Physics Van 3-site Navigational Menu

Physics Van Navigational Menu

Q & A: chemical equilibria

Learn more physics!

Most recent answer: 10/22/2007
Q:
Can a chemical reaction occur if the reactants are in the product at the time of creation? So could hydrogen and oxygen form water if they were in water? Also, how do gases manage to be dissolved in water? Thanks
- Harold (age 33)
A:
Sure, 2H2 and O2 can combine to make 2H2O when they are already in water. However, your question seems based on another important consideration. Every reaction can also happen in reverse. So in H2O, there is also a (low) rate of forming H2 and O2. There's an equilibrium set of concentrations in which these opposite rates just cancel.

Mike W.

Gases dissolve in water just like other substances. The entropy of a gas/water system is increased when there is mixing. Many gases have little solubility in water, such as helium. Water is a polar molecule, and there are strong electric fields between the molecules of water. These can induce electric dipole moments in atoms or molecules of gases. Gases that are more electrically polarizable, or which have dangling hydrogen atoms which can hydrogen-bond with water molecules are highly soluble in water. One of the gases most easily dissolved in water is ammonia, NH3 -- at standard temperature and pressure, you can get 54 grams per 100 ml of water dissolved.

Another gas which dissolves readily is carbon dioxide. In solution, this actually forms carbonic acid.

Tom

(published on 10/22/2007)

Follow-up on this answer.