Why do sugar granules dissolve faster in liquids when you stir them with a spoon, than just leaving it to sit?
In: Chemistry
When something starts dissolving in water, it increases the amount of stuff dissolved in that particular part of water. The more stuff is already dissolved, the less likely it is that more dissolves into it.
If you just leave it sit, diffusion is the only process that carries the dissolved molecules away so fresh water without anything dissolved can come by to pick up more molecules. If you stir, you artificially accelerate the carrying-away of dissolved molecules, making more space for new ones to dissolve faster.
Think of a drop of food dye getting put in a cup of water. You can see the color floating around in the water, but there are still parts of the water that don’t have dye in them. Stirring the water helps push the dye into the parts of the water that don’t have dye yet, and once the water is mixed with dye you can’t un-stir it back into water and dye.
Sugar works in a similar way, except it starts out as solid crystals instead of a liquid. Water molecules have space between them that the sugar molecules can hide in. Stirring the water helps evenly distribute the sugar to all these hiding places.
Once the space between the molecules is all taken up by sugar, you can’t dissolve any more sugar and its called a saturated liquid. No matter how much you stir after saturation, there will always be sugar that can’t dissolve because there’s no more room to hide. Warming the water can make it able to dissolve more sugar because warm things expand. Warm things expanding is because the space between the molecules gets bigger, which means there’s more space between the molecules for sugar to hide and more can be dissolved.
There must be an increased surface area exposed on the sugar crystals too as you break them up and agitate them?
Sugar dissolving in water is a chemical reaction. In this case, between the sugar molecules and water molecules. One of the ways to speed up a reaction is to increase the amount of interactions between the molecules, so by stirring the water you are actually increasing the chances of a sugar molecule “bumping” into a molecule of water.
Dissolving is a process whose rate is related to the amount already in the solution, and the surface area. By stirring you are constantly moving new solvent (water in this case) past the materials ( sugar)
It is not unlike cooling an object by blowing air on it.
Agitation assists in the dissolving process. It’s one of the factors that increases solubility
Think of each grain like a little bar of soap. Rub them around, and they’ll wear down faster.
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