If a gas is dissolved in water and the partial pressure of the gas above the liquid is zero (open atmosphere), the dissolved gas will not escape completely immediately. However, over time, the dissolved gas may slowly escape from the water until it reaches equilibrium with the partial pressure of the gas in the surrounding atmosphere.
The process by which a gas dissolves in water is influenced by several factors, including the solubility of the gas in water, temperature, pressure, and the presence of any other dissolved substances. When a gas dissolves in water, it forms intermolecular interactions with water molecules, which can hold the gas molecules within the liquid.
When the partial pressure of the gas above the liquid is zero, it means that there is no additional pressure driving the gas to dissolve further. However, the dissolved gas will still be in equilibrium with the gas phase, and individual gas molecules will continue to leave and enter the liquid.
Over time, the dissolved gas molecules near the liquid surface may escape into the gas phase, and an equal number of gas molecules from the gas phase may dissolve into the liquid. This process is known as "evaporation" or "degassing." The rate of degassing will depend on factors such as the solubility of the gas, temperature, and the surface area of the liquid exposed to the gas.
Eventually, when equilibrium is reached, the rate of gas molecules leaving the liquid will be equal to the rate of gas molecules entering the liquid, resulting in a constant concentration of the dissolved gas. At this point, the amount of gas escaping from the liquid will be balanced by the amount of gas dissolving back into the liquid.
It's important to note that the specific behavior and rate of degassing will depend on the properties of the gas, the characteristics of the liquid, and the specific conditions of the system.