Question

Define combined form of first and second law of thermodynamics.

Answer 1

Hint : We know that the relationship of heat with the other forms of energy is the branch of science which is called thermodynamics. To be more precise, it is a study of thermal energy and how it is converted and how it affects the matter when the conversion of the energy is taking place.

Complete Step By Step Answer:
We should know that thermodynamics is the branch of physics that deals with the relationships between heat and other forms of energy. In particular, it describes how thermal energy is converted to and from other forms of energy and how it affects matter. Properties can be combined to express internal energy and thermodynamic potentials, which are useful for determining conditions for equilibrium and spontaneous processes. With these tools, thermodynamics can be used to describe how systems respond to changes in their environment. Thermodynamics, science of the relationship between heat, work, temperature, and energy. In broad terms, thermodynamics deals with the transfer of energy from one place to another and from one form to another. In thermodynamic, the combined law of thermodynamics also called Gibbs fundamental equation m is a mathematical summation of the first law of thermodynamics and the second law of thermodynamic summed into a single concise mathematical statement as: $dU-TdS+Pdv\le 0$
Where $~dV$ is variation in the volume of a simple working body in which there is neither flow of particles out of the body nor external forces, other than gravity on the body. In theoretical structure, in addition to the obvious inclusion of the first two laws, the combined law incorporates the implications of the zeroth law, via temperature T and the third law, through its use of free energy as related to the calculation of chemical affinities near absolute zero.

Additional Information:
The network involved in a cyclic process is the area enclosed in a $P-V$ diagram. If the cycle goes clockwise, the system does work. If the cycle goes anticlockwise, then the work is done on the system every cycle. An example of such a system is a refrigerator or air conditioner. The change in energy in a cyclic process is zero, since the initial and final states are the same. The work done and the quantity of heat gained in such a process are therefore the same with opposite signs.

Note :
Remember that it should be known that a cyclic process consists of a series of changes which return the system back to its initial state. In noncyclic processes the series of changes involved do not return the system back to its initial state.