Thermodynamics, Physics tutorial


Thermodynamics is an area of science which comprises relationship between heat and other types of energy. Thermodynamics was found and studied beginning in 1800s. At that time, it was linked to and gained significance due to the use of steam engines.

Thermodynamics can be broken down in four laws. Though added to laws of thermodynamics after other three laws, zeroth law is generally discussed first. It defines that if two systems are in thermal equilibrium with the third system, then they are in thermal equilibrium with each other. In other words, if two systems are same temperature as the third system, then all three are same temperatures.

First law of thermodynamics: It states that total energy of the system remains constant, even if it is converted from one form to another. For instance, kinetic energy -energy that the object possesses when it moves - is converted to heat energy when the driver presses brakes on the car to slow it down. There are frequently catch phrases to assist people remember first law of thermodynamics: Work is heat, and heat is work. Mainly, work and heat are equal.

Second law of thermodynamics: It is one of the most essential laws in science. It defines that heat can't flow to the system at higher temperature from a system at a lower temperature by its own volition. For such action to happen, work should be done. If the ice cube is placed in the cup of warm water, the ice cube melts as heat from water flows into it. End result is the cup of water which is slightly cooler. Ice cubes can only form if energy is utilized.

Another example of second law only working with addition of energy can be observed with older refrigerator. In that case, cooling of inside of the refrigerator warms outside of it. So, work is done and work makes heat. Work is completed by pump of refrigerator.

Second law of thermodynamics also says that things can exhaust. For example, if the brick house is left uncared for, it will ultimately crumble from wind, rain, cold, and other weather conditions. Though, if a pile of bricks if left unattended, it will never form the house, unless work is added to mix.

Third law of thermodynamics: It defines that change in entropy of the system when it converts from one form to another gets close to zero as its temperature nears zero on Kelvin scale. Zero on Kelvin scale is absolute lower limit to temperature - when atoms and molecules have least possible energy. Entropy is stated as availability of the system's energy to do work. So, it follows that there is absolute scale of entropy. As a result, no real system can ever reach zero degrees on Kelvin scale.

Thermodynamic Properties/Coordinates:

These are macroscopic coordinates or properties utilized to explain or characterize the system. As they are macroscopic properties or coordinates, they can be seen and estimated. Some examples are Temperature (T), thermal conductivity ( k ), Volume (V), specific heat capacity at constant pressure (CP ), Pressure (P), density (Ρ), mass (m), specific heat capacity at constant volume (CV ), thermal diffusivity (α), and chemical potential (μ).

Thermodynamic System:

This is a system which could be explained in terms of thermodynamic coordinates or properties. Thermodynamic Systems can be categorized into followings depending on kind of boundary:

Open System: This is a system that its boundary permits transfer of mass and energy into or out of system. In other words, boundary permits exchange of mass and energy between system and surrounding.

Closed System: This is a system that its boundary lets exchange of energy alone (inform of heat) between system and its surrounding (i.e. boundary lets exchange of energy alone). This kind of boundary which lets exchange of heat is known as diathermal boundary.

Isolated System: This is a system that its boundary lets neither mass nor energy between it and surrounding. In other words, boundary doesn't permit exchange of mass nor energy.

Thermodynamic Processes:

There are numerous specific kinds of thermodynamic processes which take place often enough (and in practical situations) that they are generally treated in study of thermodynamics. Each has unique feature which identifies it, and that is helpful in examining energy and work change related to process.

Adiabatic process: This is the thermodynamic procedure in which there is no heat transfer into or out of system. For this procedure, change in quantity of heat is zero (i.e. ΔQ = 0 during this process)

Reversible Process: The reversible process can be stated as one which direction can be reversed by the infinitesimal change in some properties of system.

Quasi-static Process: This is a process which is performed in such a way that at every instant, system departs only infinitesimal from equilibrium state (i.e. almost static). Therefore quasi-static process closely approximates the succession of equilibrium states.

Non-quasi-static Process: This is a process which is performed in such a way that at every moment, there is finite departure of the system from the equilibrium state.

Extensive property:

The extensive property of the system depends on total amount of material in system. These are given below:

Mass: This provides the idea of how much of initial matter was contained in system and how much is left after procedure is complete.

Volume: This provides the idea of dimension of matter contained in and what will be the final dimension after the procedure is over.

Free energy: It is the energy in physical system that can be converted in work.

Entropy: It is the thermodynamic property that is utilized to find out energy available for useful work in a thermodynamic process.

Intensive property:

The intensive property is stated as the property that is independent of amount of material in system. These are given below:

Density: Density of the material is stated as the ratio between its volume and matter contained in or mass.

Molar property: Molar property primarily comprises detailing of molar volume, molar heat capacity, molar energy, molar entropy, and all these are quantified from point of moles of substance involved in.

Surface tension: It is the property of the liquid surface that helps in resisting any type of external force applied on it.

Viscosity: It is the measurable internal quantity of the fluid that resists its flow.

Thermal conductivity: Thermal conductivity (λ) is an intrinsic property of the material that relates its ability to perform heat.

Refractive index: Measure of speed of light in the medium is referred as refractive index of that medium.

Pressure: It is perpendicular force acting per unit area on surface of an object.

Temperature: It is the property of the matter that quantitatively states coldness or hotness of substance.

Thermodynamic Properties of Water:

Water has the second highest value of specific heat that is attributed to hydrogen bonding. Water exists in three states at the reasonably convenient temperature range. When it changes from solid to liquid states it takes heat from surroundings and when heat is supplied it changes from liquid to vapor. Ice to water (liquid) has different specific heat from liquid to gas. Latent heat of fusion is enthalpy which gets used to break crystal bonding. Latent heat of vaporization is enthalpy utilized to break hydrogen bonding.

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