Thermodynamics and daily life

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    Life Thermodynamics
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Discussion Overview

The discussion revolves around the concepts of thermodynamics, specifically focusing on internal energy, enthalpy, entropy, and their significance in real-life applications. Participants express confusion about the definitions and relationships between these terms, as well as their relevance to daily life and engineering.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant expresses uncertainty about the significance of thermodynamic concepts like internal energy, enthalpy, and entropy, seeking real-life references.
  • Another participant emphasizes the foundational role of thermodynamics in the industrial revolution and encourages asking specific questions for better understanding.
  • A participant seeks clarification on the definitions of heat, enthalpy, internal energy, and their interrelations, particularly under varying pressure conditions.
  • One response notes that there are no absolute values for energies when applying the first law of thermodynamics, highlighting the importance of changes between states rather than fixed values.
  • Another participant distinguishes between internal energy and enthalpy, explaining that they are different thermodynamic potentials and that heat refers to the energy change during a process.
  • A participant describes internal energy as the sum of kinetic and potential energies of particles, while defining entropy as a measure of disorder and enthalpy as the total energy of a system.
  • Discussion includes the relationship between enthalpy and pressure, with a participant stating that an increase in pressure leads to an increase in enthalpy if other factors remain constant.
  • One participant suggests that practical applications of thermodynamics can be found in engineering literature and courses, indicating its relevance to various engineering fields.
  • A later reply mentions the importance of experimentation in understanding thermodynamics and references statistical mechanics as a helpful area of study.

Areas of Agreement / Disagreement

Participants express various levels of confusion and differing interpretations regarding the definitions and relationships of thermodynamic concepts. There is no consensus on the clarity of these concepts or their applications in real life.

Contextual Notes

Participants highlight limitations in understanding due to the complexity of thermodynamic principles and the need for a clear reference state when discussing energy changes. The discussion reflects ongoing uncertainties and varying interpretations of the concepts involved.

Who May Find This Useful

This discussion may be useful for students and professionals in physics, engineering, and related fields who are seeking clarification on thermodynamic concepts and their applications.

Chemer
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Hi everyone,
I'm reading thermodynamics and I can remember what's internal energy, enthalpy, entropy etc but I'm not sure whether I understand it completely or not as I couldn't find any real life reference to these concepts and what's the significance of learning all these things? Why we name the same thing differently as heat, enthalpy, internal energy etc? Please help me understand this.
Thanks:)
 
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Chemer said:
Please help me understand this.
"This" (thermo) is the foundation of the industrial revolution.
When you have specific difficulties with specific concepts, bring them to PF, and people are going to be more than happy to coach you through them. Check the PF posting guidelines for specifics on selecting sub-forums, and material to include in your requests for assistance.
 
Sorry for not asking the question clearly. I wanted to ask,
I'm confused about the terms heat, enthalpy, internal energy and total energy of the system. internal energy is the heat energy contained in a system, work is the mechanical energy(P.E stored in system), heat is the internal energy transferred between system and the surrounding? And enthalpy?? Is it the total energy of the system?? Or its the heat contained in a system at constant pressure? What happens to enthalpy if there's change in pressure? What's its relation with pressure?
Thanks.
 
Chemer said:
total energy
Chemer said:
heat energy contained
Chemer said:
mechanical energy(P.E stored in system),
Chemer said:
heat contained in a system at constant pressure
First source of confusion: there are no absolute ("total" or "stored") values for energies when working with the first law; you are doing bookkeeping only upon changes in these energies between (or among) two (or more) states of a system. Generally there is some initial or reference state (or you define one) to which you add or subtract work or heat.
 
If you really want to know more about real life applications, you should read more engineering books. In fact, many engineering courses have compulsory thermodynamics. You would learn that thermo is crucial to many parts of engineering.

Heat, enthalpy, and internal energy are so different. Firstly, internal energy U and enthalpy H are two different thermodynamic potentials that are minimized under different conditions, and U = H - pV. Secondly, heat Q refers to the internal energy change involved in a process which depends on the process, whereas internal energy itself is a state function which only depends on the state of the system. 1st law is usually written as dU = dW + dQ, so they are not exactly the same.
 
Internal energy: The sum of the kinetic and potential energies of the particles of a system.
Entropy: Quite simply put, it's a measure of the "disorderliness" of the particles/components of a system.(The degree of random placement which is more probable as a result of non-directional energy presence, such as that caused by diffusion)
Enthalpy: The total energy of a system.
It is worthwhile mentioning that only changes in energies of a system are observable. For convenience, we often end up defining a standardized "0" from which changes of a system are measured. You commonly use thermodynamic understanding in daily life without actually realizing it: by knowing that a teaspoon of water heats up faster than a pan full of it at the same initial temperature, for example.
 
Chemer said:
...What's its relation with pressure?
Thanks.
Enthalpy = Internal Energy + (Pressure)*(Volume)
If pressure goes up, and everything else stays the same, then enthalpy must go up.
 
Here is a great place to start if you haven't already found this site:
http://hyperphysics.phy-astr.gsu.edu/hbase/heacon.html#heacon
Thermo is a hard subject to study no matter how much you read, experimentation always helps. I like to think about the combustion engine. But to really get a feel for why it all works statistical mechanics helps, they math is a little funny to decipher but the concepts are rock solid and make sense.
In these lectures below are some really interesting demonstrations of thermodynamics and great explanations

Prof. C. J. Cramer (University of Minnesota)
 

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