What is the pressure change if you have a constant volume of gas at a pressure of 101 kpa at 25 degrees celsius and increase its temperature to 35 degrees celsius?

Alidded glass container is filled with a colored gas. after a period of time, it is observed that the gas is uniformly spread throughout the box and that the movement has slowed considerably. next, a warm iron plate is carefully placed under the box. why is there resumed movement of the gas in the container?