Heating water at atmospheric pressure: When liquid water is heated in an open vessel exposed to the atmosphere, the primary thermodynamic path is best described as what type of process?

Introduction / Context:
Thermodynamic path labels help classify processes and simplify energy balances. Everyday heating of water in an open pot is a common example to identify whether pressure, volume, or temperature is held approximately constant.

Given Data / Assumptions:

• Open vessel exposed to the atmosphere (pressure ~ constant at 1 atm).
• Liquid water expands slightly with temperature; volume is not fixed.
• Significant heat is added; temperatures change until boiling.

Concept / Approach:
In an open container, the system is at atmospheric pressure; any expansion work is done against a nearly constant external pressure. Temperature rises during sensible heating, so the process is not isothermal. Heat is supplied, so it is not adiabatic. Volume is not constrained, so it is not isochoric.

Step-by-Step Solution:
Identify boundary condition: constant external pressure ≈ 1 atm.Observe that temperature changes from ambient to near 100°C.Volume changes slightly; fixed volume is not enforced.Therefore, the process is best approximated as isobaric.

Verification / Alternative check:
Enthalpy-based heat calculations use ΔH = ∫ Cp dT for open, constant-pressure heating, matching kitchen and process heater scenarios.

Why Other Options Are Wrong:
Isochoric requires rigid, sealed volume; adiabatic would require perfect insulation; isothermal would require heat removal or phase change balance to keep T constant.

Common Pitfalls:

• Equating small volume changes with constant volume; open heating does not constrain V.
• Assuming boiling portion is isothermal; that occurs only at the phase change temperature with heat of vaporization.

Final Answer:
Isobaric (constant pressure)