Question

What happens when air is heated?

Answer 1

Hint: When air is heated, the molecule starts vibrating and the molecules get collided with each other. As a result, there is more space created. Air expands when it is heated and contracts when it is cooled.

Complete step by step answer:
As we already knew, when air is heated, the molecule starts vibrating and the molecules get collided with each other. As a result, there is more space created. The molecules freely move in the space and it expands.
The more space also in turn causes less density. Therefore, when the air is heated, the volume increases but the density decreases. We can understand it by the equation, $\rho = \dfrac{m}{V}$.
When the air in the sealed container is heated, the volume of the air cannot be increased, so only there is an increase in the pressure.
A better example of this is the hot air balloon. Heating air in a balloon increases both pressure and volume, while the balloon is elastic and does expand but it also provides some resistance to the expansion also.
The fundamental equation for how the gas or the mixture of gases reacts when it's heated is $PV = nRT$. Where, $P$=pressure, $V$=volume, $n$=number of moles of gas molecules, $R$= gas constant, and $T$= temperature.
From this gas equation, we can understand that the heating of air depends on pressure, volume, number of moles of gas molecules, temperature.

$\therefore $ When air is heated it expands.

Note:
The air expands while heating because of the vibration of the molecules in the gas. That vibration causes the air to have more space by bumping into each other. As a result of this expansion, pressure increases, volume increases, but the density of the air decreases.