Introduction

Excerpts

• Introduction

  If a perfect gas be allowed to expand, doing external work, and be prevented from cooling by connecting it with a heat-reservoir of higher temperature, the temperature of the gas, and at the same time its internal energy, remains unchanged, and it may be said that the amount of heat given out by the reservoir is completely changed into work without an exchange of energy taking place anywhere.

• Introduction

  Such a proposition cannot be proved *a priori*, neither does it amount to a definition, but it contains a definite assertion, to be stated precisely in each case, which may be verified by actual experiment.

• Introduction

  Not every change which is consistent with the principle of the conservation of energy satisfies also the additional conditions which the second law imposes upon the processes, which actually take place in nature. In other words, the principle of the conservation of energy does not suffice for a unique determination of natural processes.

• Introduction

  If, for instance, an exchange of heat by conduction takes place between two bodies of different temperature, the first law, or the principle of the conservation of energy, merely demands that the quantity of heat given out by the one body shall be equal to that taken up by the other. Whether the flow of heat, however, takes place from the colder to the hotter body, or *vice versâ*, cannot be answered by the energy principle alone.

• Introduction

  If a heavy liquid be initially at rest at different levels in two communicating tubes, then motion will set in, so as to equalize the levels, for the centre of gravity of the system is thereby lowered, and the potential energy diminished. Equilibrium exists when the centre of gravity is at its lowest, and therefore the potential energy at a minimum, *i.e.* when the liquid stands at the same level in both tubes.

• Introduction

  There is but one way of clearly showing the significance of the second law, and that is to base it on facts by formulating propositions which may be proved or disproved by experiment.

• Introduction

  A process which can in no way be completely reversed is termed *irreversible*, all other processes *reversible*. That a process may be irreversible, it is not sufficient that it cannot be directly reversed.

• Introduction

  Consequently, either all or none of these processes are irreversible. There is no third possibility. If those processes are not irreversible, the entire edifice of the second law will crumble.

• Introduction

  Since there exists in nature no process entirely free from friction or heat-conduction, all processes which actually take place in nature, if the second law be correct, are in reality irreversible; reversible processes form only an ideal limiting case.

Equations

• Introduction

  \ce{\{H2\} + $\tfrac{1}{2}$ \{O2\} - (H2O)} = 68,400~\Unit{cal.}

  Forming water from hydrogen and oxygen at constant pressure gives off 68,400 cal of heat, and decomposing water absorbs the same amount, so the reaction's heat effect is fixed at that value (the book's equation (50)).

Problems

No exercises in this chapter.