Study Buddy Unit II- Constant Velocity

Study Buddy: Energy and Phase Changes

Terms / Description /

Picture

/ Symbol/Unit
Heat / Amount of thermal energy transferred from one system to another
http://commons.wikimedia.org/wiki/File:Hand_left.svg
http://www.clker.com/cliparts/i/7/R/z/J/P/ice-cube-md.png / / Q/ Joules (J) or calorie (cal)
Total Internal Energy / Describes the total amount of energy in a system. Equals the sum of kinetic and potential energies.
Kinetic Energy: due to motion of particles
Potential Energy: due to relative position of particles / KE or Ek
high low / IE/ Joules (J) or calorie (cal)
PE or Ep
high low
far apart close
Endothermic Process / System absorbs energy from surroundings
Phase changes: melting, vaporizing, subliming
http://sweetclipart.com/cooking-pot-coloring-page-2015 / Stove top or fire / +Q for system
Exothermic Process / System releases heat to surroundings
Phase changes: freezing, condensing, depositing / Bowl of ice / -Q for system
Vapor Pressure / Pressure exerted by the vapor particles over a liquid or solid substance at equilibrium. / http://www.anesthesia2000.com/physics/Chemistry_Physics/physics15.htm

How does thermal energy transfer cause phase changes?

As a solid or liquid is heated, the thermal energy is used to increase the kinetic and potential energy of the particles (particles moving faster and farther apart). When a liquid or gas is cooled, the thermal energy transferred to the surroundings reduced the kinetic and potential energies of the particles.

Melting = _0_°C Boiling = _100_°C

Translating to a Heating or Cooling Curve

100°C

0°C

Time or Energy added

Label where PE and KE are changing on the heating curve above.

Heating Curve for Water Cooling Curve for Water

100°C 100°C

0°C 0°C

Heat added Heat removed

Does the total internal energy of 10.g of water vapor change as it becomes ice? Why?

The total internal energy decreases as the water vapor condenses and freezes to form ice. As a gas, the particles have high kinetic and potential energies because they are moving quickly and relatively far apart from each other. Solid particles are closer together and moving slower. The energy that the water loses is given off to the surroundings.

How would a heating or cooling curve for a mixture look different than a pure substance?

The mixture would not be as “crisp” as that for the pure substance since the different components have phase changes at different points. A line is shown in blue on the cooling curve above to represent a theoretical mixture.

Vapor Pressure and Boiling Water

Houston Mt. Everest

Mt. Everest

8850 m above 1 atm 0.33 atm

sea level bp=100°C bp=71°C

Houston

0 m above sea level

Why can water boil at a lower temperature on Mt. Everest than in Houston?

The atmosphere at Mt. Everest has less air particles resisting the water particles going from liquid to gas (the air particles are further apart on Mt. Everest) therefore the water particles do not need as much energy to move to the gas phase. There is less external pressure, so a lower temperature will be able to create a vapor pressure equal to the atmospheric pressure.

Phase Diagram for Water