles and qfus = DHfus x moles (2) Specific heat (C) is given, then: q = mCDT

  15. Sample Problem • Calculate the enthalpy change upon converting 1 mole of ice at -25 oC to steam at 125 oC under a constant pressure of 1 atm? The specific heats are of ice, water and steam 2.09 J/g-K for ice, 4.18 J/g-K for water and 1.84 J/g-K for steam. For water, DHfus= 6.01 kJ/mol, and DHvap = 40.67kJ/mol. • Note: The total enthalpy change is the sum of the changes of the individual steps.

  16. Take Home Quiz • Do Problem 11.34, page 444 • Due Wednesday at the beginning of class, Dec. 1 • Must show work for full credit • Individual work not required

  17. HEATING CURVES • ENERGY ASSOCIATED WITH HEATING CURVES • During a phase change, adding heat causes no temperature change.

  18. Phase Changes • Critical Temperature and Pressure • Gases liquefied by increasing pressure at some temperature. • Critical temperature: the minimum temperature for liquefaction of a gas using pressure. • Critical pressure: pressure required for liquefaction.

  19. Phase Diagrams • Phase diagram: plot of pressure vs. Temperature summarizing all equilibria between phases. • Given a temperature and pressure, phase diagrams tell us which phase will exist. • Any temperature and pressure combination not on a curve represents a single phase.

  20. Phase Diagrams

  21. Phase Diagrams The Phase Diagrams of H2O and CO2

More Related