Energy & Heat

Energy is the capacity to do work (denoted by w) or transfer heat (denoted by q). Usually, energy is measured in Joules or Calories.

Before talking about what ∆E is (as shown above), it's important to understand what a system is and what the surroundings are.

• A system is the object being studied or the focus of the problem.
• The surroundings are everything else outside of this system/object.

∆E represents the change in energy, and the sign of this is very important.

• Whenever ∆E is negative, energy is lost to the surroundings.
• When ∆E is positive, however, energy is gained from the surroundings.

State & Path Functions

To describe a process, it is usually called a state or path function.

• State functions are dependent on the initial and final states of a system.
  • Typically represented by uppercase variables.
  • Ex. V, E, P, T
• Path functions on the other hand are dependent on the path that a system takes to get from the initial to the final state.
  • They are represented by lowercase variables.
  • Ex. q, w, t, d