Topic: Diffusion.
Why can we smell hot food from a distance?
Hey.
Looks like you have lost your way.
No.
I know the way.
Fine.
Don't listen.
See, I told you.
Now listen to me.
There is a restaurant next to your house where hot sizzling food is available, right?
Yeah.
Yummy.
Follow its smell and you will reach home.
I have reached home.
Do you know how the smell of that food reached you?
When food gets cooked, it releases some aromatic gases into the air.
The molecules of these gases spread and mix with air molecules.
When this air reaches our nose, we get the smell of food.
This process of spreading and mixing of a substance with another substance is called diffusion.
But then, why couldn't I smell the food inside my house from a distance?
This is because that food had become cold.
On heating food, the molecules of its aromatic gases gain kinetic energy and start vibrating faster.
They spread and mix easily into air, leading to an increased rate of diffusion.
As the food gets cold, the temperature of the aromatic gases decreases.
The kinetic energy of molecules decreases and they do not vibrate as much anymore.
Thus, the rate of diffusion decreases and we cannot smell the food from a distance.