the second law of thermodynamics

Examples of the second law of thermodynamics in the following topics:

• The Second Law

  • The second law of thermodynamics states that heat transfer occurs spontaneously only from higher to lower temperature bodies.
  • The second law of thermodynamics deals with the direction taken by spontaneous processes.
  • The law that forbids these processes is called the second law of thermodynamics .
  • The already familiar direction of heat transfer from hot to cold is the basis of our first version of the second law of thermodynamics.
  • Contrast the concept of irreversibility between the First and Second Laws of Thermodynamics

• The Second Law of Thermodynamics

  • The second law of thermodynamics states that every energy transfer increases the entropy of the universe due to the loss of usable energy.
  • The second law of thermodynamics explains why: No energy transfers or transformations in the universe are completely efficient.
  • Thermodynamically, heat energy is defined as the energy transferred from one system to another that is not doing work.
  • Since all energy transfers result in the loss of some usable energy, the second law of thermodynamics states that every energy transfer or transformation increases the entropy of the universe.
  • Explain how living organisms can increase their order despite the second law of thermodynamics

• The Three Laws of Thermodynamics

  • The laws of thermodynamics define fundamental physical quantities (temperature, energy, and entropy) that characterize thermodynamic systems.
  • The first law of thermodynamics, also known as Law of Conservation of Energy, states that energy can neither be created nor destroyed; energy can only be transferred or changed from one form to another.
  • The second law of thermodynamics says that the entropy of any isolated system always increases.
  • A simple way to think of the second law of thermodynamics is that a room, if not cleaned and tidied, will invariably become more messy and disorderly with time - regardless of how careful one is to keep it clean.
  • The third law of thermodynamics states that the entropy of a system approaches a constant value as the temperature approaches absolute zero.

• Spontaneous and Nonspontaneous Processes

  • The sign convention of changes in free energy follows the general convention for thermodynamic measurements.
  • The laws of thermodynamics govern the direction of a spontaneous process, ensuring that if a sufficiently large number of individual interactions (like atoms colliding) are involved, then the direction will always be in the direction of increased entropy.
  • The second law of thermodynamics states that for any spontaneous process, the overall ΔS must be greater than or equal to zero; yet, spontaneous chemical reactions can result in a negative change in entropy.
  • This does not contradict the second law, however, since such a reaction must have a sufficiently large negative change in enthalpy (heat energy).
  • That is, the ΔS of the surroundings increases enough because of the exothermicity of the reaction so that it overcompensates for the negative ΔS of the system.

• Changes in Energy

  • The concept of entropy evolved in order to explain why some processes (permitted by conservation laws) occur spontaneously while their time reversals (also permitted by conservation laws) do not; systems tend to progress in the direction of increasing entropy.
  • This fact has several important consequences in science: first, it prohibits "perpetual motion" machines; and second, it implies the arrow of entropy has the same direction as the arrow of time.
  • In classical thermodynamics the entropy is interpreted as a state function of a thermodynamic system.
  • The entropy of the thermodynamic system is a measure of how far the equalization has progressed.
  • The second law of thermodynamics shows that in an isolated system internal portions at different temperatures will tend to adjust to a single uniform temperature and thus produce equilibrium.

• Heat Engines

  • In thermodynamics, a heat engine is a system that performs the conversion of heat or thermal energy to mechanical work.
  • The second law of thermodynamics (second expression) also states, with regard to using heat transfer to do work: It is impossible in any system for heat transfer from a reservoir to completely convert to work in a cyclical process in which the system returns to its initial state.
  • The second law, in its second form, clearly states that such engines cannot have perfect conversion of heat transfer into work done.
  • The first law of thermodynamics states that ΔU=Q−W, where Q is the net heat transfer during the cycle (Q=Qh−Qc) and W is the net work done by the system.
  • (a) Heat transfer occurs spontaneously from a hot object to a cold one, consistent with the second law of thermodynamics.

• A Review of the Zeroth Law

  • Zeroth law justifies the use of thermodynamic temperature, defined as the shared temperature of three designated systems at equilibrium.
  • This law was postulated in the 1930s, after the first and second laws of thermodynamics had been developed and named.
  • It is called the "zeroth" law because it comes logically before the first and second laws (discussed in Atoms on the 1st and 2nd laws).
  • A brief introduction to the zeroth and 1st laws of thermodynamics as well as PV diagrams for students.
  • Discuss how the Zeroth Law of Thermodynamics justifies the use of thermodynamic temperature

• The Zeroth Law of Thermodynamics

  • The Zeroth Law of Thermodynamics states that systems in thermal equilibrium are at the same temperature.
  • There are a few ways to state the Zeroth Law of Thermodynamics, but the simplest is as follows: systems that are in thermal equilibrium exist at the same temperature.
  • What the Zeroth Law of Thermodynamics means is that temperature is something worth measuring, because it indicates whether heat will move between objects.
  • However, according to the Zeroth Law of Thermodynamics, if the systems are in thermal equilibrium, no heat flow will take place.
  • There are more formal ways to state the Zeroth Law of Thermodynamics, which is commonly stated in the following manner:

• The First Law of Thermodynamics

  • The first law of thermodynamics states that energy can be transferred or transformed, but cannot be created or destroyed.
  • The first law of thermodynamics deals with the total amount of energy in the universe.
  • The law states that this total amount of energy is constant.
  • According to the first law of thermodynamics, energy can be transferred from place to place or changed between different forms, but it cannot be created or destroyed.
  • Another useful form of the first law of thermodynamics relates heat and work for the change in energy of the internal system:

• The First Law

  • The 1st law of thermodynamics states that internal energy change of a system equals net heat transfer minus net work done by the system.
  • The first law of thermodynamics is a version of the law of conservation of energy specialized for thermodynamic systems.
  • In equation form, the first law of thermodynamics is
  • The change in the internal energy of the system, ΔU, is related to heat and work by the first law of thermodynamics, ΔU=Q−W.
  • Explain how the net heat transferred and net work done in a system relate to the first law of thermodynamics