Duduli

The pressure, volume & Temperature of a gas corresponding to critical point are called critical constants & are known as critical pressure, critical volume & critical temperature.

The third law of thermodynamics states that the entropy of a system approaches a constant value as the temperature approaches absolute zero.

The relation among any three of thermodynamics variables is called equation of state. → Equation of state for one mole of ideal gas is                         PV=RT

Every system is made of atoms, ions or molecules. Energy is stored in atoms,ions and molecules in different forms as electronic energy, nuclear energy, potential energy, kinetic energy etc. “The total energy stored in a system under a given set of conditions is called it's internal energy or intrinsic energy, U”.

It is defined as the amount of heat required to raise the temperature of one mole of a gas through 1⁰C when it's pressure is kept constant.

It is defined as the amount of heat required to raise the temperature of one mole of a gas through 1⁰C when it's volume is kept constant.

It is that point on the isothermal for the critical temperature at which the change of state from the gaseous state to the liquid state takes place under constant values of critical pressure & critical volume.

It is defined as the square root of mean of the squares of velocities of individual molecules.

The specific heat of a substance is defined as the quantity of heat required to raise the temperature of unit mass of the substance through 1 degree.

The changes of phase which take place at constant temperature & pressure & in which heat is either absorbed or evolved during change of phase are called first order phase transitions. → In first order please transitions, the entropy & density (or volume) change.

Gas & vapour states are the two distant stages of the same continuous phenomenon. These two states have distinct boundary which is governed by a particular temperature called the critical temperature. Above the critical temperature the substance is in the gaseous state and below the critical temperature it is in the vapour state.

As we know, in Joule-Thomson porous plug experiment, if a gas at constant high pressure is forced through a porous plug to a region of constant low pressure, the temperature of escaping gas changes. This is called Joule-Thomson effect.

The probability that a molecule will make collision in one second from an instant is called collision probability.

The different layers of a non-equilibrium gas may have different velocities.In such a case, the layer moving faster will import momentum to the layer moving slower to bring about an equilibrium state. Thus, the transport of momentum gives rise to the phenomenon of viscosity. Viscosity is the phenomenon of transportation of momentum.

Second order phase transitions can be defined as the phenomenon that takes place with no change in entropy & volume at constant temperature & pressure. e.g  ★ Transition of a ferromagnetic material to a paramagnetic material at the curie point. ★ Order-disorder transitions in chemical compounds & alloys.

A thermos flask consists of a double walled glass bottle. The space in between the two bottles is evacuated and sealed. Walls are highly polished (i.e silvered) to avoid radiation of heat.The outer polished surface of A does not radiate heat. Even if a little quantity of heat is radiated by A, most of it is reflected back by the polished surface of B. The evacuation of the space in between A & B helps in the elimination of the loss of heat by conduction and convection. Similarly ice kept inside the flask will not melt for a long time because heat radiations from outside cannot enter the inside of the bottle.

According to Nernst, “ The heat capacities of all solids tend to zero as the absolute zero of temperature is approached and that the internal energies and entropies of all substances become equal there, approaching their common value asymptotically tending to zero ”.  Usually it is called as third law of thermodynamics.

When a metal becomes superconductor, its thermal conductivity decreases considerably and tends to zero approximately as the cube of the temperature.Superconducting state being a distinct phase of matter having characteristic electrical, magnetic, thermodynamic and other physical properties.Superconductors have zero electrical resistance.In a superconducting state the magnetic permeability is also zero and shows perfect diamagnetism.This phenomenon is known as Meissner effect.

Brownian motion was first observed in 1827  by brown, a botanist.The phenomenon of Brownian movement can be easily observed in a laboratory if a colloidal solution is examined under an ultramicroscope.The non-stop random and haphazard(badly organized) motion of the particles in a medium is called Brownian motion.

“It is impossible to extract heat from a single body & convert the whole of heat into work”.