N°4 – Specific heat (A level)

Specific heat is the quantity of heat which needs to be applied to 1 [kg] of a body to raise its temperature by 1 [°C] (1 [K]).

It enables the calculation of the quantities of heat to be applied or to be removed to heat or to cool the body, without modifying its physical state (solid, liquid, gas).
Hence, to raise the temperature of 1 [kg] of water by 1 [°C] (1[K]), the quantity of heat to be applied is 4180 joules (4.18 [kJ], 3.96 Btu).

The symbol for specific heat is C.

C_water= 4.18 [kJ/kg.K] (3.96 Btu/kg.K)

The specific heat depends on the molecular configuration of a body.
It differs also for each type of matter, and for a given type of matter it also depends on its physical state (solid, liquid or gas).
Hence it needs:

• Approx. 2.1 [kJ] to heat 1 [kg] of ice by 1 [°C] or [K]: C_ice = 2.1 [kJ/kg.K] (1.99 Btu / kg K)
• Approx. 4.18 [kJ] to heat 1 [kg] of water by 1 [°C] or [K]: C_water = 4.18 [kJ/kg. K] (3.96 Btu/kg.K)
• Approx. 1.83 [kJ] to heat 1 [kg] of steam by 1 [°C] or [K]: C_steam = 1.83 [kJ/kg.K] (1.74 Btu/kg.K)

In our professional branch of activity, for normal levels of temperature we will use for water and for air:

• C_water= 4.18 [kJ / kg K] (3.96 Btu/kg.K)
•  C_air= 1 [kJ / kg K] (0.95 Btu/kg.K)

If we have to heat or cool other types of matter, we will find all the necessary specific heat and density values on the internet.