quarta-feira, 28 de março de 2012


When someone is cooking and you are sitting there in you living room and you suddenly feel a mouth watering smell, you know it is food. You then realise that the smell is spread all over your house. But how?
This is called diffusion. When chemicals such as the smell of your perfume or the smell of your favourite plate, are let in a room, the particles mix together(the air particles+the substance's particles).
You really don't need to shake your arms to spread the gas particles, they bounce(move around) by themselves.
When gases diffuse it is very quick, since they move quickly...

Diffusion can also happen inliquids, but it takes more time. This is because the particles in liquids can move around each other, and so, they get mixed, but since the gas particles move quicker, diffusion in liquids is slower. 

Diffusion does NOT happen in solids. This is because particles in a solid can only vibrate in it's place.

How diffusion works?

Now, answer the quiz:

Simple diffusion is defined as the movement of
A)molecules from areas of higher concentration to areas of lower concentration.
B)molecules from areas of lower concentration to areas of higher concentration.
C)water molecules across a membrane.
D)gas molecules across a membrane.
E)gas or water molecules across a membrane.

2When sugar is mixed with water, equilibrium is reached when
A)molecules of sugar stop moving.
B)water and sugar molecules are moving at the same speed.
C)the dissolved sugar molecules are evenly distributed throughout the solution.
D)there are the same number of water molecules as dissolved sugar molecules.
E)two tablespoons of coffee are added.

3The rate of diffusion is affected by which of the following?
B)size of molecules
C)steepness of the concentration gradient
D)A and B
E)A, B and C

4The molecules in a solid lump of sugar do not move.

5Diffusion is one of the processes whereby materials are exchanged between a cell and its environment.



A) molecules from areas of higher concentration to areas of lower concentration.
This is the correct answer.


This is the correct answer.

C)the dissolved sugar molecules are evenly distributed throughout the solution.


This is the correct answer.

E)A, B and C


This is the correct answer.


This is the correct answer.

Flowing (diffusion) of Particles


Solids can't flow because their particles can only  vibrate and can't move from place to place. SOLIDS CAN'T FLOW!


Liquids can flow because their particles can slide over each other. When water is poured into a glass, the particles of the water slide over each other and into the corners of the glass. Like when  we did in class, the liquid was diffusing and it showed how liquids flow. LIQUIDS CAN FLOW, BECAUSE THEY MOVE! 


Gases can flow because their particles can move in all directions, their particles move randomly. When a Bunsen burner is connected to a gas tap and turned on, naturally the  gas flows through the rubber tube, making it's way to it's destination, which in this case is the Bunsen burner. Particles in the gas have loads of kinetic energy they can move anywhere the want! Remember when we experienced the gas flowing, the gas particles spread all around the class, and everyone could smell.

Expansion and Contraction

Have you ever wondered why does things expand because of the heat? Yes, it has to do with PARTICLES.
Substances expand when they get heated up and they contract when they cool down.
Uh?  What about the thermometre? How does it measure the substances' temperature, if it is expanding?
But that is exactly because of expansion and contraction that it can tell you the temperature, they work because the liquid inside them rises up the tube when it gets hotter.
But expansion and contraction can also cause problems. Think of a bridge, in Summer, with the heat, it would expand, and that is why we have special joints to stop them bending out of shape. 

What is important for you to know is that the particles does NOT grow or shrink, they will always be the same size. The thing that changes is the space between them. 

Solids-It's particles vibrate more when is heated and so, take up more room.

Liquids- The particles move more around each other, taking up more space.

Gases- Move more quicklyin all direction when is heated up.

More about solids, liquids and gases:

States of Matter

Diagram of melting ice:

a) The ice cube in the beginning when the temperature is low and it is still in a fixed shape.

b) When the ice cube is melting and the forces between particles are increasing because it is getting more kinetic energy.

c) The particles gained loads of energy and now it reached it boiling point, and the particles will melt and they all will turn into steam.