2. The First Law of Thermodynamics

2. The First Law of Thermodynamics

Concept Explanation:

The first law of thermodynamics, also known as the law of energy conservation, states that the total energy of an isolated system remains constant. Energy can be transferred between the system and its surroundings in the form of work or heat, but it cannot be created or destroyed. Mathematically, the first law of thermodynamics is expressed as:

ΔU = Q + W

where:
• ΔU is the change in internal energy,
• Q is the heat added to the system (positive when heat is added to the system, negative when heat is lost),
• W is the work done on the system (positive when work is done on the system, negative when the system does work on the surroundings).

This law emphasizes the conservation of energy in all thermodynamic processes.

Example Problem:

A system absorbs 500 J of heat and does 200 J of work on its surroundings. What is the change in the system’s internal energy?

Solution:

Using the first law of thermodynamics:

ΔU = Q + W

Given:
• Q = 500 J (heat absorbed by the system),
• W = -200 J (work done by the system),

ΔU = 500 J - 200 J = 300 J

So, the internal energy of the system increases by 300 J.