# Concentration of gas in water: What is the time derivative of concentration toward steady state?

The Henry's law gives the steady state concentration for a gas in water. But it does not tell about the speed for this to happen if the concentration is not in steady state. What is the time derivative of concentration of oxygen in gas?

The transient diffusion equation for the oxygen concentration is $$\frac{\partial C}{\partial t}=D\frac{\partial^2 C}{\partial x^2}$$where D is the diffusion coefficient. Henry's law applies at the interface.