Kinetic Energy, Temperature, Phase Changes

1. Kinetic Energy, Temperature, Phase Changes Chapter 13 Concepts

2. Kinetic Energy • particles have a wide range of K.E. • use the average kinetic energy of all particles • substances in different states of matter can have the same average K.E. • table salt, water, helium at room temperature • the Kelvin temp. of a substance is directly proportional to the average K.E. of the particles in a substance • 200 K has twice as much K.E. as 100 K

4. Temperature vs. Heat • temperature is a measure of the average kinetic energy in a system • heat is the energy transfer between two systems

6. Absolute Zero • particles would stop moving at a very low temperature • zero Kelvin is the temperature where motion of particles theoreticaly ceases • closest we have come is 0.5 x 10 –9 K

8. Phase Changes

9. LIQUID vaporization* *evaporation *boiling melting condensation freezing or solidification GAS SOLID sublimation = taking away heat (cooling down) = adding heat (heating up)

10. Vapor Pressure • measure of the force exerted by a gas above a liquid • dynamic equilibrium is reached when condensation equals evaporation

11. an increase in temperature increases the vapor pressure of the liquid • molecules have increased KE • more molecules will “escape”

13. Evaporation • a type of vaporization – the conversion of a liquid to a gas or vapor • evaporation is vaporization at the surface • only molecules with a certain amount of KE can escape from the surface

14. particles left behind have a lower KE • thus, evaporation is a “cooling process” • think of what happens when you sweat

15. Boiling Point • a type of vaporization where the vapor pressure of liquid is equal (to the external pressure on the liquid (atmospheric pressure) • when a liquid is heated to a temperature at which particles throughout the liquid have enough KE to vaporize

17. Boiling point and pressure • BP will change due to vapor pressure • different elevations will result in different BP • normal BP is at STP (101.3 kPa) Why must you cook things longer at higher elevations?

18. Melting Point • temperature at which a solid changes into a liquid • disruptive vibrations overcome attractive forces holding particles together

19. Sublimation • change from solid directly to liquid • when solid’s vapor pressure exceeds atmospheric pressure at room temperature • example: iodine, dry ice, air fresheners, freeze dried coffee

20. Condensation • conversion of a gas to a liquid • molecules with lower KE go back into liquid form

21. Freezing or Solidification • process in which a liquid turns into a solid when cold enough • most liquids freeze by crystallization • for most liquids, the freezing point and melting point are the same temperature

23. Phase Diagrams • provides conditions of pressure and temperature at which a substance can exist as a solid, liquid, and vapor • the triple point is where all three phases exist at once

25. Review of Concepts