Thermodynamics is a central branch in physics and chemistry. The concepts & principles of the subject investigate the phenomena of work & energy, primarily in macroscopic systems. Thermodynamics is critical in almost every kind of engineering & mechanical system. From rocket science to steel plants, internal combustion engines, cooling systems, and the International Space Station, thermodynamics occurs everywhere.
Homework help experts from Tophomeworkhelper.com, one of the USA’s largest academic service providers, present a concise overview of the rudimentary concepts & laws in thermodynamics in this article. Read on for some quick revision.
The Fundamental Concepts of Thermodynamics
Thermodynamics is the study of the flow or movement of heat & energy in a system and the effect of work on the flow of energy. The study of thermodynamics looks primarily into the flow of heat/energy and the work done on a large or grander scale. Thus, thermodynamics concerns itself with energy & workflow in macroscopic systems. Such systems are composed of a large number (say, N >>>1) of fundamental particles (atoms, molecules, ions, etc.).
Thermodynamic systems can be open, closed, isolated, non-isolated, movable, or rigid. Open systems can exchange matter with their surroundings, unlike closed systems that cannot. Isolated systems can’t exchange energy with their surroundings, while non-isolated systems can. It should be intuitive that open systems cannot be isolated.
Systems can be in thermodynamic equilibrium if the system has no flux, flow, or macroscopic movement.
Thermodynamic analysis of any system involves closely examining some key system variables. The changes in these thermodynamic variables dictate or characterize a system’s thermodynamic state, and their quantities/values depend only on the initial and final state of the system. Also known as state variables, they are the opposite of path variables, whose quantities depend on the path a system takes as it changes from one state to another.
Key thermodynamic variables are à
- Internal Energy (U)
This state variable denotes the energy contained within any system (latent, chemical bond, nuclear energy, etc.) There are still no clearly defined ways to measure or quantify the internal energy of any system. We instead focus on the change in the internal energy of a system rather than on absolute values.
- Enthalpy (H)
The enthalpy of a system is a state variable that defines the sum of its internal energy & the product of pressure & volume, i.e., the work done on or by a system. Enthalpy of a system is measured under constant pressure and is equivalent to the heat released or absorbed due to changes in the internal energy and the work done by or on a constant-pressure system. The variable depends entirely on a system’s temperature, pressure, and volume.
The expression for enthalpy is as follows à: H = U + PV, where U is the internal energy, P is pressure & V is volume.
- Entropy (S)
Entropy has many definitions, chief amongst which is the disorder in a system. The higher the entropy of a system, the more chaotic it is. Entropy also represents the number of states a system can go through or achieve.
Entropy is expressed via the following relation: à dS = dQ/T, that is, the ratio of the change in heat energy and the temperature of a system.
- Free Energy or Gibb’s Free Energy (G)
The free energy in a system is the difference between the enthalpy and the product of entropy & temperature. Also called Gibb’s free energy, it establishes a relationship between entropy & enthalpy. It is a state function and is expressed using the following expression à
dG = dH – d(TS)
where H is the enthalpy of a system, T is the temperature, and S is the entropy or intrinsic disorder in a system.
- Heat Energy (Q)
Unlike enthalpy, entropy, internal, or free energy, a system’s heat energy absorbed or released is a path variable. The heat produced or acquired during a process depends on the path the system takes to reach a particular state during a process. Q is positive if heat energy is added to the system and negative if heat is released.
- Work (W)
Work done in thermodynamic systems is generally expressed as the product of pressure & volume. This relation stems from the general gas laws, namely, Boyle’s, Charle’s, and Avogadro’s, which come together to form the ideal gas law. The same relationship can be extended to an ideal thermodynamic system.
The expression for work done by or on an ideal thermodynamic system is à
PV = nRT
The work done by a thermodynamic system generally results in a change in the state of a system.
As we draw things close, let’s look at the three central laws of thermodynamics.
The Laws of Thermodynamics
There are three specific laws governing thermodynamics. Each of these laws defines certain thermodynamic properties that aid in understanding a thermodynamic system.
- The Zeroth Law: It defines conditions of thermodynamic equilibrium. The law states that the two systems in thermodynamic equilibrium should be at the same temperature.
- The First Law: The first law defines a system’s internal energy (U) and states that it is equal to the difference between the heat (released or absorbed) and the work done on or by a system.
- The Second Law: This is the entropy law, which states that the entropy of a reversible process remains the same for a system. In contrast, the entropy of a system increases when it undergoes an irreversible process. The second law equates change in the entropy of a system with the ratio between the change in heat energy in that system and the system’s temperature.
