And why do we use joules/Kelvin for defining entropy?

Answer 1

The inequality defining the Second Law of Thermodynamics sets entropy as the integral with respect to heat transfer over temperature. Heat transfer has units of Joules (or Btu in the english system) and absolute temperature has units of Kelvin (or degrees Rankine in the english system).

This makes the units for entropy J/K or Btu/deg R. Of course, you will usually see these in tables on a per unit mass basis, so they will be:
Entropy (SI Units) J/(kg*K) : Joules per kilogram Kelvin
Entropy (English) Btu/(lbm*R) : Btus per pound-mass degree Rankine

Answer 2

Like any thing we can know something about, we must be able to measure it. Without a proper unit we cannot say how much of it there is. Thei joule is a well defined unit of energy and the kelvin is a well defined unit of temperature. Using the combination of the two, we have defined a basic unit of entropy or disorder.

This definition is the simplest one, in that it represents the relationship between energy and temperature, which is a measure of disorder in a system.

Answer 3

If i get the question its because joules is a measure of energy and kelvin is a measure of temperature giving us a ratio of energy per degrees of temperature.But other than that reason its because that's how everyone decided to describe the measurement of Entropy.

Answer 4

Although entropy is easily explained as 'randomness', it is scientifically explained as heat transfer (energy) per degree of temperature (Kelvin) change. Hense, Joules/Kelvin.

Answer 5

because it's metric units although you find data in kJ/ºK sometimes depending on the substance