When rice is boiling over, why do the bubbles immediately go down when you lift the lid?
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Turning boiling-temp water into steam takes a HUGE amount of energy. When the lid is on and the steam condenses and drops as back into the pot, this energy is kept in the system. The hot pot is only losing heat through its walls to the surrounding air.
When you lift the lid, you have the same amount of heat being added to the pot (from the stove below), but now suddenly WAY more heat leaving the pot. All the energy that went into turning the water into steam is now leaving the pot as the steam leaves.
The same amount of heat energy going in and much more heat energy going out means the temperature in the pot rapidly drops, which quickly slows or stops the boiling inside.
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