1 / 11

Phase Changes

Phase Changes. How much energy does it take?. Changes in Phase. It takes energy to go from solid to liquid and liquid to gas. The change from one phase to another takes a little extra push of energy in order to get to that next phase. Energy Diagram for Phase Changes. Changes in Phase.

jacqui
Download Presentation

Phase Changes

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 How much energy does it take?

  2. Changes in Phase • It takes energy to go from solid to liquid and liquid to gas. The change from one phase to another takes a little extra push of energy in order to get to that next phase.

  3. Energy Diagram for Phase Changes

  4. Changes in Phase • The temperature does not change (along the plateaus), but notice that the heat is still being supplied. This allows for the change from one phase to another phase. • This is due to the intermolecular forces of attraction. These small forces take energy to allow the molecule to move from the other molecules

  5. Changes in Phase • H2O (s)  H2O (l) • ∆Hfus = 6.01kJ/mol • H2O (l)  H2O (s) • ∆Hsolid = - 6.01 kJ/mol • Notice the heats of enthalpies are just opposite in charge. • When water changes from solid to liquid it must absorb heat (+) • When water changes from liquid to solid it must lose heat (-)

  6. Changes in Phase • There are four types of energy phases changes • Molar Heat of Fusion- The heat absorbed by one mole of a substance in melting from solid to a liquid at constant temperature (∆Hfus) • Molar Heat of Solidification- The heat lost when one mole of a liquid solidifies (∆Hsolid) • Molar Heat of Vaporization- The amount of heat needed to vaporize one mole of a substance (∆Hvap) • Molar Heat of Condensation- The heat lost when one mole of a vapor condenses (∆Hcond)

  7. Here is an example! • How much heat is needed to change 28.0 grams of water at 0ºC to liquid water? ∆Hfus = 6.01 kJ

  8. Another Example • How much heat is needed to change 200.0 grams of water from 85ºC to 100ºC and change the water to steam? (Specific Heat of Water = 4.184 J/gºC ; ∆Hvap = 40.7 kJ/mol) • This requires two calculations: Slide 3

  9. Another Example (Cont.) • First you must calculate how much heat is needed to change the temperature from 85ºC to 100ºC. q = m x C x ∆T = (200.0g) x (4.184 J/gºC) x (15 ºC) = 12552 = 12600 J or 12.6 kJ Slide 3

  10. Another Example (Cont.) • Next you need to calculate how much heat is needed to convert the water from liquid to vapor. Now you add the two values together: 452 kJ + 12.6 kJ = 464.6 kJ = 465 kJ

  11. Energy Diagram for Phase Changes Back to Slide 8 Back to Slide 9

More Related