# why do things dissolve quicker in hot water

Dissolving. a simple reaction
What is going on? Have a look at the two rectangles. they are meant to show the water before it goes into the coffee cup. The green circles show what the molecules of water are doing (there are billions and billions of molecules in a cup of water - not just two! ). Water is a liquid that is completely made of molecules. these molecules are always moving. Sometimes the molecules move fast - sometimes slowly. When the water is hot the molecules move, but when it is cold the speed of the molecules is. You can make the molecules move faster by giving them some in the form of heat.

So how does temperature affect the Reaction Rate? So, if you give the molecules energy you will speed up the number of times they bump into each other Molecules are always doing what? If they have a lot of energy do the molecules move around fast or slow? What sort of energy will cause water molecules to move more? Will a 'hot' molecule move faster or slower than a 'cold' one? Can molecules react without bumping into each other? If the molecules have a lot of energy will they have to wait a long or a short time to bump into another one?

When you make coffee, do the hot water molecules move fast or slow? If you timed it for 1 minute, would the cold water molecules bump more or less times than the hot ones into the coffee molecules? Would the coffee dissolve completely in the cold water? Would the cold water take a long or a short time to dissolve the coffee? Todays experiment is very simple, but hopefully fascinating for even very young children. What you need Substances to try and dissolve eg. sugar, coffee, pepper, sand. Instructions Add a teaspoon of whichever solid you are testing to a glass of cold water and a glass of hot water, stir and observe the difference.

Look to see if the solid dissolves in the hot water and cold water and if one is better than the other. Can you design a chart to record your observations? The Science bit Things like salt, sugar and coffee dissolve in water. They are soluble. They usually dissolve faster and better in hot water. Pepper and sand are insoluble, they will not dissolve even in hot water. For older children Everything is made of particles which are always moving.

When a soluble solid ( solute ) is mixed with the right liquid (solvent), it forms a solution. This process is called dissolving. Two things that affect the speed at which the solid dissolves are temperature and the size of the grains of the solid. Caster sugar which is made of fine particles will dissolve quickly, but bigger sugar particles will take longer. Solids dissolve faster in hot water as in hot water the water molecules are moving faster, so bump into the solid more often which increases the rate of reaction.

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