SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/eng-first-law-energy-balance

With work W defined as done by a system, what is its internal-energy change?

The first law gives delta U = Q - W.

Start playing free

  1. Q - W ✔
  2. Q + W
  3. W - Q

Why: Heat added raises internal energy, while work done by the system removes energy from it. Sign conventions can differ, so engineers must define W before using the equation.

Huh, didn't know that: Internal energy is a state function, but heat and work depend on the path between states.

The dad joke
Energy never disappears, it just changes departments.
Like this card?
Play the game

References

Answer: Q - W. Heat added raises internal energy, while work done by the system removes energy from it. Sign conventions can differ, so engineers must define W before using the equation.

  1. OpenStax University Physics Volume 2, First Law of Thermodynamics openstax.org/books/university-physics-volume-2/pages/3-3-first-law-of-thermodynamics
    The first law states that the change in internal energy of that system is given by Q-W.
    Checked 2026-10-10.

Think this answer is wrong? Tap "Challenge this answer" on the card in the game and tell us why.

Test yourself in the game

EngineeringHow many base units does the International System of Units (SI) have?EngineeringSince the SI redefinition voted in 2018, what defines the kilogram?EngineeringIn today's SI, how precisely is the value of the Planck constant known?

That's stuff everyone should know.