Question

What are 1st and 2nd laws of thermodynamics?

Answer 1

Hint: Thermodynamics is a branch of physics which deals with work, heat, temperature and their relation to physical properties of matter, energy etc. Thermodynamic laws give us relation between the thermodynamic variables for different systems. The first law gives us a relation between internal energy, heat and works done while the second law
gives us a relation between entropy and different types of processes.

Complete answer:
A branch of physics dealing with work, temperature and heat and their relations to radiation, energy and physical properties of matter is called thermodynamics.
The first law of thermodynamics states that the total internal energy of a body is the difference of the heat transferred to the system and the work done by the system. Therefore,
$\Delta U=Q-W$
Here, $\Delta U$ is the change in the internal energy of the system
$Q$ is the heat transferred to the system
$W$ is the work done by the system
The first law of thermodynamics is in accordance with the law of conservation of energy.
The entropy is a thermodynamic variable which determines whether a process is spontaneous or nonspontaneous. The second law of thermodynamics states that, A natural process which starts in one equilibrium state but ends in a different equilibrium state will move in a direction which causes the entropy of the system and environment to increase for an irreversible process but remain constant for a reversible process. Therefore,
${{S}_{f}}>{{S}_{i}}$ [ for irreversible process]
${{S}_{f}}={{S}_{i}}$ [ for reversible process]
Here, ${{S}_{f}}$ is the final entropy
${{S}_{i}}$ is the initial entropy
 Therefore, the first law of thermodynamics gives us a relation between internal energy of a system, heat transferred and work done. The second law of thermodynamics tells us about entropy as a state variable and the value of entropy for reversible and irreversible processes.

Note:
A state variable is a property of matter which depends on the initial and final states of a system. The path variable is the property which depends on the path taken to reach the final state. The important properties of matter in thermodynamics are the pressure, volume, energy, density etc.