What happens to carbonic acid in a degasifier/decarbonator at atmospheric pressure?

In a degasifier or decarbonator operating at atmospheric pressure, carbonic acid dissociates into water and carbon dioxide gas when conditions change, particularly the decrease in pressure. The purpose of such a system is to remove dissolved gases that can cause issues in water systems, such as scaling and corrosion.

When carbonic acid (H2CO3) comes in contact with lower pressures, it undergoes a reaction where it releases carbon dioxide (CO2) gas back into the atmosphere, effectively reducing its concentration in the water. This process is a key mechanism in maintaining the quality of water used in power generation and other industrial applications. The removal of CO2 aids in controlling the acidity of the water, preventing potential problems in boilers and other equipment. Hence, the release of carbon dioxide is the correct answer as it accurately reflects the chemical behavior of carbonic acid in the specified conditions.