Technology & Engineering
Negative Heat Capacity
Negative heat capacity is a phenomenon where the temperature of a system decreases as its internal energy increases. This is contrary to the usual behavior of matter, where an increase in energy leads to an increase in temperature. Negative heat capacity is observed in some systems, such as certain types of lasers and self-gravitating systems.
Written by Perlego with AI-assistance
Related key terms
1 of 5
3 Key excerpts on "Negative Heat Capacity"
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
____________________ WORLD TECHNOLOGIES ____________________ Alternatively, using base 2 logarithms, C * relates the base-2 logarithmic increase in temperature to the increase in the dimensionless entropy measured in bits. Heat capacity at absolute zero From the definition of entropy the absolute entropy can be calculated by integrating from zero kelvins temperature to the final temperature T f The heat capacity must be zero at zero temperature in order for the above integral not to yield an infinite absolute entropy, which would violate the third law of thermodynamics. One of the strengths of the Debye model is that (unlike the preceding Einstein model) it predicts the proper mathematical form of the approach of heat capacity toward zero, as absolute zero temperature is approached. Negative Heat Capacity (stars) Most physical systems exhibit a positive heat capacity. However, even though it can seem paradoxical at first, there are some systems for which the heat capacity is negative . These include gravitating objects such as stars; and also sometimes some nano-scale clusters of a few tens of atoms, close to a phase transition. A Negative Heat Capacity can result in a negative temperature. According to the virial theorem, for a self-gravitating body like a star or an interstellar gas cloud, the average potential energy U Pot and the average kinetic energy U Kin are locked together in the relation The total energy U (= U Pot + U Kin ) therefore obeys If the system loses energy, for example by radiating energy away into space, the average kinetic energy and with it the average temperature actually increases . The system therefore can be said to have a Negative Heat Capacity. A more extreme version of this occurs with black holes. According to black hole thermodynamics, the more mass and energy a black hole absorbs, the colder it becomes.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter- 3 Heat Capacity Heat capacity (usually denoted by a capital C , often with subscripts) is the measurable physical quantity that characterizes the amount of heat required to change a body's temperature by a given amount. In the International System of Units, heat capacity is expressed in units of joules per kelvin. Derived quantities include the molar heat capacity , which is the heat capacity per mole of a pure substance. Similarly, specific heat capacity (also called more properly mass-specific heat capacity or more loosely specific heat), is the heat capacity per unit mass of a body. These quantities are intensive quantities. That is, they are not dependent on amount of material, but directly reflect the type of material, as well as the physical conditions of heating. Temperature reflects the average total kinetic energy of particles in matter. Heat is transfer of thermal energy; it flows from regions of high temperature to regions of low temperature. Thermal energy is stored as kinetic energy and, in molecules and solids, also as potential energy in the modes of vibration or phonons. These represent degrees of freedom of movement for atoms. These degrees of freedom, and sometimes others, contribute to the heat capacity of a thermodynamic system. As the temperature appro-aches absolute zero, the specific heat capacity of a system also approaches zero. Quantum theory can be used to quantitatively predict specific heat capacities in simple systems. Background Before the development of modern thermodynamics, it was thought that heat was a fluid, the so-called caloric . Bodies were capable of holding a certain amount of this fluid, hence the term heat capacity , named and first investigated by Joseph Black in the 1750s. Today one instead discusses the internal energy of a system. This is made up of its microscopic kinetic and potential energy.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter- 1 Heat Capacity Heat capacity (usually denoted by a capital C , often with subscripts) is the measurable physical quantity that characterizes the amount of heat required to change a body's temperature by a given amount. In the International System of Units, heat capacity is expressed in units of joules per kelvin. Derived quantities include the molar heat capacity , which is the heat capacity per mole of a pure substance. Similarly, specific heat capacity (also called more properly mass-specific heat capacity or more loosely specific heat), is the heat capacity per unit mass of a body. These quantities are intensive quantities. That is, they are not dependent on amount of material, but directly reflect the type of material, as well as the physical conditions of heating. Temperature reflects the average total kinetic energy of particles in matter. Heat is transfer of thermal energy; it flows from regions of high temperature to regions of low temperature. Thermal energy is stored as kinetic energy and, in molecules and solids, also as potential energy in the modes of vibration or phonons. These represent degrees of freedom of movement for atoms. These degrees of freedom, and sometimes others, contribute to the heat capacity of a thermodynamic system. As the temperature approaches absolute zero, the specific heat capacity of a system also approaches zero. Quantum theory can be used to quantitatively predict specific heat capacities in simple systems. Background Before the development of modern thermodynamics, it was thought that heat was a fluid, the so-called caloric . Bodies were capable of holding a certain amount of this fluid, hence the term heat capacity , named and first investigated by Joseph Black in the 1750s. Today one instead discusses the internal energy of a system. This is made up of its microscopic kinetic and potential energy.
Index pages curate the most relevant extracts from our library of academic textbooks. They’ve been created using an in-house natural language model (NLM), each adding context and meaning to key research topics.
