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Energy & Heat

Energy Formula

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 โˆ†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.

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

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

State & Path Functionsโ€‹

State vs. Path

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