Entropy

  1. Spontaneous change
    a change that has a tendency to occur without needing to be driven by an external influence
  2. The second law of thermodynamics
    energy spontaneously disperses from being localized to becoming spread out if it is not hindered from doing so
  3. Entropy
    the measure of the spontaneous dispersal of energy at a specific temperature: how much energy is spread out, or how widely spread out energy becomes, in a process
  4. At a given temperature, entropy _______ when energy is distributed into a system and ______ when energy is distributed out of a system
    • increases
    • decreases
  5. Spontaneous changes need not be fast and in some cases must be ______. However, nonspontaneous changes can only be brought about by _____ _____.
    • initiated
    • doing work
  6. Which formula would you use to calculate a change in entropy provided temperature is constant. What does the formula mean?
    • ΔS= qrev/T 
    • meaning: change in entropy equals (reversible energy transferred as heat) divided by (absolute/constant) temperature in Kelvin
  7. We always show the ____ of the entropy value
    sign (be it +/-)
  8. Name 3 things that can increase entropy
    • increasing heat
    • increasing volume
    • mixing with another substance
  9. When temp. is not constant but volume is which equation do you use?
    • explain (C)
    • ΔS=(C)(ln(T2/T1)
    • where C is the heat capacity (Cv if the volume is constant, Cp if the pressure is constant)
  10. When we have an isothermal expansion, with change in volume, state the series of equations (3) that leads to the final equation:
    • ΔS=nRln(V2/V1)
    • ΔS=Δqrev/T
    • =(-wrev)/T
    • =[nRTln(V2/V1)]/T
  11. The equation for change in entropy under the conditions: constant temp/ change in volume/pressure can be used for gases that expand for not just _______ but also _______ expansions between the same two states.
    • reversible
    • irreversible
  12. Explain why the constant temperature & change in volume/pressure can do do this:
    • ΔS=nRln(V2/V1) =nRln(P1/P2)
    • ideal gas law, specifically Boyle's law which states V2/V1=P1/P2. In other words, volume and pressure are inversely proportional at constant temperature.
  13. What are the units for entropy
    J⋅K-1
  14. What do you do when calculating entropy and neither temperature nor volume are constant?
    Break the question into appropriate steps. Some values maybe constant at certain points during the process or different at certain points. Use appropriate equations to find the relevant enthalpy values and sum them up.
  15. when dealing with changes in temp in entropy calculations, what units should the values be in when doing natural logs?
    kelvin
  16. A liquid vaporizes until its _____ _____ has reached a certain value, called its vapor pressure. As the liquid is heated, its vapor pressure increases until it is equal to the ______ ______. At that temperature, which is called the _____ temperature, the liquid ______.
    • partial pressure
    • external pressure 
    • boiling temp
    • boils
  17. To use the equation ΔS=qrev/T, to calculate the entropy change for a substance undergoing a transition from one phase to another at its transition what three facts do we need to factor in?
    • At the transition temp (such as boiling point for vaporization), the temp of the substanc remains constant as heat is supplied. 
    • At the temp of a phase transition, the transfer of heat is reversible
    • Because the transition takes place at constant pressure (for instance, 1 atm) the heat supplied is equal to the change in enthalpy of the substance
  18. At the transition temp, all the energy supplied is used to drive the _____ transition, such as the conversion of liquid into _____, instead of raising the ______. The T in the denominator of the derivation of ΔS=qrev/T is therefore a _____ and may be set equal to the _______ temperature
    • phase transition
    • vapor
    • temp
    • constant
    • transition temp
  19. At the temp of phase transition, the transfer of heat is ______ provided the external pressure is ______, raising the temperature of the surroundings an infinitesimal amount results in complete _______, and lowering of the temperature causes complete _______.
    • reversible
    • constant
    • vaporization
    • condensation
  20. The entropy of vaporization, ΔSvap, is the change in entropy per ____ of molecules when a substance changes from _____into a _____. This is basically the amount of _____ required per mole to vaporize the liquid at _____ pressure. State the new derived equation for calculating entropy of vaporization (ΔSvap) assuming we are at boiling point
    • mol
    • liquid 
    • vapor
    • heat 
    • constant 
    • ΔSvap= ΔHvap/Tb
  21. When the liquid and the vapor are in their standard states (both ____ and both at ___ bar) and the boiling temp is at 1 bar, this is referred to as the standard entropy of vaporization (____).  Keep in mind that this is the change in molar entropy at the temperature of the ______ point and can be different from its value at 298K.
    • pure & at 1 bar
    • ΔSvap°
    • boiling
  22. Trouton's rule explains why many standard entropies of vaporization are close to _____ at their boiling points. This is because approximately the same increase in _____ _____ occurs when any liquid is converted into _____, and so we can expect the change in entropy values to be relatively similar.
    • 85J⋅K-1mol-1
    • postional disorder
    • vapor
  23. Substantial departures from trouton's rule indicate that the molecules have a more _____ arrangement than expected of most liquids, and so there is a greater increase in _____ when they vaporize.
    • orderly 
    • disorder
  24. When calculating standard entropy of fusion we recognize that this value is attained as a _____ transitions into a _____. This would occur at a constant temperature, the ______ point (aka the _____ point) and the amount of heat necessary to make this happen would be the _____ of fusion
    • solid
    • liquid
    • freezing
    • melting
    • enthalpy
  25. The equation for standard entropy of fusion:
    ΔSfus°=ΔHfus°/Tf
  26. When calculating the entropy of vaporization at temperatures other than the normal boiling point what 4 steps do we follow?
    • heat the liquid to its normal boiling point (ΔS=Cm*ln(T2/T1)
    • allow it to vaporize (ΔSvap= ΔHvap/Tb)
    • cool the vapor back to the temp (with a monatomic/linear/nonlinear or Cv,m=3/2R,5/2R or 3R. Can also use Cp,m=5/2R, 7/2R or 4R)
    • sum up all the ΔS values from steps 1-3
  27. Values like Hvap and Hfus are reported as _____ & _____ (units), respectively, during calculations
    • J*mol-1
    • J*mol-1
  28. The 3/2R, 5/2R, 4R etc dilemma is something we run into when we try to attain heat capacity of something vaporized or in a ______ state
    gaseous
Author
chikeokjr
ID
327644
Card Set
Entropy
Description
Week 2 Ch 9 pt 1
Updated