When a closed tin is heated, the pressure inside it increases. This happens because:
The molecules move faster and each molecule strikes the walls of the tin more often.
That sounds good to me but you might want to add "more often with more force."
To understand why the pressure inside a closed tin increases when heated, let's consider the behavior of molecules. When a substance is heated, its molecules gain energy, causing them to move faster and collide more frequently with each other and the walls of the tin.
The pressure exerted by a gas (such as the air inside the tin) is essentially the result of these molecular collisions. As the molecules move faster, they strike the walls of the tin more often and with greater force. These increased and more energetic collisions result in a greater amount of force being exerted on the walls, which in turn leads to an increase in the pressure inside the tin.
In summary, the increase in pressure inside a closed tin when heated is due to the increased speed and frequency of molecular collisions with the walls of the tin caused by the higher temperature.