Introduction: The First Law of Thermodynamics refers to the notion that energy can be neither created nor destroyed, so the energy in the universe is constant. In problems that involve the first law of thermodynamics, an isolated part of the universe (the system) is surrounded from the rest of the universe (the surroundings). The First Law of Thermodynamics is represented by the equation written below:

U=q+w, where U=internal energy, q=heat transferred into or out of the system, and 

w=work done on or by the system

Generally, when heat is transferred into the system, q>0, and q<0 when heat is transferred out of the system. On the other hand, when work is done on the system by the surroundings, w>0, while w<0 when work is done by the system.

The First Law of Thermodynamics is important because it governs processes relating to car engines, battery operation, food consumption, and photosynthesis, among other processes. In car engines, for example, chemical energy is converted into kinetic energy. On the other hand, batteries convert chemical energy into electrical energy.

Directions for This Lesson: In this lesson, you will learn about the first law of thermodynamics. First, try the practice questions to determine what you already know about the first law of thermodynamics. Then, watch the video lesson to learn more about the first law of thermodynamics.