Question

The internal energy of a system is dependent on the following aspects:

1) Molecular weight

2) Molecular structure

3) Degree of molecular activity

Which of the above are correct?
1. 1 and 2 only
2. 1 and 3 only
3. 2 and 3 only
4. 1, 2 and 3

Answer 1

Correct Answer - Option 4 : 1, 2 and 3

Explanation:

• There are two types of internal energy of a system i.e. macroscopic and microscopic.
• From a thermodynamic point of view, we will focus on the microscopic approach i.e. at the molecular level.
• The microscopic energy consists of energy at the molecular level e.g. molecular rotation, vibration, etc. and energy at the nuclear level is also involved.
• The rotational and vibrational energy also depends upon the molecular structure e.g. inertia of molecules depends upon how the atoms are arranged.
• So, the internal energy of a system is dependent on molecular structure and the degree of molecular activity. 
• Internal energy is an extensive property, so it depends on mass and volume, hence it depends on molecular weight.