Thermodynamics

This topic focuses on energy work of a system but it can only deal with a large scale response to heat in a system. Thermodynamics is the study of the work, heat and energy of a system. The smaller scale gas interactions can be explained using the kinetic theory of gases. Thermodynamics focuses on how a heat transfer is related to various energy changes within a physical system undergoing a thermodynamic process. These usually result in work being done by the system and are guided by the laws of thermodynamics. They are the zeroth law, the first law, and the second law. These laws help us understand predict the the operation of the physical system. In order to understand the laws, you must first understand thermal equilibrium. Thermal equilibrium is reached when a object that is at a higher temperature is in contact with an object that is at a lower temperature and the first object transfers heat to the latter object until they approach the same temperature and maintain that temperature constantly. It is also important to note that any thermodynamic system in thermal equilibrium possesses internal energy.

Zeroth Law

The zeroth law states that if two systems are at thermal equilibrium at the same time as a third system, then all of the systems are at equilibrium with each other. If systems A and C are in thermal equilibrium with B, then system A and C are also in thermal equilibrium with each other. There are underlying ideas of heat that are also important. The most prominent one is that all heat is of the same kind. As long as the systems are at thermal equilibrium, every unit of internal energy that passes from one system to the other is balanced by the same amount of energy passing back. This also applies when the two systems or objects have different atomic masses or material.

A Mathematical Model

If A = B and A = C, then B = C A = B = C

First Law

The first law of thermodynamics defines the internal energy (E) as equal to the difference between heat transfer (Q) into a system and work (W) done by the system. It simply states that energy can neither be created nor destroyed. Heat removed from a system would be given a negative sign and heat applied to the system would be given a positive sign. Internal energy can be converted into other types of energy because it acts like potential energy. Heat and work, however, cannot be stored or conserved independently because they depend on the process. This allows for many different possible states of a system to exist. There can be a process known as the adiabatic process in which there is no heat transfer. This occurs when a system is full insulated from the outside environment. The implementation of this law also brings about another useful state variable, enthalpy.

A Mathematical Model

E2 - E1 = Q - W

Second Law

The second law states that there is another useful variable of heat, entropy (S). Entropy can be described as the disorder or chaos of a system, but in physics, we will just refer to it as another variable like enthalpy or temperature. For any given physical process, the combined entropy of a system and the environment remains a constant if the process can be reversed. The second law also states that if the physical process is irreversible, the combined entropy of the system and the environment must increase. Therefore, the final entropy must be greater than the initial entropy.

Mathematical Models

[math]\displaystyle{ \Delta S = \Delta Q/T }[/math]
[math]\displaystyle{ S_f = S_i }[/math] (reversible process)
[math]\displaystyle{ S_f \gt S_i }[/math] (irreversible process)

Examples

First Law

A pendulum swings back and forth gradually slows down until it comes to rest because of friction. Due to friction, there is a small but steady transfer of heat energy from the system (pendulum) to the surroundings (the environment around the pendulum). Due to the first law of thermodynamics, the energy of the system must decrease as heat is lost to the surroundings.

Second Law

Reversible process: Ideally forcing a flow through a constricted pipe, where there are no boundary layers. As the flow moves through the constriction, the pressure, volume and temperature change, but they return to their normal values once they hit the downstream. This return to the variables' original values allows there to be no change in entropy. It is often known as an isentropic process.

Irreversible process: When a hot object and cold object are put in contact with each other, eventually the heat from the hot object will transfer to the cold object and the two will reach the same temperature and stay constant at that temperature, reaching equilibrium. However, once those objects are separated, they will remain at that equilibrium temperature until something else acts upon it. The objects do not go back to their original temperatures so there is a change in entropy.

Computational Model

http://jersey.uoregon.edu/vlab/Thermodynamics/

This virtual experiment gives you visual representation of thermal equilibrium and how it is reached when beginning with different initial conditions.

Connectedness

This topic is something I am interested in because, as a mechanical engineering major, I would like to go into either sustainable energy or urban development. Both of which must deal with and contain heat transfer that goes on in the systems. With sustainable energy, many processes include the heating up of renewable resources like water or nuclear power plants. These resources must be heated up to very high temperatures and therefore must be contained to avoid harm to any person or thing.

History

Thermodynamics was brought up as a science in the 18th and 19th centuries. However, it was first brought up by Galilei, who introduced the concept of temperature and invented the first thermometer. G. Black first introduced the word 'thermodynamics'. Later, G. Wilke introduced another unit of measurement known as the calorie that measures heat. The idea of thermodynamics was brought up by Nicolas Leonard Sadi Carnot. He is often known as "the father of thermodynamics". It all began with the development of the steam engine during the Industrial Revolution. He devised an ideal cycle of operation. During his observations and experimentations, he had the incorrect notion that heat is conserved, however he was able to lay down theorems that led to the development of thermodynamics. In the 20th century, the science of thermodynamics became a conventional term and a basic division of physics. Thermodynamics dealt with the study of general properties of physical systems under equilibrium and the conditions necessary to obtain equilibrium.

Thermodynamics

Contents

Thermodynamics

Zeroth Law

A Mathematical Model

First Law

A Mathematical Model

Second Law

Mathematical Models

Examples

First Law

Second Law

Computational Model

Connectedness

History

See also

Further reading

External links

References

Navigation menu