A mixture of two gases P and Q occupying volumes 300cm3 and 100cm3 respectively exerts a total pressure of 800mmHg. What is the partial pressure of Q?​

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?