Temperature is a measurement of a substance’s average kinetic energy per molecule. It is distinct from heat, despite the fact that the two variables are inextricably linked. The energy transferred between two things at different temperatures is referred to as heat.

## Temperature

Temperature is the attribute of a substance that defines the quantity of heat present in it. Temperature expresses the degree of hotness or coldness of a body as a function of its average kinetic energy.

Kelvin is the standard unit (or SI unit) of temperature.

## Temperature Scales

Temperature can be measured on a number of various scales, but the most common are Fahrenheit, Celsius, and Kelvin.

Those who live in the United States and a few other nations are most familiar with the Fahrenheit scale. On this scale, water freezes at 32 degrees Fahrenheit and boils at 212 degrees Fahrenheit.

In most other countries throughout the world, the Celsius scale (sometimes known as centigrade) is used. Water has a freezing point of 0 degrees Celsius and a boiling temperature of 100 degrees Celsius on this scale.

The scientific standard is the Kelvin scale, which is named after Lord Kelvin. On this scale, 0 represents absolute zero, which is the point at which all molecular motion ceases. It is a temperature scale that is considered absolute.

## Absolute Zero

The Kelvin (K) scale is the absolute temperature scale that corresponds to the Celsius scale, while the Rankine (R) scale is the absolute temperature scale that corresponds to the Fahrenheit scale. On both absolute scales, the zero points represent the same physical state.

Absolute zero is the coldest theoretical temperature, at which the thermal motion of atoms and molecules is at its lowest. This is the point at which the enthalpy and entropy of a cooled ideal gas have reached their lowest value, which is 0. This is a state of motionlessness, but quantum uncertainty states that the particles nevertheless have a limited zero-point energy. On the Kelvin scale, absolute zero is 0 K, -273.15 °C on Celsius scale, and -459.67 °F on Fahrenheit scale.

## Relation Between the Temperature in Kelvin and in Celsius scale

Relation between the temperature in Kelvin and in Celsius scale is given as

Kelvin = degree celsius + 273.15

## Comparison of Kelvin, Celsius and Fahrenheit Temperature Scales

### Kelvin Scale

The Kelvin scale is a centigrade scale for measuring thermodynamic temperature, with the kelvin as the unit of measurement. In the International System of Units (SI), the kelvin is the base unit of temperature and is denoted by the letter K.

### Celsius Scale

Anders Celsius, a Swedish astronomer, proposed the Celsius scale in 1742.

Water has a freezing point of 0 degrees Celsius and a boiling point of 100 degrees Celsius in standard atmospheric condition in Celsius scale. Atmospheric pressure is used to determine both temperatures.

### Fahrenheit Scale

In 1724, German scientist Daniel Fahrenheit, the originator of the mercury thermometer, developed this scale. Fahrenheit measured a mixture of ice, water, and ammonium chloride at 0 degrees Fahrenheit, the temperature of water as ice forms on it at 32 degrees Fahrenheit, and the human body at 96 degrees Fahrenheit. Later, the scale was modified slightly to make the human body temperature 98.2 degrees Fahrenheit, and it became popular all over the world due to the extremely precise measurements Fahrenheit’s thermometers provided. Most countries, however, have switched to the Celsius system.

## Third Law of Thermodynamics

As the temperature approaches absolute zero, the entropy of a system approaches a constant value.

This law stated as the entropy of a pure crystalline substance is zero at absolute zero of temperature, 0 K, and that it is impossible to reduce the temperature of a system to absolute zero in a finite number of steps using any mechanism, no matter how idealised. This enables us to establish a zero point for a body’s thermal energy.

### Conclusion

Temperature expresses the degree of hotness or coldness of a body as a function of its average kinetic energy.

Temperature can be measured on a number of various scales, but the most common are Fahrenheit, Celsius, and Kelvin.

Absolute zero is the coldest theoretical temperature, at which the thermal motion of atoms and molecules is at its lowest.

On the Kelvin scale, absolute zero is 0 K, -273.15 °C on Celsius scale, and -459.67 °F on Fahrenheit scale.

Relation between the temperature in Kelvin and in Celsius scale is given as

Kelvin = degree celsius + 273.15

The Kelvin scale is a centigrade scale for measuring thermodynamic temperature, with the kelvin as the unit of measurement.

Water has a freezing point of 0 degrees Celsius and a boiling point of 100 degrees Celsius in standard atmospheric condition in Celsius scale.

Fahrenheit measured a mixture of ice, water, and ammonium chloride at 0 degrees Fahrenheit.