Thermodynamics is a branch of physics which deals with the energy and work of a system. It was born in the 19th century as scientists were first discovering how to build and operate steam engines. Thermodynamics deals only with the large scale response of a system which we can observe and measure in experiments. Small scale gas interactions are described by the kinetic theory of gases. The methods compliment each other; some principles are more easily understood in terms of thermodynamics and some principles are more easily explained by kinetic theory.

Thermodynamic ialah satu cabang fizik yang berurusan dengan tenaga dan kerja sesuatu sistem. Ianya lahir dalam abad ke 19, apabila ahli sains pertama kali mengkaji caramana membina dan mengendalikan enjin wap. Thermodynamic hanya membincangkan tindak balas sistem pada skala besar(Macroscopic), dimana dapat di perhati dan membuat sukatan dalam experiments. Tindak balas pada skala kecil (microscopic) yang melibatkan saling tindakan antara gas dibincangkan melalui teori kinetik gas.

Kaedahnya saling melengkapi antara satu sama lain; sesetengah prisip lebih mudah difahami melaui thermodynamic dan sesetengah pronsip pula lebih mudah dafahami melalui Teori kinetik.

There are three principal laws of thermodynamics which are described on separate slides. Each law leads to the definition of thermodynamic properties which help us to understand and predict the operation of a physical system. We will present some simple examples of these laws and properties for a variety of physical systems, although we are most interested in thermodynamics in the study of propulsion systems and high speed flows. Fortunately, many of the classical examples of thermodynamics involve gas dynamics. Unfortunately, the numbering system for the three laws of thermodynamics is a bit confusing. We begin with the zeroth law.

The zeroth law of thermodynamics involves some simple definitions of thermodynamic equilibrium. Thermodynamic equilibrium leads to the large scale definition of temperature, as opposed to the small scale definition related to the kinetic energy of the molecules. The first law of thermodynamics relates the various forms of kinetic and potential energy in a system to the work which a system can perform and to the transfer of heat. This law is sometimes taken as the definition of internal energy, and introduces an additional state variable, enthalpy.

Terdapat 3 hukum asas thermodynamic.

The zeroth law of thermodynamics, melibatkan takrif mudah bagi thermodynamic equilibrium. Thermodynamic equilibrium menjurus ke arah takrif skala besar bagi suhu Sebagai mengimbangi takrif skala kecil berkaitan dengan tenaga kinetik molekul. Hukum Pertamathermodynamics menghubungkaitkan pelbagai bentuk tenaga kinetik dan tenaga keupayaan dalam sesuatu sistem dengan kerja yang boleh di lakukan oleh sistem tersebut dan juga dengan pemindahan haba. Hukum ini kadangkala di terima sebagaitakrif tenaga dalam dan memperkenalkan satu pembolehubah keadaan yang dipanggil enthalpy

The first law of thermodynamics allows for many possible states of a system to exist. But experience indicates that only certain states occur. This leads to the second law of thermodynamics and the definition of another state variable called entropy.

Hukum thermodynamics pertama membolehkan bagi banyak kemungkinan keadaan sesuatu sistem wujud. Tetapi pengalaman menunjukkan hanya keadaan tertentu sahaja berlaku. Ini membawa kepada hukum keduathermodynamics dan penakrifan pembolehubah keadaan lain dipangil entropy. The second law stipulates that the total entropy of a system plus its environment can not decrease; it can remain constant for a reversible process but must always increase for an irreversible process.

Hukum kedua pula memastikan jumlah entropy sesuatu sistem dan persekitaraannya tidak boleh bertambah: ianya boleh kekal tetap bagi proses yang boleh di balikan tetapi mesti sentiasa bertambah bagi proses yang tidak boleh di terbalikkan.