10.2 Second Law of Thermodynamics

10.2 Second Law of Thermodynamics

  • There are many phenomena that are not forbidden by the first law of thermodynamics.
    • When an object falls from a table to the ground, its potential energy is first converted into heat, and then it comes to rest on the ground.
    • The reverse process, whereby the heat from the floor would enter the object and be converted into energy, can be done.
    • This event doesn't happen.
    • Certain types of events are irreversible.
    • The broken objects don't mend on their own.
    • The spilled water doesn't get back into a container.
    • The irreversibility of these types of events is connected to the behavior of the systems.
  • Three coins are arranged on a tray.
    • This will be considered an ordered arrangement.
    • If we shake the tray so that each coin has an equal chance of landing on the tray with either head or tail up, then we would have a fair chance of landing on the tray.
    • The table shows the possible arrangements of coins.
    • There are eight possible outcomes of tossing the coins.
    • The original ordered arrangement of three heads is only yielded by one of these.
    • We must toss the coins eight times before we can see the three-head arrangement again.
  • The probability of returning to the ordered arrangement of all heads decreases as the number of coins increases.
  • The probability of getting all heads is very small with 1000 coins.
    • We could shake the tray and not see it again.
    • The number of possible coin arrangements is large, and only one of them is the ordered arrangement; therefore, although any one of the coin arrangements--including the ordered one--is equally likely, the probability of returning to an The probability of returning to an ordered arrangement decreases as the number of coins increases.
    • If we disturb an ordered arrangement, it is likely to become disorganized.
    • All events that involve a collective behavior of many components are characteristic of this type of behavior.
  • The type of behavior shown in the coin experiment is illustrated by the second law of thermodynamics.
    • The implication of this statement is seen to be enormous once the universal applicability of the second law is recognized.
    • The limitations on information transmission, the meaning of time sequence, and the fate of the universe can be deduced from the second law.
    • These subjects are not part of our discussion.
  • The limitation on the con version of heat and internal energy is an important implication of the second law.
    • The restriction can be understood by looking at the difference between heat and other forms of energy.
  • We defined heat as the transfer of energy from a hotter body to a cooler one.
    • When we looked at the details of the energy transfer, we saw that it could be attributed to a specific type of energy.
    • It may not be obvious why the concept of heat is necessary.
    • We would have to deal with each type of energy transfer separately if we wanted to develop a theory of thermodynamics without using the concept of heat explicitly.
    • Keeping track of each of the different ways energy is being transferred to or from a body is not usually necessary.
    • The effect of energy is the same regardless of how it enters the body.
    • The internal energy of the body is raised.
    • The concept of heat energy is useful.
  • The random nature of heat's manifestations distinguishes it from other forms of energy.
  • Random chaotic motion of atoms is the form of internal energy.
    • The propagating waves travel in random directions when heat is transferred.
    • The phases of the wave along the wave front are random as the radiation is emitted over a wide wavelength.
    • Other forms of energy are ordered.
    • Specific arrangements of atoms in a molecule are how chemical energy is present.
    • There is a well-defined position of an object.
  • Because of its random nature, heat energy cannot be completely converted to other forms of energy.
    • The behavior of a gas will be used to illustrate our discussion.
    • Let's look at how heat is converted to work in a heat engine.
  • The internal energy of the gas is raised by the increase in the heat flow into the gas.
    • The molecule moving in the direction of the piston collides with the one on the other side.
    • Internal energy is used to convert heat into work.
  • The heat added to the gas causes the molecule in the cylinder to move in random directions, but only the molecule that moves in the direction of the piston can exert a force on it.
    • The molecule that moves toward the piston can be converted into work.
    • The added heat would have to be converted into work in order for the gas molecule to move.
    • This is very unlikely in a large group of molecules.
  • A group of monkeys who are hitting typewriter keys at random and who by chance type out the complete works of Shakespeare without error are the odds against the complete conversion of 1 cal of heat into work.