Temperature

One of the fundamental quantities in science is temperature, which is a measure of the average amount of kinetic energy, a system contains.

When the temperature increases, the motion of these particles also increases.  In other words, temperature determines the internal energy within a given system.

Temperature is measured with a thermometer or a calorimeter. Temperatures are expressed using scales that use units called degrees.

Figure 1: There are three scales used for reporting temperatures. 

The Celsius scale (symbolised by °C and spoken as “degrees Celsius”) defines 0°C as the freezing point of water and 100 °C as the boiling point of water. 

This scale is divided into 100 divisions between these two landmarks and extended higher and lower as well.

Note that science uses the Celsius and Kelvin scales.  The United States is one of the few countries in the world that still uses the Fahrenheit scale daily.

The SI unit for temperature is the Kelvin (K). 

The Kelvin temperature scale uses degrees that are the same size as the Celsius degree, but the numerical scale is shifted up by 273.15 units. That is, the conversion between the Kelvin and Celsius scales is as follows:

K=⁰C+273.15

For example: 16⁰C in Kelvin = 16 + 273 = 289K

For most purposes, it is acceptable to use 273 instead of 273.15.  

Note that the Kelvin scale does not use the word degrees; a temperature of 295 K is spoken of as “two hundred ninety-five kelvin” and not “two hundred ninety-five degrees Kelvin.”

The reason that the Kelvin scale is defined this way is that there exists a minimum possible temperature called absolute zero (zero Kelvin). The Kelvin temperature scale is set so that 0 K is absolute zero, and the temperature is counted upward from there.

Heat vs Temperature

It is important to understand that heat and temperature are not the same. Although the two concepts are linked, they mean different things.

Heat describes the transfer of thermal energy between molecules within a system and it is measured in joules. An object can gain or lose heat, but it cannot have heat. Heat is not a property possessed by an object or system rather it is a measure of change.

In conclusion, we can say that heat is a transfer of thermal energy caused by a difference in temperature between molecules.