【Daily Question】Theoretical Foundation 2019.6.6

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Multiple-choice question: Which of the following statements is consistent with the first law of thermodynamics? ( ) (A) When a chemical reaction occurs in a completely adiabatic and rigidly bounded closed container, its internal energy must change. (B) In a process without work exchange, the change in internal energy equals the heat transferred during the process; this indicates that the increase in internal energy is not necessarily independent of the thermodynamic process. (C) When a closed system undergoes an adiabatic change between two specified equilibrium states, the work done by the system is independent of the path taken. (D) During an adiabatic expansion or compression of a gas, the change in its internal energy is independent of the manner in which the process takes place. Answer: C. Because during adiabatic conditions, ΔU = Q + W = W. In (A), there is no heat exchange and no volume work, so ΔU = Q + W = 0. (B) In a reactive process, ΔU = Q, which indicates that the initial and final states are the same and that the heat amount is constant; this does not mean that the change in internal energy is related to the process. In (D), since the work done during an adiabatic reversible expansion and an adiabatic irreversible expansion is clearly different, ΔU is also different. This is not contradictory to the fact that internal energy is a state function, because starting from the same initial state, an adiabatic reversible expansion and an adiabatic irreversible expansion cannot lead to the same final state. Tip: The answer can be seen in the reply