Skip to ContentGo to accessibility pageKeyboard shortcuts menu
OpenStax Logo
University Physics Volume 2

Summary

University Physics Volume 2Summary
Search for key terms or text.

Summary

4.1 Reversible and Irreversible Processes

  • A reversible process is one in which both the system and its environment can return to exactly the states they were in by following the reverse path.
  • An irreversible process is one in which the system and its environment cannot return together to exactly the states that they were in.
  • The irreversibility of any natural process results from the second law of thermodynamics.

4.2 Heat Engines

  • The work done by a heat engine is the difference between the heat absorbed from the hot reservoir and the heat discharged to the cold reservoir, that is, W=Qh−Qc.W=Qh−Qc.
  • The ratio of the work done by the engine and the heat absorbed from the hot reservoir provides the efficiency of the engine, that is, e=W/Qh=1−Qc/Qh.e=W/Qh=1−Qc/Qh.

4.3 Refrigerators and Heat Pumps

  • A refrigerator or a heat pump is a heat engine run in reverse.
  • The focus of a refrigerator is on removing heat from the cold reservoir with a coefficient of performance KR.KR.
  • The focus of a heat pump is on dumping heat to the hot reservoir with a coefficient of performance KP.KP.

4.4 Statements of the Second Law of Thermodynamics

  • The Kelvin statement of the second law of thermodynamics: It is impossible to convert the heat from a single source into work without any other effect.
  • The Kelvin statement and Clausius statement of the second law of thermodynamics are equivalent.

4.5 The Carnot Cycle

  • The Carnot cycle is the most efficient engine for a reversible cycle designed between two reservoirs.
  • The Carnot principle is another way of stating the second law of thermodynamics.

4.6 Entropy

  • The change in entropy for a reversible process at constant temperature is equal to the heat divided by the temperature. The entropy change of a system under a reversible process is given by ΔS=∫ABdQ/TΔS=∫ABdQ/T.
  • A system’s change in entropy between two states is independent of the reversible thermodynamic path taken by the system when it makes a transition between the states.

4.7 Entropy on a Microscopic Scale

  • Entropy can be related to how disordered a system is—the more it is disordered, the higher is its entropy. In any irreversible process, the universe becomes more disordered.
  • According to the third law of thermodynamics, absolute zero temperature is unreachable.
PreviousNext
Order a print copy
Citation/Attribution

This book may not be used in the training of large language models or otherwise be ingested into large language models or generative AI offerings without OpenStax's permission.

Want to cite, share, or modify this book? This book uses the Creative Commons Attribution License and you must attribute OpenStax.

Attribution information
  • If you are redistributing all or part of this book in a print format, then you must include on every physical page the following attribution:

    Access for free at https://openstax.org/books/university-physics-volume-2/pages/1-introduction

  • If you are redistributing all or part of this book in a digital format, then you must include on every digital page view the following attribution:

    Access for free at https://openstax.org/books/university-physics-volume-2/pages/1-introduction

Citation information

© Jan 27, 2025 OpenStax. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution License . The OpenStax name, OpenStax logo, OpenStax book covers, OpenStax CNX name, and OpenStax CNX logo are not subject to the Creative Commons license and may not be reproduced without the prior and express written consent of Rice University.