Why is the Specific Heat Capacities of Metals so Low

The specific heat capacity of a material is the amount of heat energy needed to heat 1 kg of the material by 1° Celsius. The table presented below, presents the specific heat capacity of some metals at constant pressure (c p ) at a temperature of 25° Celsius.

Metal Element

Specific Heat Capacity at Constant Pressure (25° Celsius) J / g K

Aluminum

0.897

Antimony

0.207

Bismuth

0.123

Cadmium

0.231

Chromium

0.449

Copper

0.385

Gold

0.129

Iron

0.450

Lead

0.129

Mercury

0.1395

Magnesium

1.02

Silver

0.233

Tin

0.227

Zinc

0.387

Tungsten

0.134


Specific Heat Capacities of Certain Compounds

The specific heat capacities of a selection of compounds is shown below. They are much higher than the metals.

Compound/Mixture

Specific Heat Capacity at Constant Pressure (25° Celsius) J/g K

Air at 0° Celsius

1.0035

Ammonia

4.700

Hydrogen Sulfide

1.015

Methane at 2° Celsius

2.191

Paraffin Wax

2.5

Solid Polyethylene

2.3027

Ice (-10° Celsius)

2.11

Water (25° Celsius)

4.1813

Ethyl Alcohol at 20° Celsius

2.4

The reason is that when a metal is heated, most of the heat energy is used to increase the kinetic energy of the free electrons. Very little is used to increase the vibrational kinetic energy of the atoms in the lattice. The electrons are much less heavy than the atoms and are easily heated. In contrast, the atoms in the compounds in the table above have no free electrons, so any energy is used to increase the energy of the atoms. It takes much more energy to do this, so the specific heat capacity is much higher.