NEET Chemistry: Work Practice Questions

Correct answer: C — 70 J

Using the First Law of Thermodynamics: ΔU = Q - W. Here, Q = +100 J (absorbed heat) and W = +30 J (work done by the system). Therefore, ΔU = 100 J - 30 J = 70 J.

Correct answer: D — w = ΔU

For an isothermal process, the change in work is equal to the change in internal energy, as ΔU = 0 for an ideal gas, thus w = ΔU.

Correct answer: D — Change in Internal Energy

Work done (W) is fundamentally related to the change in the system's internal energy (ΔU) when heat is not considered. For a process, the First Law of Thermodynamics states ΔU = Q - W.

Correct answer: C — W = 0

Since the volume does not change (ΔV = 0), the work done (W = -PΔV) during an isochoric process is zero.

Correct answer: D — Work done is independent of the path taken by the process.

Work done (W) is related to the change in internal energy (ΔU) by the formula W = -ΔU. This definition holds regardless of the specific path taken during the process.

Correct answer: D — First Law of Thermodynamics

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

Correct answer: C — Work done by the system in an isothermal expansion

Work done by the system is positive when the system expands (volume increases). For an isothermal expansion, the work done is W = -PΔV (where ΔV is positive), meaning work done *by* the system is negative, or W = PΔV if we consider the change in energy balance. In the context of thermodynamic work definition, expansion means positive work done *by* the system to the surroundings (or vice versa, depending on the sign convention).

Correct answer: C — Work (w)

Work (w) is the energy transferred when a force (like pressure) acts over a distance (volume change); it is the mechanical energy exchanged during a process.

Correct answer: D — Zero work, as no external force is applied

A free expansion means the expansion occurs into a vacuum, meaning no external pressure is exerted on the surroundings. Since no work is done against an external force, the work done by the system is zero.

Correct answer: D — P dV

Work done (W) in a general thermodynamic process is defined as the integral of pressure with respect to volume, W = ∫ P dV.

Correct answer: C — W = PΔV

For an isobaric process (constant pressure P), the work done is calculated as W = PΔV, where ΔV is the change in volume.

Correct answer: B — ΔU is positive

According to the First Law of Thermodynamics, ΔU = Q - W. If heat is absorbed (Q>0) and work is done by the system (W>0), the change in internal energy depends on the net transfer. If the system absorbs heat and does work, ΔU is not necessarily positive or negative; it depends on the net heat transfer. However, in introductory context, if heat is absorbed and work is done *by* the system, the change in internal energy is determined by the net energy exchange. A simpler conceptual framing is that work done *by* the system decreases its internal energy if heat is not added. (If Q is absorbed, ΔU = Q - W).

Correct answer: C — Internal Energy

For a reversible process, the work done (W) is related to the change in internal energy (ΔU) and heat (Q) by the First Law of Thermodynamics: ΔU = Q - W. Therefore, work done is W = Q - ΔU. If we consider a process where ΔU is known, W is derived from the relationship. More fundamentally, work is the energy transfer associated with a change in state, directly related to the change in energy (Internal Energy).

Correct answer: C — W (Work)

W represents the work done in or on the system. It quantifies the energy transfer associated with mechanical interactions (like expansion or compression) between the system and its surroundings.

Correct answer: A — Positive

Spontaneous expansion means the system does work on the surroundings, resulting in positive work done by the system (w > 0).