in this video we're going to talk about the rate of dissolving that means how fast a solute dissolves in a solvent we'll talk about a few factors that affect this rate the rate of dissolving can vary quite a lot let's say we have one teaspoon of sugar and we're dissolving it in a glass of water in one situation that sugar could fully dissolve in just a few seconds in another situation it could take hours for the sugar to fully dissolve we'll look at the three main factors that influence the rate of dissolving these factors are the size of the pieces that we're dissolving stirring the solution and the temperature you've probably encountered all three of these in your own experiences and we'll talk about them one by one let's begin with the size of the pieces or particles that we're dissolving let's say we're dissolving sugar into water this sugar can come in different forms for example we could have a sugar cube or we could have granulated sugar from a packet we could have the same amount of sugar in these different forms but each will dissolve at different speeds so if we do this what are we going to see well the sugar cube will dissolve slower and the granulated sugar will be faster to dissolve now what can we say about the size of the pieces here well for the sugar cube we're talking about the cube itself so that's pretty large the granulated sugar if we look at it up close we'd see it's made of tiny little grains almost like grains of sand so the size of the pieces is way smaller here so what's the relationship between these sizes and the rate of dissolving here well the smaller pieces dissolve faster larger pieces dissolve more slowly so the smaller the size of the pieces the faster the substance dissolves that's the main point let's take a minute and talk about why this is it really has to do with a surface area of the pieces of solute for example on the sugar cube surface area is the amount of surface on the solute that is exposed to the outside here all the faces of the sugar cube are exposed to the outside to see why surface area affects dissolving let's take a look at a diagram of the dissolving process at the atomic level this is a 3d diagram but to make things a little clearer let's look at a 2d diagram this sort of shows us an atomic view of the dissolving process these gray circles represent particles of sugar which is the solute and these blue circles represent particles of water which is the solvent when a solid dissolves solvent molecules interact with the solute particles at the surface of the solute and they carry the solute particles into solution you can see it right here some of these solute particles on the surface are dissolved and get carried away but a solute can only dissolve from its surface the solute in here can interact with a solvent which is all the way out here so if you want something to dissolve faster create more surface or more surface area so how would you do that well you'd make the pieces smaller here's another 2d view of our sugar cube imagine you smash it up into smaller pieces a sugar cube has a relatively small surface area in a sugar cube most of the sugar is hidden inside the cube it can't touch the solvent and has to wait to be exposed before it can be dissolved so the cube dissolves slowly but when a solid is finely granulated and broken into smaller pieces there is larger surface area available to interact with solvent you're basically taking sugar that was inside the cube and bringing it to the outside so that it can touch solvent so more sugar is on the outside here all of these surfaces can touch or interact with solvent molecules and so dissolving can happen in all of these places here so it dissolves more quickly and you could crush these chunks into even smaller pieces you would expose even more surface area to the solvent the solvent can now interact with all the solute that used to be trapped inside these pieces it can get into all of these areas here and these pieces would dissolve even faster so the main point here is smaller pieces more surface area faster dissolving let's move to stirring or agitation agitation is sort of a technical word that refers to mixing or moving something around after you put the sugar into the water what do you do you stir it if you do more stirring you get faster dissolving and why is that stirring moves the solvent particles around let's look at another diagram and we'll see why this is important here we see some sugar getting dissolved in water we'll use orange particles to represent the sugar here when the solvent molecules surround or solvate the sugar particles they can't dissolve anymore they become sort of occupied these dissolved sugar particles are surrounded by water and those water molecules can't really pull away any more sugar they're busy with the sugar particles they're already attached to but imagine that you stirred this mixture you'd move these occupied solvent molecules and spread them around the stirring moves these occupied water molecules away the stirring also brings fresh water molecules in contact with the sugar those new water molecules can then interact with the sugar help pull them away and do more dissolving so essentially this process brings more water molecules into contact with undissolved sugar and all of the stirring will cause faster dissolving finally let's consider the effect of temperature on the rate of solution here's the trend at higher temperature there's a higher rate of dissolving why is this well remember that temperature has to do with kinetic energy or how fast particles move the higher the temperature the higher the kinetic energy that means that solvent particles will move faster so at higher temperature these solvent particles the water molecules here are going to be moving around faster so they will literally bump into the solute more often because they're moving faster they're also going to be banging into the solute particles with more force and that will make it easier for the solute particles to break away from the solid surface and become solid now it's important to take just a minute and mention the difference between the speed that something dissolves and the amount that can dissolve increasing the temperature affects both of these it increases the speed of dissolving which we call the rate and it also increases the amount that dissolves which we call the solubility but don't confuse these two rate has nothing to do with how much can dissolve only how fast it can dissolve for example imagine that you have one teaspoon of sugar in hot tea and cold tea the sugar dissolves faster in the hot tea but because temperature also affects solubility we'd be able to dissolve even more sugar in the hot tea than in the cold tea so now you can see the three factors that increase the rate of how something dissolves you can crush the solute into smaller pieces which increases the surface area you can agitate or stir which brings fresh solvent in contact with a solute and you can increase the temperature which gives the particles more speed and energy so that they collide more often and with more force think about all three of these the next time you dissolve a sugar cube into your tea