How is the solubility of most gases and solids in water affected by the temperature of the water?

Answer 1

OK, disclaimer: There are a lot of things going on in the details here both chemically, and in reference to the laws of thermodynamics, but here is a fairly simplified explanation.

Basically when a liquid is warm its molecules are moving around a bunch. In fact they are moving around much faster than the molecules of a solid at the same temperature. This means that the liquid molecules are constantly smashing into the molecules of the solid and transferring their energy. This in turn causes the solid to become more pliable. Thus solids become more soluble when they come into contact with liquids of higher temperatures. This is why boiling water in a particularly grimy pan will help do most of the cleaning for you, and why sugar dissolves faster in hot coffee.

Conversely, gas particles move faster than liquid particles of the same temperature. So if you want a liquid, like water, to hold more gas you have to slow its particles down by cooling it. This essentially traps the gas particles in a traffic jam of liquid molecules. The gas particles move around in the spaces between liquid molecules without colliding with them very often. This means they don't transfer much energy to the liquid, but thanks to the law of diffusion, a larger amount of them will remain trapped in the spaces between the liquid particles. This is easily demonstrated by shaking a warm soda and a cold one and then opening them. The cold one will foam less because less gas will be able to escape the liquid, whereas the warm one will make a big mess because a large amount of gas will be able to escape quickly.

Answer 2

The solubility of solids in water increases as the temperature goes up and decreases as the temperature goes down. That means as the water gets hotter, you can dissolve more sugar, salt, etc. in it. The cooler water gets, the less you an dissolve in it. When water has as much of the solid dissolved in it as possible, the solution is called saturated.

The opposite is true for a gas. Colder water can dissolve more gas than warmer water. That is why soda or seltzer poured into a glass starts giving off bubbles. The liquid has carbon dioxide gas dissolved in it and as the liquid starts getting warmer in the glass, the gas leaves the solution as bubbles. Similarly, when you boil water, it is hot enough for any gas dissolved in the water to bubble out of the solution giving the boiling effect.