The study of heat and heat-related phenomena, based on four fundamental laws.
Zeroth Law If two systems are in thermodynamic equilibrium with a third, they will be in thermodynamic equilibrium with one another. For example, two objects left to stand a while in a still room will be the same temperature as the room and therefore as each other.
First Law The sum of the energy changes occurring in some isolated process is zero, which is equivalent to the statement that total energy is conserved. For example, a battery may be used to raise the temperature of some water electrically, in which case chemical energy from the battery is converted into heat; but the total energy of the complete system before and after the circuit is switched on is the same.
Second Law A law giving direction to thermodynamic processes in time, and thus forbidding some which would otherwise be allowed by the First Law. It may be expressed in several equivalent ways. 1 No heat engine can have a thermal efficiency of 100%, ie it is impossible to convert heat totally into mechanical work; for example, car engines and power stations can never be 100% efficient, no matter how well they are built. 2 No process may have as its only outcome the transfer of heat from a cold object to a hot one; for example, a refrigerator requires power to make an object at room temperature cold, whereas a cold object will warm up to room temperature on its own. 3 A system will always finish in the state which can be realized in the greatest number of ways; for example, a drop of ink in water will finish up dispersed evenly through the water since this corresponds to the greatest number of arrangements of ink and water atoms. 4 For a closed system, entropy is either constant or increasing.
Third Law Absolute zero can never be reached.
Before the 19th-c, it was generally assumed that heat was a material substance, termed caloric. Hot objects were thought to contain more caloric than cold ones, and an object's supply of caloric was limited. The modern conception, that heat is a form of energy, and that heat flow is energy transfer, was originally due to Count Rumford in 1798. Conservation of energy was first understood by Sadi Carnot in 1830, James Joule in 1843, and others. Joule used a system of falling weights to drive paddles immersed in water, thereby raising its temperature and establishing the equivalence of mechanical energy and heat (1845). The idea that all forms of energy are equivalent comes from Hermann von Helmholtz. Lord Kelvin proposed the absolute thermodynamic temperature scale (1845), which now bears his name. The second law of thermodynamics is due to him (1851) and Rudolf Clausius (1850). Kelvin developed the notion that mechanical energy gradually dissipates into heat energy, an idea developed by Clausius into the concept of entropy. Classical thermodynamics, which is independent of the microscopic detail of systems, stems largely from their work. Expressing the thermodynamic properties of systems on the assumption that they are composed of large numbers of distinct atoms is termed statistical mechanics.
Thermodynamics (from the Greek thermos meaning heat and dynamics meaning power) is a branch of physics that studies the effects of changes in temperature, pressure, and volume on physical systems at the macroscopic scale by analyzing the collective motion of their particles using statistics. thus, in essence thermodynamics studies the movement of energy and how energy instills movement.
The starting point for most thermodynamic considerations are the laws of thermodynamics, which postulate that energy can be exchanged between physical systems as heat or work. They also postulate the existence of a quantity named entropy, which can be defined for any system. A system is composed of particles, whose average motions define its properties, which in turn are related to one another through equations of state. Properties can be combined to express internal energy and thermodynamic potentials, which are useful for determining conditions for equilibrium and spontaneous processes.
With these tools, thermodynamics describes how systems respond to changes in their surroundings.
History
A short history of thermodynamics begins with the German scientist Otto von Guericke who in 1650 built and designed the world's first vacuum pump and created the world's first ever vacuum (known as the Magdeburg hemispheres).
Classical thermodynamics
Classical thermodynamics is the original early 1800s variation of thermodynamics concerned with thermodynamic states, and properties as energy, work, and heat, and with the laws of thermodynamics, all lacking an atomic interpretation. In precursory form, classical thermodynamics derives from physicist Robert Boyle’s 1662 postulate that the pressure P of a given quantity of gas varies inversely as its volume V at constant temperature;
Statistical thermodynamics
With the development of atomic and molecular theories in the late 19th century, thermodynamics was given a molecular interpretation. This field is called statistical thermodynamics, which can be thought of as a bridge between macroscopic and microscopic properties of systems. Essentially, statistical thermodynamics is an approach to thermodynamics situated upon statistical mechanics, which focuses on the derivation of macroscopic results from first principles. The statistical approach is to derive all macroscopic properties (temperature, volume, pressure, energy, entropy, etc.) from the properties of moving constituent particles and the interactions between them (including quantum phenomena).
Chemical thermodynamics
Chemical thermodynamics is the study of the interrelation of heat with chemical reactions or with a physical change of state within the confines of the laws of thermodynamics. During the years 1873-76 the American mathematical physicist Willard Gibbs published a series of three papers, the most famous being On the Equilibrium of Heterogeneous Substances, in which he showed how thermodynamic processes could be graphically analyzed, by studying the energy, entropy, volume, temperature and pressure of the thermodynamic system, in such a manner to determine if a process would occur spontaneously.
