Question

The first law of thermodynamics
1. is a re-statement of the law of conservation of energy when applied to thermodynamic systems.
2. is the basis for the definition of internal energy.
3. is basis for the definition of temperature.

• A. 1 and 2 are correct
• B. Only 1 is correct
• C. Only 2 is correct
• D. Both 2 and 3 are correct

Answer 1

The correct option is A 1 and 2 are correct

First law is gives the conservation of energy in thermodynamic systems. It is given by
$\Delta Q=\Delta W+\Delta U......\left(1\right)$
Some part of energy supplied to a system has to be used in raising the internal energy of the system and rest is used for doing work.
Thus, energy is conserved.
Also,
First law is the basis for defining change in Internal energy.
The change is internal energy of the system is equal to the difference between the heat added to the system and work done by the system.
From $\left(1\right)$, we write that
$\text{Change in internal energy}\left(\Delta U\right)=\text{Heat added to the system}\left(Q\right)-\text{Work done by the system}\left(W\right)$
Definition of temperature is given by Zeroth law of thermodynamics, not by the first law.
Thus, option (a) is the correct answer.