They are then said to be in thermal equilibrium.Īs with work, the amount of heat transferred depends upon the path and not simply on the initial and final conditions of the system. When the flow of heat stops, they are said to be at the same temperature. Heat transfer occurs by conduction or by thermal radiation. When a temperature difference does exist, heat flows spontaneously from the warmer system to the colder system. In general, when two objects are brought into thermal contact, heat will flow between them until they come into equilibrium with each other. In this case, there is energy transfer between these two blocks, and heat flows from the hotter to the cooler block by these random vibrations. If a hotter block of metal is put in contact with a cooler block, the intensely oscillating atoms at the edge of the hotter block give off their kinetic energy to the less oscillating atoms at the edge of the cool block. At low temperatures, the atoms continue to oscillate but with less intensity. However, the transfer of energy as heat occurs at the molecular level due to a temperature difference.Ĭonsider a metal block at high temperature that consists of atoms oscillating intensely around their average positions.
Heat is a form of energy, but it is energy in transit. While internal energy refers to the total energy of all the molecules within the object, heat is the amount of energy flowing spontaneously from one body to another due to their temperature difference. You can only break even at absolute zero.ģ. It is sometimes stated as a general adage without specific reference to the laws of thermodynamics.ġ.
(a consequence of the third law of thermodynamics) (a consequence of the second law of thermodynamics)ģ. (a consequence of the first law of thermodynamics)Ģ. Popular version of the consequences of the first, second, and third laws of thermodynamics:ġ. This allows us to define a zero point for the thermal energy of a body. The entropy of a system approaches a constant value as the temperature approaches absolute zero.īased on empirical evidence, this law states that the entropy of a pure crystalline substance is zero at the absolute zero of temperature, 0 K and that it is impossible using any process, no matter how idealized, to reduce the temperature of a system to absolute zero in a finite number of steps. It follows perpetual motion machines of the second kind are impossible. From this law, it is impossible to construct a device that operates on a cycle and whose sole effect is the transfer of heat from a cooler body to a hotter body. Reversible processes are a useful and convenient theoretical fiction but do not occur in nature. This law indicates the irreversibility of natural processes.
In a natural thermodynamic process, the sum of the entropies of the interacting thermodynamic systems increases.
The entropy of any isolated system never decreases. It follows perpetual motion machines of the first kind are impossible. It is the most important law for analyzing most systems and quantifying how thermal energy is transformed to other forms of energy. This law is the principle of conservation of energy. The increase in internal energy of a closed system is equal to the heat supplied to the system minus work done by it. This law provides a definition and method of defining temperatures, perhaps the most important intensive property of a system when dealing with thermal energy conversion problems. If two systems are both in thermal equilibrium with a third, then they are in thermal equilibrium with each other. These are considered as one of the most important laws in all of physics. Four laws of thermodynamics define fundamental physical quantities (temperature, energy, and entropy) and characterize thermodynamic systems at thermal equilibrium.