Thermodynamic systems
An important concept in thermodynamics is the “system”. A system is the region of the universe under study. A system is separated from the remainder of the universe by a boundary which may be imaginary or not, but which by convention delimits a finite volume. The possible exchanges of work, heat, or matter between the system and the surroundings take place across this boundary. There are five dominant classes of systems:
Isolated Systems – matter and energy may not cross the boundary.
For isolated systems, as time goes by, internal differences in the system tend to even out; A system in which all equalizing processes have gone practically to completion, is considered to be in a state of thermodynamic equilibrium.
In thermodynamic equilibrium, a system's properties are, by definition, unchanging in time. Systems in equilibrium are much simpler and easier to understand than systems which are not in equilibrium. Often, when analyzing a thermodynamic process, it can be assumed that each intermediate state in the process is at equilibrium. Thermodynamic processes which develop so slowly as to allow each intermediate step to be an equilibrium state are said to be reversible processes.
Thermodynamic parameters
The central concept of thermodynamics is that of energy, the ability to do work. As stipulated by the first law, the total energy of the system and its surroundings is conserved. For comparison, in mechanics, energy transfer results from a force which causes displacement, the product of the two being the amount of energy transferred. In a similar way, thermodynamic systems can be thought of as transferring energy as the result of a generalized force causing a generalized displacement, with the product of the two being the amount of energy transferred.
Thermodynamic instruments
There are two types of thermodynamic instruments, the meter and the reservoir. A thermodynamic meter is any device which measures any parameter of a thermodynamic system. A calorimeter is a device which is used to measure and define the internal energy of a system.
A thermodynamic reservoir is a system which is so large that it does not appreciably alter its state parameters when brought into contact with the test system. It is used to impose a particular value of a state parameter upon the system. For example, a pressure reservoir is a system at a particular pressure, which imposes that pressure upon any test system that it is mechanically connected to. If, for example, a thermometer, were to act as a temperature reservoir it would alter the temperature of the system being measured, and the reading would be incorrect. Ideal meters have no effect on the state variables of the system they are measuring.
Thermodynamic states
When a system is at equilibrium under a given set of conditions, it is said to be in a definite state. The state of the system can be described by a number of intensive variables and extensive variables. The properties of the system can be described by an equation of state which specifies the relationship between these variables. State may be thought of as the instantaneous quantitative description of a system with a set number of variables held constant.
Thermodynamic processes
A thermodynamic process may be defined as the energetic evolution of a thermodynamic system proceeding from an initial state to a final state. Typically, each thermodynamic process is distinguished from other processes, in energetic character, according to what parameters, as temperature, pressure, or volume, etc., are held fixed. The six most common thermodynamic processes are shown below:
An isobaric process occurs at constant pressure.The laws of thermodynamics
In thermodynamics, there are four laws of very general validity, and as such they do not depend on the details of the interactions or the systems being studied. Hence, they can be applied to systems about which one knows nothing other than the balance of energy and matter transfer.
The four laws are:
Zeroth law of thermodynamics, stating that thermodynamic equilibrium is an equivalence relation. If two thermodynamic systems are separately in thermal equilibrium with a third, they are also in thermal equilibrium with each other. First law of thermodynamics, about the conservation of energy The change in the internal energy of a closed thermodynamic system is equal to the sum of the amount of heat energy supplied to the system and the work done on the system. Second law of thermodynamics, about entropy The total entropy of any isolated thermodynamic system tends to increase over time, approaching a maximum value. Third law of thermodynamics, about absolute zero temperature As a system asymptotically approaches absolute zero of temperature all processes virtually cease and the entropy of the system asymptotically approaches a minimum value;Thermodynamic potentials
As can be derived from the energy balance equation on a thermodynamic system there exist energetic quantities called thermodynamic potentials, being the quantitative measure of the stored energy in the system. The four most well known potentials are:
| Internal energy | |
| Helmholtz free energy | |
| Enthalpy | |
| Gibbs free energy |
Potentials are used to measure energy changes in systems as they evolve from an initial state to a final state. The potential used depends on the constraints of the system, such as constant temperature or pressure. Internal energy is the internal energy of the system, enthalpy is the internal energy of the system plus the energy related to pressure-volume work, and Helmholtz and Gibbs free energy are the energies available in a system to do useful work when the temperature and volume or the pressure and temperature are fixed, respectively.
Related branches
| Atmospheric thermodynamics Biological thermodynamics Black hole thermodynamics Chemical thermodynamics Classical thermodynamics Equilibrium thermodynamics | Non-equilibrium thermodynamics Phenomenological thermodynamics Psychodynamics Quantum thermodynamics Statistical thermodynamics Thermoeconomics |
Lists and timelines
History of thermodynamics List of important publications in thermodynamics List of notable textbooks in statistical mechanics Timeline of thermodynamics, statistical mechanics, and random processes Parmenides' influence on the development of thermodynamicsOther
| Calorimetry Debye-Hückel equation Fluid dynamics Legendre transformation Onsager reciprocal relations Phase equilibrium | Philosophy of thermal and statistical physics Statistical mechanics Thermal analysis Thermodynamic equations Thermodynamic properties Thermodynamic databases for pure substances |
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