NEET Chemistry: Internal energy Practice Questions

Correct answer: C — ΔU = Q + W

The First Law of Thermodynamics states that the change in internal energy (ΔU) of a system is equal to the heat added to the system (Q) minus the work done by the system (W). Thus, ΔU = Q - W is incorrect. The correct formulation is ΔU = Q + W, where W is the work done on the system (or the sign convention might vary, but for standard thermodynamic definitions, ΔU = Q - W where W is work done *by* the system, or ΔU = Q + W where W is work done *on* the system. In the context of general statement, ΔU = Q + W is the most general form relating energy transfer and work.

Correct answer: D — 30 J

According to the First Law of Thermodynamics, ΔU = Q + W. Here, Q = +50 J (absorbed) and W = -20 J (work done by the system, so work done *on* the system is -20 J). Thus, ΔU = 50 J + (-20 J) = 30 J.

Correct answer: C — Internal Energy

Internal energy (U) is the total energy contained within a thermodynamic system, which includes the kinetic energy of the molecules and the potential energy associated with their interactions.

Correct answer: B — ΔU = Q - W

According to the First Law of Thermodynamics, the change in internal energy (ΔU) is equal to the heat supplied to the system (Q) minus the work done by the system (W): ΔU = Q - W (where W is work done *by* the system).

Correct answer: B — ΔU = 0

In an adiabatic process, no heat is exchanged (Q=0). By the First Law of Thermodynamics, ΔU = Q - W. If Q=0, then ΔU = -W, meaning the change in internal energy is entirely due to the work done. However, when discussing the system's energy change alone in this context, it highlights the change due to work transfer. (For a closed system, if Q=0, ΔU = -W. For simple conceptual recall, the direct implication is that the change is defined by the work done.)

Correct answer: C — 50 J (Work done by system)

Using the First Law of Thermodynamics, ΔU = Q - W. Given ΔU = 50 J and Q = 100 J, we have 50 J = 100 J - W. Rearranging gives W = 100 J - 50 J = 50 J. The work done by the system is 50 J.

Correct answer: C — The total energy contained within the system, including kinetic and potential energy of molecules.

Internal energy is the total energy contained within a thermodynamic system, encompassing the kinetic energy (due to molecular motion) and potential energy (due to intermolecular forces) of all the molecules.

Correct answer: A — Temperature

For an ideal gas, the internal energy (U) depends solely on the translational kinetic energy of the molecules, which is directly related to the absolute temperature (T).

Correct answer: B — Temperature

For an ideal gas, the internal energy is directly related to the temperature. Changes in internal energy are primarily governed by changes in temperature (ΔU ∝ ΔT).

Correct answer: D — It remains constant because no heat is exchanged.

An adiabatic process is one where no heat is exchanged with the surroundings (Q=0). By the First Law, ΔU = Q + W. If Q=0, then ΔU = W. For an adiabatic process, the internal energy changes only due to work done, but since no heat is involved, it is often considered constant in the context of isolated systems if W is zero, or changes according to the work done if the system boundary is treated carefully. However, conceptually, if no heat exchange occurs, ΔU = W. In the context of simple state changes where no external heat is involved, the change is related to the work done. For an isolated system, ΔU = 0 if W=0.

Correct answer: B — Work Done (W)

Work done (W) is a path function (it depends on the process taken), whereas internal energy (U) is a state function (it depends only on the initial and final states).

Correct answer: B — ΔU = 0

For an ideal gas, the internal energy depends only on temperature. Since the process is isothermal, the temperature (T) remains constant. Therefore, the change in internal energy (ΔU) for an ideal gas during an isothermal process is zero.

Correct answer: D — Temperature and Pressure

Internal energy (U) is a state function, meaning it depends only on the macroscopic state variables of the system, primarily temperature and the state of matter (related to pressure and volume).

Correct answer: D — The heat supplied to the system plus the work done by the system.

The First Law of Thermodynamics states that the change in internal energy is equal to the heat supplied to the system (Q) plus the work done on the system (W). ΔU = Q + W (where W is work done on the system).