{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

10_1425_web_Lec_36_Entropy

# 10_1425_web_Lec_36_Entropy - Entropy Physics 1425 Lecture...

This preview shows pages 1–7. Sign up to view the full content.

Entropy Physics 1425 Lecture 36 Michael Fowler, UVa

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
First and Second Laws of Thermodynamics A quick review…. First Law: total energy conserved in any process : joules in = joules out Second Law : heat only flows one way, and we can’t turn heat into just work, etc… This Second Law sounds a bit vague compared with the First Law! Can it be stated more precisely, more numerically , like the First Law?
Back to the Carnot Cycle… But this time think of it as showing two different routes from a to c : abc and adc . We know that the total change in a state variable, P , V or T , from a to c doesn’t depend on which path we take. BUT the total heat flow into the gas DOES depend on path! The “amount of heat” in the gas is meaningless. a b d c

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Back to the Carnot Cycle… However, the heat input Q H along abc is related to the heat input Q L along adc : Clausius defined “en t ropy” by: the entropy change along a half Carnot cycle is This doesn’t depend on path! a b d c C H HC Q Q TT = Q S T ∆=
Different Reversible Paths from a to c Now suppose we follow the path aefgc , where efgd is a little Carnot cycle. Then the entropy change efg is the same as edg , so the total entropy change along this path from a to c is the same as adc . By adding lots of little Carnot zigzags like this, we can get from any reversible path from a to c to any other reversible path, and define the entropy change from a to c unambiguously as: z a d c e b f g . revers path dQ S T ∆=

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
What about Irreversible Paths? Suppose we have an insulated container with a partition down the middle , ideal gas on one side, vacuum on the other. The partition is suddenly removed—gas fills the whole space. What happens to the gas temperature?
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### Page1 / 23

10_1425_web_Lec_36_Entropy - Entropy Physics 1425 Lecture...

This preview shows document pages 1 - 7. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online