Project ForgeA closed vessel contains pure water in thermal equilibrium with its vapour at 25°C (Stage #1), with ambient air outside also at 25°C, 1 atm. The vessel is then kept inside an isothermal oven with hot air maintained at 80°C, and attains a new thermal equilibrium (Stage #2). If Valve A (connecting the vessel's vapour space to the oven atmosphere) is now opened inside the oven, what will happen immediately after opening the valve?
- AWater vapor inside the vessel will come out of the Valve A
- Hot air will go inside the vessel through Valve A
- CNothing will happen — the vessel will continue to remain in equilibrium
- DAll the vapor inside the vessel will immediately condense
Explanation
At Stage #2, the vessel's internal pressure equals the saturation pressure of water at 80°C, about 47.4 kPa — far below the surrounding oven's 1 atm (≈101.3 kPa) air pressure. Since the outside pressure is much higher than the inside pressure, opening the valve lets the higher-pressure hot air rush INTO the vessel.
Source: GATE ME 2020 Session 2 (ME-2) (2020)
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