Diffusion D. Crowley, 2007

Diffusion To understand, and be able to explain diffusion Saturday, May 16, 2015

State changes  Look at the particle theory diagrams of a solid, liquid and gas.  Copy out these boxes, and label the arrows showing the changes of state. The first one has been done for you… SolidLiquidGas LiquidSolid MeltingEvaporating CondensingFreezing

State Change See if you can fill in the correct boxes on the state changes…

Deodorant  What has deodorant got to do with diffusion?!  Who will smell the deodorant first if it is sprayed in the corner? When you smell it, put your hand up…  Why can you smell it, if its been sprayed over in the corner?

Deodorant  When deodorant is sprayed it doesn’t take long for everyone in the room to smell it  This is because the deodorant particles mix with the air particles. Remember, gas particles move quickly and randomly, in all directions. So wait enough time and eventually all those smelly particles will spread throughout the room  This is diffusion! Before diffusion After diffusion

Diffusion in gases  You don’t need to wave your arms around to mix the smelly particles - it mixes on its own  Diffusion in gases is very quick, because the particles in a gas move quickly, so they can get from one side of the class to the other quickly  Can you think when diffusion is useful / not so good?! Amorphophallus titanum - attracts insects with the smell of rotting meat - gas mixes in atmosphere due to diffusion

What about solids & liquids  Can diffusion happen in liquids?  Why do you think it can / cannot?  What about in solids?  Look at the demonstration - we are going to add some potassium manganate (solid) in the water.  What do you think will happen to the potassium manganate?  What do you notice?  The potassium manganate has dissolved in the water, giving a deep purple solution (as the potassium manganate particles diffuse in the water)  Now look at another solid, iron. Has the iron diffused into the water? How can you tell?

Which States Can Diffuse?  Remember the particle theory of solids, liquids and gases  In solids the particles are fixed in place (can only vibrate)  In liquids the particles can flow over each other  In gases, the particles move freely and randomly SolidLiquidGas  Diffusion is the mixing of particles, which occurs in gases and liquids but not solids  Diffusion can occur in gases and in liquids, because their particles are able to move  Diffusion is slower in liquids than in gases because the particles move more slowly  But diffusion cannot occur in solids - this is because the particles are fixed in place - they are not able to move (they can only vibrate), so do not mix Explain in your own words what diffusion is, and why it occurs in gases and liquids, but not solids…

Heat  How does heat affect the rate of diffusion?  Look at the demo using the potassium manganate again. What happens to the rate of diffusion when the temperature is increased?  Why does diffusion happen quicker in liquids and gases when they are heated? See if you can answer this question, thinking about what happens to the gas and liquid particles when they are heated…  Adding heat to the gas or liquid causes diffusion to happen quicker. This is because the particles have even more energy, and move around much quicker (mixing quicker) Have a go at home - place a tea bag in some water, and place another in some hot water