55 total
Everything, including living cells, is made of atoms, molecules and ions. These particles are always moving. The higher the temperature, the faster they move. This is because the particles have more kinetic energy at higher temperatures. The more kinetic energy they have, the faster they move.
In solids: Particles cannot move very far because they are held together by attractive forces between them. They simply vibrate around a fixed position.
In liquids: Particles can move more freely but stay in contact with one another. They bump into one another and rebound.
In gases: Particles are freer still, with no attractive forces between the molecules or atoms.
In solutions: When molecules and ions are in a solution, they can move as freely as when they are liquid.
🔑 Key Point: Particles are always in random motion, and this movement is essential for diffusion to occur.
Diffusion is the net movement of particles from a region of their higher concentration to a region of their lower concentration (i.e. down a concentration gradient), as a result of their random movement.
Imagine a rotten egg full of hydrogen sulfide gas in one corner of a room. Hydrogen sulfide gas is very smelly. To begin with, there is a high concentration of the gas near the egg but none in the rest of the room. The hydrogen sulfide molecules quickly spread through the air in the whole room. Soon, you cannot tell where the smell first came from – the whole room smells of rotten egg! This spreading out is called diffusion.
The random movements of gas molecules result in them spreading evenly through all the space available. Initially, there is a high concentration of hydrogen sulfide molecules in one corner, but over time, molecules spread evenly through the space available.
Sign in to view full notes