Heat Capacity

Heat capacity (usually denoted by a capital C, often with subscripts), or thermal capacity, is the measurable physical quantity that characterizes the amount of heat required to change a substance's temperature by a given amount. In the International System of Units (SI), heat capacity is expressed in units of joule(s) (J) per kelvin (K).

Derived quantities that specify heat capacity as an intensive property, i.e., independent of the size of a sample, are the molar heat capacity, which is the heat capacity per mole of a pure substance, and the specific heat capacity, often simply called specific heat, which is the heat capacity per unit mass of a material. Occasionally, in engineering contexts, a volumetric heat capacity is used. Because heat capacities of materials tend to mirror the number of atoms or particles they contain, when intensive heat capacities of various substances are expressed directly or indirectly per particle number, they tend to vary within a much more narrow range.

Temperature reflects the average kinetic energy of particles in matter while heat is the transfer of thermal energy from high to low temperature regions. Thermal energy transmitted by heat is stored as kinetic energy of atoms as they move, and in molecules as they rotate. Additionally, some thermal energy may be stored as the potential energy associated with higher-energy modes of vibration, whenever they occur in interatomic bonds in any substance. Translation, rotation, and a combination of the two types of energy in vibration (kinetic and potential) of atoms represent the degrees of freedom of motion which classically contribute to the heat capacity of atomic matter (loosely bound electrons occasionally also participate). On a microscopic scale, each system particle absorbs thermal energy among the few degrees of freedom available to it, and at high enough temperatures, this process contributes to a specific heat capacity that classically approaches a value per mole of particles that is set by the Dulong-Petit law. This limit, which is about 25 joules per kelvin for each mole of atoms, is achieved by many solid substances at room temperature (see table below).

For quantum mechanical reasons, at any given temperature, some of these degrees of freedom may be unavailable, or only partially available, to store thermal energy. In such cases, the specific heat capacity will be a fraction of the maximum. As the temperature approaches absolute zero, the specific heat capacity of a system also approaches zero, due to loss of available degrees of freedom. Quantum theory can be used to quantitatively predict specific heat capacities in simple systems.

Read more about Heat CapacityBackground, Older Units and English Units, Extensive and Intensive Quantities, Metrology, The Measurement of Heat Capacity, Table of Specific Heat Capacities, Specific Heat Capacity of Building Materials

Other articles related to "heat capacity, heat":

Specific Heat Capacity of Building Materials
... See also Thermal mass (Usually of interest to builders and solar designers) Specific heat capacity of building materials Substance Phase cp J/(g·K) Asphalt solid 0.920 Brick solid 0.840 ...
Classical And Quantum Conductivity - Conductivity - Flaws in Classical Conductivity
... The molar heat capacity of a metal is expected to be (3/2)R greater than that of insulators, which has a heat capacity of 3R ... In other words, it is expected that the molar heat capacity of metals will be (9/2)R ... The experimentally determined molar heat capacity of metals is close to 3R ...
Convective Heat Transfer - Newton's Law of Cooling - Solution in Terms of Object Heat Capacity
... which is proportional to simple total heat capacity, and, the temperature of the body, or, it is expected that the system will experience exponential decay ... From the definition of heat capacity comes the relation ... (The total heat capacity of a system may be further represented by its mass-specific heat capacity multiplied by its mass, so that the time constant is also given by ) ...
Schottky Anomaly
... effect in solid state physics where the specific heat capacity of a solid at low temperature has a peak ... It is called anomalous because the heat capacity usually increases with temperature, or stays constant ... approaches the difference between the energy levels there is a broad peak in the specific heat corresponding to a large change in entropy for a small change in temperature ...
Thermal Effusivity
... of the product of the material's thermal conductivity and its volumetric heat capacity Here, k is the thermal conductivity, is the density and is the specific heat capacity ... The product of and is known as the volumetric heat capacity ...

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