Part I FIRST LAW OF THERMODYNAMICS

The video introduces the First Law of Thermodynamics, noting it's one of three laws, with the first covering thermal equilibrium, the second heat, and the third entropy. The focus of this session is on the concepts behind the First Law.

A thermodynamic system is defined as any collection of objects considered a unit, with the potential to exchange energy with its surroundings. An example given is a kettle with popcorn, where adding heat causes the popcorn to pop, indicating a change in internal energy within the system. This process is called a thermodynamic process.

The video explains the sign conventions for heat (Q) and work (W). Positive Q means heat is absorbed by the system, while negative Q means heat is released. Positive W means work is done *by* the system, and negative W means work is done *on* the system by the surroundings.

Work done during volume changes is discussed. For varying pressure, work is the integral of pressure (P) with respect to volume (dV). For constant pressure, work is calculated as P times the change in volume (V2 - V1), illustrating that work occurs when volume changes in a thermodynamic system.

Pressure-Volume (PV) diagrams are introduced as a way to visualize work done. The area under the curve in a PV diagram represents the work done by the system. If work is greater than zero, there's a decrease in volume and pressure. If work is less than zero, volume increases. For constant pressure, the area (work) is greater than zero, with volume changing while pressure remains constant.

The concept of thermodynamic paths is explored, showing how different paths between states affect work done. Examples include paths where volume is constant but pressure changes, or pressure is constant but volume changes. The video demonstrates that thermodynamic processes are path-dependent, meaning the amount of work done varies with the specific path taken between states.

The video concludes by summarizing the initial concepts of thermodynamic systems, the paths of thermodynamic processes, and the work done during volume changes under varying pressure conditions.