Water—Where Does It Come from

In this chapter we address the question how the two elements hydrogen and oxygen that form a water molecule were formed during different evolutionary states of the universe and stars. 

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The lattice energy for sodium chloride is -788 kJ mol L This means that we need to supply (at least) +788 kJ mol to overcome the forces of attraction between the ions. But ah , [NaCl] is only +3.9kJ mol". Where does the energy needed to separate the ions come from The answer is that it comes from the strong attraction between the ions and the water molecules. 

For charge transport along chains with conjugated double bonds the mechanism of soliton motion has been proposed (this would be a theory for R-j in the terminology of the previous section). If the conjugation defect of Fig. h is called soliton , this term is used to stress two features of this defect it does not disperse while it moves (just as solitary water waves do not disperse. This is where the name comes from) and it has certain symmetry properties. If most polymer chains in today s polyacetylene films are very short, solitons will not be able to move very far since they are confined to the polyene chains. Therefore the non-dispersivity will be hard to test. In addition solitons will not be important for electrical conductivity under these circumstances. 

Wait about ten minutes and then feel the outside of the glass. Does it feel wet Can you see small drops of water on the glass How long did it take for water droplets to appear on the outside of the glass Why is there water on the outside of the glass Where do the water droplets come from ... 

Most of the formaldehyde you are exposed to in the environment is in the air. Formaldehyde dissolves easily in water, but it does not last a long time in water and is not commonly found in drinking water supplies. Most formaldehyde in the air also breaks down during the day. The breakdown products of formaldehyde in air include formic acid and carbon monoxide. Formaldehyde does not seem to build up in plants and animals, and although formaldehyde is found in some food, it is not found in large amounts. You will find more information about where formaldehyde comes from, how it behaves, and how long it remains in tlie environment in Chapter 5. 

The distinction is best made clear by means of an example Take the case of the chemical reaction which occurs between water and sulphuric acid Let us think of an apparatus similar to that indicated in Fig s In one vessel, A, there is a quantity of liquid water, and m contact with it some saturated vapour at pressure p0 The vapour fills the space on the left-hand side of the tap C In the vessel B there is some concentrated sulphuric acid, that is acid containing a little water, and above this acid is some vapour in equilibrium with the water in this sulphuric acid mixture The partial pressure of the water vapour is here p, where p is much less than pa This water vapour at low pressure (along with some sulphuric acid vapour which does not come into the calculation) occupies the space on the right of the tap C If we simply open the tap, water vapour would stream from left to right, that is from the region of high pressure p0 to that of low pressure p If a piston were placed in the tube it would be driven at a speed not by any means infinitely slowly, and the pressure difference on the two sides of the piston would be finite, 1 e (p0 - p ) This process, which is the spontaneous one, is an irreversible one, since the piston is not made to move infinitely slowly with infinitely small pressure difference on the two sides... 

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