THERMODYNAMICS AND ENERGY

Thermodynamics can be defined as the science of

has a feeling of what energy is, it is difficult to give a precise definition

for it. Energy can be viewed as the ability to cause changes.

The name

energy. Although everybodythermodynamics stems from the Greek words therme (heat) and

dynamis

heat into power. Today the same name is broadly interpreted to include all

aspects of energy and energy transformations, including power generation,

refrigeration, and relationships among the properties of matter.

One of the most fundamental laws of nature is the

principle.

one form to another but the total amount of energy remains constant. That is,

energy cannot be created or destroyed. A rock falling off a cliff, for example,

picks up speed as a result of its potential energy being converted to kinetic

energy (Fig. 1–1). The conservation of energy principle also forms the backbone

of the diet industry: A person who has a greater energy input (food)

than energy output (exercise) will gain weight (store energy in the form of

fat), and a person who has a smaller energy input than output will lose

weight (Fig. 1–2). The change in the energy content of a body or any other

system is equal to the difference between the energy input and the energy

output, and the energy balance is expressed as

The

of energy principle, and it asserts that

property. The

(power), which is most descriptive of the early efforts to convertconservation of energyIt simply states that during an interaction, energy can change fromEin
Eout E.first law of thermodynamics is simply an expression of the conservationenergy is a thermodynamicsecond law of thermodynamics asserts that energy has quality

as well as

decreasing quality of energy. For example, a cup of hot coffee left on a table

eventually cools, but a cup of cool coffee in the same room never gets hot

by itself (Fig. 1–3). The high-temperature energy of the coffee is degraded

(transformed into a less useful form at a lower temperature) once it is transferred

to the surrounding air.

Although the principles of thermodynamics have been in existence since

the creation of the universe, thermodynamics did not emerge as a science

until the construction of the first successful atmospheric steam engines in

England by Thomas Savery in 1697 and Thomas Newcomen in 1712. These

engines were very slow and inefficient, but they opened the way for the

development of a new science.

The first and second laws of thermodynamics emerged simultaneously in

the 1850s, primarily out of the works of William Rankine, Rudolph Clausius,

and Lord Kelvin (formerly William Thomson). The term

quantity, and actual processes occur in the direction ofthermodynamics

was first used in a publication by Lord Kelvin in 1849. The first

thermodynamic textbook was written in 1859 by William Rankine, a professor

at the University of Glasgow.

It is well-known that a substance consists of a large number of particles

called

behavior of these particles. For example, the pressure of a gas in a container

is the result of momentum transfer between the molecules and the walls of

the container. However, one does not need to know the behavior of the gas

molecules. The properties of the substance naturally depend on the

particles to determine the pressure in the container. It would be sufficient to

attach a pressure gage to the container. This macroscopic approach to the

study of thermodynamics that does not require a knowledge of the behavior

of individual particles is called

direct and easy way to the solution of engineering problems. A more elaborate

approach, based on the average behavior of large groups of individual

particles, is called

is rather involved and is used in this text only in the supporting role.

classical thermodynamics. It provides astatistical thermodynamics. This microscopic approach