Suggest one reason not all the ammonia gas escaped?

Question

 

Wood was placed in a large glass tank with open bottle of concentrated ammonia solution, the tank was sealed NH3 gas escaped from the NH3 solution. Suggest one reason not all the ammonia gas escaped?

Answer 1

There is an equilibrium between gas and liquid that is reached over time because this is a closed system.  Vapor pressure is the name for this equilibrium.