열역학 1,2 법칙

[김환기]

내가 하나님을 믿는 이유

1. 무에서 유를 만들 수 없다.

2. 무질서에서 질서를 만들 수 없다. 

3. 무생명에서 생명을 만들 수 없다. 

The First and Second Laws of Thermodynamics are two of the foundational principles governing physical systems and their behavior in terms of energy and entropy. Here is an overview of each:

First Law of Thermodynamics: (Law of Energy Conservation)

• Definition: The First Law of Thermodynamics states that energy cannot be created or destroyed, only transformed from one form to another. This is also known as the law of energy conservation. In a closed system, the total amount of energy remains constant, though it may change forms (e.g., from chemical energy to thermal energy).

• Mathematical Expression‎: The change in internal energy (ΔU\Delta UΔU) of a system is equal to the heat (QQQ) added to the system minus the work (WWW) done by the system:

  ΔU=Q−W\Delta U = Q - WΔU=Q−W
  • ΔU\Delta UΔU: Change in internal energy of the system.
  • QQQ: Heat added to the system.
  • WWW: Work done by the system.

• Implications:

  • It implies that energy is always conserved in an isolated system.
  • If a system gains or loses heat, it will result in a corresponding change in internal energy or the ability of the system to do work.

• Examples:

  • When you heat water in a pot, the thermal energy (heat) is absorbed by the water, increasing its internal energy, which can cause a temperature rise and eventually a phase change to steam.

Second Law of Thermodynamics: (Law of Entropy)

• Definition: The Second Law of Thermodynamics states that the total entropy of an isolated system can never decrease over time. It will either increase or, in ideal cases, remain constant in a reversible process. Essentially, natural processes tend to move towards a state of maximum entropy or disorder.

• Implications:

  • Directionality of Processes: The second law introduces the concept of irreversibility in natural processes. Heat will spontaneously flow from a hot object to a cold one, but not the other way around, without external work.
  • Efficiency Limits: It also places a limit on the efficiency of energy conversion systems, such as heat engines, where some energy is always "wasted" and lost as heat to the surroundings.
  • Arrow of Time: It gives a sense of time's direction since processes naturally progress towards greater entropy.

• Mathematical Expression‎: For a reversible process, the change in entropy (ΔS\Delta SΔS) is defined as:

  ΔS=ΔQrevT\Delta S = \frac{\Delta Q_{\text{rev}}}{T}ΔS=TΔQrev​​

  Where:

  • ΔQrev\Delta Q_{\text{rev}}ΔQrev​ is the reversible heat transfer.
  • TTT is the absolute temperature at which the heat transfer occurs.

  In any process, the total entropy change (ΔStotal\Delta S_{\text{total}}ΔStotal​) for an isolated system must satisfy:

  ΔStotal≥0\Delta S_{\text{total}} \geq 0ΔStotal​≥0

• Examples:

  • Melting Ice: When ice melts at room temperature, the structured ice crystals transition into a more disordered liquid state, increasing the entropy of the system.
  • Heat Engines: In steam engines, the conversion of heat energy to mechanical work is always accompanied by the loss of some energy as waste heat, which increases the entropy of the environment.

Summary of the Laws:

• First Law: Energy is conserved; it can be transferred or transformed but not created or destroyed.
• Second Law: Entropy, or disorder, of an isolated system will either increase or stay the same, and processes are naturally irreversible, with energy transformations being inherently inefficient.

Together, these laws form a basis for understanding how energy flows and changes in all physical systems, determining what processes are possible and setting fundamental limits on efficiency and work.