Molar Heat Capacity Explained

While there are only 92 naturally occurring elements, there are innumerable compounds which are formed through their combination. Every compound is characterized by certain physical parameters and one of the most important ones is its molar heat capacity.

Heat capacity is the amount of heat, that needs to be supplied to a compound, to raise its temperature by some degrees. Depending on the molecular structure of a substance and the kind of internal bonding, the heat required to raise a substance's temperature, through a specific amount of degrees will vary.

Specific heat capacity is the amount of heat (usually measured in joules), required to raise the temperature of a single gram of substance, through one degree Celsius or one degree Kelvin.

The molecular weight of the substance, expressed in grams is known as a single mole. It is known to contain 6.023 x 10²³ molecules. For example, the molar mass of water is approximately 18 gm/mol.

The molar heat capacity of a substance is the amount of heat required to raise the temperature of one mole of a substance or compound through one degree Celsius. Since the molecular weight and structure of each compound varies, every substance has a unique value.

Every physical quantity, including the molar heat capacity needs to be specified with the proper units. The units used for it, are 'Joule/mol K' or 'Joule Per Mole Kelvin'. It is theoretically possible to calculate it from its specific heat capacity. Here is the formula:

Molar Heat Capacity (Joules/Mol K) = [Specific Heat Capacity (Joules/gm K) x Molar Mass (gm/Mol)]

This formula simplifies calculation substantially, if you have the value of specific heat capacity of the substance and the knowledge of its molar mass.

To use the above formula for any substance, you need to know how to calculate molar mass and have a reference chart that has the specific heat capacity of that substance.

The molar mass of water is approximately 18 gm/mol and its specific heat capacity is 4.1813 Joule/gm K (at 25° Celsius).

Molar Heat Capacity of Water = (4.1813 Joule/gm K) x (18 gm/mol) = 75.2634 Joule/Mol K

Calculating this parameter for any element is an experiment which you will surely perform as a part of your first chemistry lab course. It is an important step in what is known as the characterization of any compound.

You could either determine it experimentally or theoretically from the knowledge of specific heat capacity.