entropy n.
Download
Skip this Video
Download Presentation
Entropy

Loading in 2 Seconds...

play fullscreen
1 / 8

Entropy - PowerPoint PPT Presentation


  • 86 Views
  • Uploaded on

Entropy. Energy Quality. You are offered 1000 J of energy. Would you rather have it as A) mechanical work B) frictional work C) heat from an object at 1000 K D) heat from an object at 300 K. A Carnot cycle found a relationship between the temperatures and heat.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Entropy' - ulric-logan


Download Now 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.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
energy quality
Energy Quality
  • You are offered 1000 J of energy. Would you rather have it as
  • A) mechanical work
  • B) frictional work
  • C) heat from an object at 1000 K
  • D) heat from an object at 300 K
closed cycle
Closed Cycle
  • Any closed cycle can be approximated by a sum of Carnot cycles.
  • On a PV diagram this is any reversible cycle.
    • The heat to temperature ratios can be added.
entropy defined
Entropy Defined
  • Entropy is defined as the heat flow at an absolute temperature.
  • The path doesn’t matter, so entropy is a macroscopic state variable.
melting ice
The latent heat of ice is 79.7 kcal/kg.

What is the change of entropy for a very slowly melting 1.00 kg piece of ice?

What is the change in entropy for the surroundings?

Find the heat transfer.

Q = mL = 79.9 kcal

Find the entropy change.

DS = Q/T = 0.292 kcal/K

The process is reversible.

DSsurr = -0.292 kcal/K

Melting Ice
mixing
A sample of 50.0 kg water at 20.0 C is mixed with 50.0 kg water at 24 C.

Estimate the change in total entropy.

Find the heat transfer. There are equal amounts of heat in each sample.

Q = mcDT = 100. kcal

Find the entropy change in each sample using the average temperature.

DSH = Q/T = -100. kcal/296K = -0.338 kcal/K

DSL = Q/T = +100. kcal/294K = +0.340 kcal/K

The difference is the net change.

DS = +0.002 kcal/K

Mixing
second law iii
Second Law III
  • The second law of thermodynamics can be described in terms of entropy:

The entropy of an isolated system never decreases. It only stays the same for reversible processes.