Nature of heat and work in thermodynamics — select the correct statement Which of the following statements correctly characterizes heat and work in thermodynamics?

Introduction / Context:
Correctly distinguishing properties from interactions is essential. State properties (like pressure, temperature, internal energy) belong to the system at an instant, whereas heat and work are modes of energy transfer across the boundary during a process.

Given Data / Assumptions:

• System boundaries are well defined.
• Processes are considered between equilibrium states.
• Sign conventions for heat/work are standard (engineering or physics, as long as consistent).

Concept / Approach:
Heat and work are not contained in a system; they occur only while a process is taking place and always involve the boundary. Consequently, they are path functions—dependent on the process path, not solely on initial and final states—unlike properties, which are point functions determined by state variables alone.

Step-by-Step Solution:
Evaluate A: Boundary phenomena — correct, since no “heat in a system” exists except as energy transfer across the boundary.Evaluate B: Energy in transit — correct; heat/work are the means by which energy crosses boundaries.Evaluate C: Path functions — correct; different paths between same states can yield different Q and W values.Therefore, all three statements are true ⇒ select “all of the above.”

Verification / Alternative check:
In cyclic processes returning to the same state, ΔE = 0 but ∮δQ and ∮δW need not be zero and often are nonzero, demonstrating their path dependence.

Why Other Options Are Wrong:
Option E contradicts the fundamental definition; heat and work are not properties.

Common Pitfalls:
Speaking of “heat content” of a system—more precise terms are internal energy, enthalpy, or specific heat capacity.

Final Answer:
all of the above