Heat
In physics and thermodynamics, heat is the process of energy transfer from one body or system due to thermal contact, which in turn is defined as an energy transfer to a body in any other way than due to work performed on the body.Energy transfer by heat can occur between objects by radiation, conduction and convection. Energy can only be transferred by heat between objects - or areas within an object - with different temperatures ( Zeroth law of thermodynamics ). This transfer happens spontaneously only in the direction of the colder body ( Second law of thermodynamics ).
Zeroth Law of Thermodynamics:
A system is said to be in thermal equilibrium when its temperature does not change over time. Let A, B, and C be distinct thermodynamic systems or bodies. The zeroth law of thermodynamics can then be expressed as:
"If A and C are each in thermal equilibrium with B, A is also in thermal equilibrium with C."
If two bodies are in thermal equilibrium with a third body,then the two bodies are in thermal equilibrium with each other.
If T(A) = T(B)
And T(B) = T(C)
Then T(A) = T(C)
First Law of Thermodynamics :
The first law of thermodynamics, an expression of the principle of conservation of energy, states that energy can be transformed (changed from one form to another), but cannot be created or destroyed.
"The change in the internal energy of a system is equal to the amount of energy added by heating the
system minus the amount lost as a result of the work done by the system on its surroundings."
Second Law of Thermodynamics :
The second law of thermodynamics is an expression of the universal principle of decay observable in nature. It is measured and expressed in terms of a property called entropy, stating that the entropy of anisolated system which is not in equilibrium will tend to increase over time, approaching a maximum value at equilibrium; and that the entropy change dS of a system undergoing any infinitesimal reversible process is given by δq/T, where δq is the heat supplied to the system and T is the absolute temperature of the system.
Versions of the law
- In a system, a process that occurs will tend to increase the total entropy of the universe.
- Heat generally cannot flow spontaneously from a material at lower temperature to a material at higher temperature.
- It is impossible to convert heat completely into work in a cyclic process.
- In the neighbourhood of any equilibrium state of a thermodynamic system, there are equilibrium states that are adiabatically inaccessible.