Thermodynamic Laws

Understanding the laws of thermodynamics and energy conservation

Topics

How do heat engines work?

Heat engines convert thermal energy (heat) into mechanical work by using a working fluid that expands when heated and contracts when cooled. They operate in cycles, taking heat from a hot source, converting some to work, and rejecting waste heat to a cold sink.

What is entropy?

Entropy is a measure of disorder or randomness in a system. According to the second law of thermodynamics, entropy always increases in isolated systems, meaning systems naturally become more disordered over time.

What is the first law of thermodynamics?

The first law of thermodynamics states that energy cannot be created or destroyed, only converted from one form to another. The change in a system's internal energy equals the heat added minus the work done by the system.

What is the second law of thermodynamics?

The second law of thermodynamics states that entropy (disorder) always increases in isolated systems, and heat cannot spontaneously flow from cold to hot. This law explains why processes are irreversible and why 100% efficient engines are impossible.

Why can't we have 100% efficient engines?

We can't have 100% efficient engines because the second law of thermodynamics requires that some heat must be rejected to a cold sink. Heat engines need a temperature difference to operate, and some waste heat is inevitable, making perfect efficiency impossible.