What is the third law of thermodynamics clearly? Justify ur answer.?

Question

THIRD LAW OF THERMODYNSMICS:The properties of substanses at ABSOLUTE ZEROtemperature.

Answer 1

he Third Law of Thermodynamics
The third law of thermodynamics is usually stated as a definition: the entropy of a perfect crystal of an element at the absolute zero of temperature is zero.

At the absolute zero of temperature, there is zero thermal energy or heat. Since heat is a measure of average molecular motion, zero thermal energy means that the average atom does not move at all. Since no atom can have less than zero motion, the motion of every individual atom must be zero when the average molecular motion is zero. When none of the atoms which make up a perfectly ordered crystal move at all, there can be no disorder or different states possible for the crystal.

Taking the entropy of a perfect crystal of an element to be zero at the absolute zero of temperature establishes a method by which entropies of elements at any higher temperature can be determined. Since by definition dS = qrev/T, the mathematical integral of dS from zero to any higher temperature T is the integral, over that temperature range, of qrev/T. In other words. the difference S - S0 is the integral from zero to a temperature T of (Cp/T)dT. The molar heat capacity at any temperature is a measurable quantity, and so this difference can be determined experimentally.

The third law of thermodynamics is simply the statement that S0 is zero by definition for a pure element, and so if the heat capacity is measured under conditions of reversible heat flow, as it can be, and as a function of temperature at low temperatures, as it can be, then the entropy Sof a pure element at any temperature T is given by:

S = the integral from zero to T of (Cp/T)dT

The values we usually write as S0, the standard entropy of a substance, are actually the integral from zero to the standard temperature, 298.15 K, of (Cp/T)dT in order that the values of standard entropies of substances can be used with standard values for other thermodynamic functions such as enthalpy and free energy.

The value of the entropy of an element at any temperature, including 298.15 K which is the temperature of the standard entropy S0, can be obtained from careful measurements of the heat capacity of the element from the desired temperature down to absolute zero. Experimentally, chemists have been unable to reach the absolute zero of temperature, but measurements can be and have been made down to within 0.1 K of it and the heat capacity below measurable range can be accurately estimated. The entropy of the element is obtained from integration of the heat capacity measurements. If the crystal changes form, or melts, within the temperature range desired, then the entropy of that change must also be measured and included.

The entropies of compounds can be determined from thermodynamic measurements made on the reactions which form them from the elements or dissociate them to their constituent elements once the entropies of the elements themselves are established. The values of standard entropies of elements and compounds at 25oC given in the tables of the thermodynamic properties of pure substances are all based upon the third law of thermodynamics.

Answer 2

3rd Law Of Thermodynamics Definition

Answer 3

The entropy of a crystalline substance tends to zero as it approaches absolute zero of temperature.

This is sometimes called the Nernst Heat Theorem.

I don't have to justify it - ask Mr Nernst!!

Answer 4

In school the teacher put it this way; A system tried to achieve maximum dissipation and minimum energy level
.
In atoms the minimum energy level is its mass structure.
This is what hapens at the absolute zero.

Answer 5

i think pranesh is going too long and far
in simple layman's language third law is at absolute zero Kelvin
temperature disorder [in sci terms entropy] in substances
is nil
this is because this is the lowest attainable temperature and at this temperature molecules become completely inactive
and attain orderly arrangement.