For a closed system, you need two things:
1) a conservation of mass within the boundaries of the system
2) the ability to freely exchange energy to & from the "closed" system with a surrounding external system
So, the answer is <u><em>never</em></u>, since your defining the "system" as the water within the bathtub, and an open bathtub is exposed to evaporation, which is not conserving mass within the defined "system".
The cornea does not contain any blood vessels, but instead contains many nerve endings that make it extremely sensitive. That is why a scratch or a loose eyelash is so painful.
The atoms which make up the ion are covalently bonded to one another. 19) It is possible for a compound<span> to possess </span>both ionic and covalent bonding<span>. a. If one of the </span>ions<span> is polyatomic then there will be </span>covalent bonding<span> within it.</span>
If you dilute a concentrated solution, the concentration of the obtained solution is smaller than that of the initial solution. But if you add more solute to a concentrated solution, the concentration of the obtained solution is greater than that of the initial.
