Some Key Definitions And Concepts

Before we dive into the Laws of Thermodynamics, there are some key definitions and concepts that we must understand. 

These are given below. 


  • System and Surroundings
In order to avoid confusion, scientists discuss thermodynamic values in reference to a system and its surroundings. Everything that is not a part of the system constitutes its surroundings. The system and surroundings are separated by a boundary. If matter is not able to pass across the boundary, then the system is said to be closed; otherwise, it is open.

For example, if the system is one mole of a gas in a container, then the boundary is simply the inner wall of the container itself. Everything outside of the boundary is considered the surroundings, which would include the container itself.




  • Thermodynamic States: 

The application of thermodynamic principles begins by defining a system that is in some sense distinct from its surroundings. 

For example, the system could be a sample of gas inside a cylinder with a movable piston, an entire steam engine, a marathon runner, the planet Earth, a neutron star, a black hole, or even the entire universe. 

A system’s condition at any given time is called its thermodynamic state. 

For a gas in a cylinder with a movable piston, the state of the system is identified by the temperature, pressure, and volume of the gas. These properties are characteristic parameters that have definite values at each state and are independent of the way in which the system arrived at that state. In other words, any change in value of a property depends only on the initial and final states of the system, not on the path followed by the system from one state to another. Such properties are called state functions. 

In contrast, the work done as the piston moves and the gas expands and the heat the gas absorbs from its surroundings depend on the detailed way in which the expansion occurs.


  • Thermodynamic Equilibrium
It is observed that some property of an object, like the pressure in a volume of gas, the length of a metal rod, or the electrical conductivity of a wire, can change when the object is heated or cooled. If two of these objects are brought into physical contact there is initially a change in the property of both objects. But, eventually, the change in property stops and the objects are said to be in thermal, or thermodynamic equilibrium.

  • Work and Energy
Energy is a measurement of the ability of something to do work. It is not a material substance. Energy can be stored and measured in many forms.
Energy is never really destroyed. It is just transferred from one form to another, doing work in the process.


  • Total Internal Energy

The sum of all the microscopic forms of energy is called the internal energy of a system and is denoted by U.

The internal energy of a gas, depends only on the state of the gas and not on any process. It is a state variable.


  • Kinetic Energy
The energy that a system possesses as a result of its motion relative to some reference frame is called kinetic energy (KE).


  • Potential Energy
The energy that a system possesses as a result of its elevation in a gravitational field is called potential energy (PE).


  • Heat 
Heat is defined as the form of energy that is transferred between two systems (or a system and its surroundings) by virtue of a temperature difference (Q).

The amount of heat transferred into, or from a gas also depends on the initial and final states and the process which produces the final state


  • Work
Energy can cross the boundary of a closed system in the form of heat or work. Therefore, if the energy crossing the boundary of a closed system is not heat, it must be work. Work is the energy transfer associated with a force acting through a distance (W).

In the observations of the work done on, or by a gas, it is found that the amount of work depends not only on the initial and final states of the gas but also on the process, or path which produces the final state. 

Comments

Post a Comment

Popular posts from this blog

Second Law of Thermodynamics

Image
What is the Second Law of Thermodynamics? The Second Law of Thermodynamics, also known as the Law of Increased Entropy, says that over time the state of disorganization or entropy in a system will always increase.  Over time, usable energy will eventually give way to unusable energy. While energy cannot be created or destroyed according to the First Law, it can change form a useful state to a less-useful state, like thermal energy (heat). For example, as you read this article, entropy is all around you. Cells within your body are dying and degrading, an employee or coworker is making a mistake, the floor is getting dusty, and the heat from your coffee is spreading out. Zoom out a little, and businesses are failing, crimes and revolutions are occurring, and relationships are ending. Zoom out a lot further, and we see the entire universe marching towards a collapse. The Discovery of Entropy The identification of entropy is attributed to Rudolf Clausius (1822–1888), a German mathematician
Read more

Zeroth Law of Thermodynamics

Image
What is the Zeroth Law of Thermodynamics? The zeroth law of thermodynamics states that if two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other. The physical meaning is expressed by Maxwell in the words: " All heat is of the same kind ". As an illustration, suppose we have three objects as shown on the slide. Object A and Object B are in physical contact and in thermal equilibrium. Object B is also in thermal equilibrium with Object C. There is initially no physical contact between Object A and Object C. But, if Object A and Object C are brought into contact, it is observed that they are in thermal equilibrium Background of the Zeroth Law The zeroth law was first formulated and labelled by R. H. Fowler in 1931.  As the name suggests, its value as a fundamental physical principle was recognized more than half a century after the formulation of the first and the second laws of thermodynamics. It was named the zeroth law si
Read more

What is Thermodynamics?

Image
Thermodynamics can be defined as the science of energy. Although everybody 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 thermodynamics stems from the Greek words therme (heat) and dynamis (power), which is most descriptive of the early efforts to convert heat into power. Metallurgy: A field with vast applications of the concepts of Thermodynamics Thermodynamics is commonly defined as a branch of physics which deals with the energy and work of a system. 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. There are three principal laws of thermodynamics (and an additional zeroth law). Each law leads to the definition of thermodynamic properties which help us to understand and predict the operation of a physical system.
Read more