First law of thermodynamics: judge the correctness of the statement Statement: “In the first law of thermodynamics, the total energy of the system remains constant.” Choose whether the statement is correct or incorrect.

Concept/Approach

• The first law is an energy balance: the change in a system's total energy equals heat added minus work done by the system.
• It does not say the system's energy is always constant; only an isolated system (Q = W = 0) keeps constant energy.

Key relationΔE = Q − WE includes U (internal), KE, and PE.

ExampleAt constant volume heating: W = 0 ⇒ ΔE = Q > 0, so energy increases.

Final AnswerDisagree — the system's energy need not remain constant; it changes per ΔE = Q − W.