Process classification – are isothermal and adiabatic processes necessarily reversible? Is it correct to regard isothermal processes and adiabatic processes as always reversible, or can they be reversible or irreversible depending on how they are conducted?

Introduction / Context:
Thermodynamic processes are classified both by path constraints (isothermal, adiabatic) and by reversibility. These classifications are independent; a process may satisfy a constraint yet still be irreversible.

Given Data / Assumptions:

• Isothermal: temperature held constant.
• Adiabatic: no heat transfer.
• Reversibility depends on absence of friction, infinitesimal gradients, and quasi-equilibrium.

Concept / Approach:
Reversibility is a quality of the path, not merely the constraint. An isothermal compression with finite temperature difference heat transfer or friction is irreversible. An adiabatic expansion across a throttle is irreversible; a reversible adiabatic process (isentropic) requires no dissipative effects.

Step-by-Step Solution:
Identify constraint (isothermal or adiabatic).Evaluate path characteristics: presence of friction, turbulence, finite ΔT heat transfer, unrestrained expansion → irreversibility.If all dissipations are eliminated and process is quasi-static, the same constraint can be satisfied reversibly.Therefore, such processes can be reversible or irreversible.

Verification / Alternative check:
Textbook examples: reversible adiabatic (isentropic) compression vs. throttling (adiabatic but irreversible); reversible isothermal expansion of an ideal gas vs. isothermal mixing/compression with friction (irreversible).

Why Other Options Are Wrong:

• “Reversible process” or “irreversible process” alone overgeneralise.
• “None of these” ignores established thermodynamic distinctions.

Common Pitfalls:
Equating “adiabatic” with “isentropic” without the reversibility requirement; isentropic = adiabatic + reversible.

Final Answer:
reversible or irreversible process