Specific heat capacity

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The specific heat capacity (symbol c or s, also called specific heat) of a substance is defined as heat capacity per unit mass. The SI unit for specific heat capacity is the joule per kilogram kelvin, J·kg-1·K-1 or J/(kg·K), which is the amount of energy required to raise the temperature of one kilogram of the substance by one kelvin. Heat capacity can be measured by using calorimetry.

The equivalent definition using cgs units is the amount of energy (measured in ergs) required to raise the temperature of one gram of the substance by one degree Celsius (erg/(g·°C)). Other units of specific heat capacity include calories per gram degree Celsius (cal/(g·°C) or cal/(g·K)) and Btu per pound degree Fahrenheit (Btu/(lb·°F))

The symbol cp is often used to denote specific heat capacity at constant pressure.

Substances with low specific heat such as metals require less input energy to increase their temperature. Substances with high specific heat such as water require much more energy to increase their temperature. The specific heat can also be interpreted as a measure of how well a substance preserves its temperature, i.e. "stores" heat, hence the term "heat capacity".

Factors that influence heat capacity measurements

  • Temperature: Measuring the heat capacity of water produces different results if the starting point is 20 °C rather than 60 °C. Therefore the temperature at which the measurement was conducted must be specified for the value to be useful.
  • Intermolecular forces: Strong intermolecular forces combined with a disordered state (such as hydrogen bonding in liquid water) are likely to increase the heat capacity of a substance. In the case of an ideal gas, intermolecular forces are absent from the system, and the specific heat capacity is independent of pressure. Helium behaves like an ideal gas at standard ambient temperature and pressure
  • For a gas, it is necessary to distinguish between specific heat at constant pressure (usually noted ) and at constant volume (usually noted ). The former, which is also the most commonly used, applies to a gas evolving at constant pressure, and the latter applies to a gas evolving at constant volume, such as a gas in air-tight enclosure. Two distinct capacities can also be defined for liquids and solids, however the difference between the two is generally not worth considering: liquids and solids are nearly incompressible, so that their thermodynamic behavior is not significantly affected by pressure.

Table of specific heat capacities

Substance Phase Specific
heat capacity
Air (dry) gas 1005
Air (100% humidity) gas ≈ 1030
Aluminium solid 900
Brass solid 377
Copper solid 385
Diamond solid 502
Ethanol liquid 2460
Gold solid 129
Graphite solid 720
Helium gas 5190
Hydrogen gas 14300
Iron solid 444
Lithium solid 3582
Mercury liquid 139
Nitrogen gas 1042
Oil liquid ≈ 2000
Oxygen gas 920
Water gas 1850
liquid 4186
solid (0 °C) 2060
Standard ambient temperature and pressure
used unless otherwise noted. For gases, the value given corresponds to

See also

External links

  • WebElements: [1]

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